DESIGN OF NOVEL ENERGY SOURCE FOR FOSTER-MILLER ROBOTS
ME 701-702
Technical Design Report
Design of Novel Energy Source for Foster-Miller Robots Project #3/S01
Final Report
Design Advisor: Prof. Constantinos Mavroidis PhD
Design Team Laura Caputo, Mike Mastovich, Sean O’Blenis, Mike Ringer, Christopher Walker
December 4, 2007
Department of Mechanical, Industrial and Manufacturing Engineering College of Engineering, Northeastern University Boston, MA 02115
1 Table of Contents
CHAPTER 1 INTRODUCTION...... 1 1.1 FOSTER-MILLER...... 1 1.2 PROJECT STATEMENT AND SIGNIFICANCE ...... 3 CHAPTER 2 BACKGROUND...... 4 2.1 CURRENT POWER SOURCES...... 4 2.1.1 Lead Acid Batteries ...... 4 2.1.2 Lithium Ion...... 5 2.2 ALTERNATIVE POWER SOURCE RESEARCH ...... 6 2.2.1 Nickel Cadmium Batteries...... 6 2.2.2 Solar Power ...... 7 2.2.3 Compressed Air...... 8 2.2.4 Wind Power...... 9 2.2.5 Internal Combustion Engine...... 10 2.2.6 Fuel Cells...... 11 2.2.7 Piezoelectrics...... 14 2.2.8 Thermoelectrics ...... 16 2.2.9 Thermophotovoltaics...... 17 2.2.10 Nuclear Power ...... 19 2.3 PATENT RESEARCH...... 20 2.3.1 US Patent #6266576: Legged moving robot...... 20 2.3.2 US Patent #6687571: Cooperating Mobile Robots...... 20 2.3.3 US Patent #7014949: Battery pack and rechargeable vacuum cleaner...... 20 2.3.4 US Patent #4621562: Remote control robot vehicle...... 20 2.3.5 US Patent #6459955: Home cleaning robot...... 21 2.3.6 US Patent #4355508: Air power motor...... 21 2.3.7 US Patent #6838203: Monolithic fuel cell and method for manufacture of same...... 21 2.3.8 US Patent #5049775: Integrated micromechanical piezoelectric motor...... 21 2.3.9 US Patent #5554914: Micro robot...... 21 2.3.10 US Patent #4440118: Oil cooled internal combustion engine...... 22 2.4 COMPETITOR ROBOTS...... 22 2.4.1 PackBot and Warrior X700 ...... 22 2.5 Summary of Current Technology ...... 23 CHAPTER 3 CONCEPT DEVELOPMENT ...... 26 3.1 DESIGN REQUIREMENTS...... 26 3.2 DESIGN SPECIFICATIONS...... 29 3.3 INTERVIEWS...... 30 3.3.2 Shawn Thayer...... 32 3.3.3 Hameed Metghalchi...... 32 3.3.4 Jon Hastie, Jennifer Sarkis, and Tony Aponick...... 33 3.3.5 Mark Jost ...... 34 3.3.6 Rich Kurst...... 34 3.3.7 Kurt Annen ...... 34 3.3.8 Interview Summary ...... 34 3.4 INITIAL CONCEPTS...... 36 3.4.1 Concept 1: Nickel Cadmium Battery...... 36 3.4.2 Concept 2: Lithium Ion Phosphate Battery...... 37 3.4.3 Concept 3: Solar Panels...... 38 3.4.4 Concept 4: Rotary Compressed Air Engine...... 39 3.4.5 Concept 5: Internal Combustion Engine...... 40 3.4.6 Concept 6: Fuel Cell...... 41 3.5 CONCEPT SELECTION ...... 42 3.5.1 Decision Matrices...... 43
2 3.5.2 Additional Concept Elimination Data...... 44 3.5.2.1 Solar Panel...... 45 3.5.2.2 Compressed Air Engine...... 45 3.5.2.3 Nickel Cadmium Batteries...... 46 3.5.2.4 Fuel Cells...... 46 CHAPTER 4 DESIGN AND ANALYSIS...... 47 4.1 DESIGN OVERVIEW ...... 47 4.2 ENGINE SYSTEM ...... 47 4.2.1 Internal Combustion Engine...... 47 4.2.2 Ignition System...... 48 4.2.3 Carburetor...... 49 4.2.4 Carburetor Adapter Block...... 49 4.2.5 Muffler...... 50 4.2.6 Air Silencer...... 52 4.3 Starter/Generator ...... 52 4.4 Cooling System ...... 53 4.4.1 Oil and Pump...... 54 4.4.2 Oil Jacket...... 55 4.4.3 Heat Exchanger...... 55 4.4.4 Cooling Fan ...... 56 4.5 Fuel Tank...... 57 4.6 Batteries...... 58 4.7 Mounting Means...... 59 4.7.1 Structural Analysis ...... 60 4.8 Housing ...... 62 4.9 BILL OF MATERIALS ...... 63 CHAPTER 5 TESTING ...... 66 CHAPTER 6 CONCLUSIONS & FUTURE WORK ...... 70 6.1 Conclusions ...... 70 6.2 Future Work ...... 70 WORKS CITED...... 72 APPENDIX A ...... 74 APPENDIX B...... 87 DEFINITION OF TERMS ...... 87
3 List of Figures
Figure 1: OCU and TALON Robot with major components labeled [1]...... 2 Figure 2: SWORDS Robot [1]...... 2 Figure 3: Lead Acid Battery [3] ...... 4 Figure 4: Lithium Ion Battery [4]...... 5 Figure 5: Energy Density for Different Battery Types [2] ...... 6 Figure 6: Close-up of a Solar Cell [5] ...... 7 Figure 7: Portable Solar Electric Panel from Uni-Solar [6]...... 8 Figure 8: MDI CityCAT Vehicle [7]...... 9 Figure 9: Compressed Air Rotary Engine [8]...... 9 Figure 10: Wind Turbine [9] ...... 10 Figure 11: Saito FA300 Flat Twin Internal Combustion Engine [10] ...... 10 Figure 12: Stages of Operation of a PEM Fuel Cell [12] ...... 12 Figure 13: SERC's Neighborhood Electric Vehicle using PEM Fuel Cells [14] ...... 14 Figure 14: The Piezoelectric Effect [15] ...... 14 Figure 15: Thermoelectric Process [17] ...... 16 Figure 16: A Typical Thermoelectric Device [18] ...... 17 Figure 17: Thermophotovoltaic Cell Diagram [19]...... 18 Figure 18: Midnight Sun Generator Developed by WWU [20] ...... 18 Figure 19: Thermophotovoltaic Device Developed by MIT [19]...... 19 Figure 20: Diagram of Nuclear Fission Process [21] ...... 19 Figure 21: PackBot Developed by iRobot [32] ...... 22 Figure 22: Warrior X700 Developed by iRobot [33] ...... 23 Figure 23 - Volumetric Space Available on TALON...... 29 Figure 24 - Nickel Cadmium Battery Concept ...... 37 Figure 25 - Lithium Ion Phosphate Concept...... 38 Figure 26 - Solar Power Concept ...... 39 Figure 27 - Compressed Air Engine Concept...... 40 Figure 28 - Combustion Engine Concept ...... 41 Figure 29 - Fuel Cell Concept ...... 42 Figure 30 - Saito 60T Twin Cylinder Engine [38]...... 48 Figure 31 - CH Electronics Ignition System...... 49 Figure 32 - Walbro Gasoline Carburetor...... 49 Figure 33 - Muffler Size Chart ...... 50 Figure 34: Inner Tubing of Muffler...... 51 Figure 35: Inner Tubing with Aluminum Piping...... 51 Figure 36: Muffler with Outer Casing...... 51 Figure 37: Final Assembly of Muffler...... 52 Figure 38: McMaster-Carr Air Intake Silencer...... 52 Figure 39: Cobalt 60 Direct Drive Motor [41] ...... 53 Figure 40: Greylor PQ-12 Oil Pump [42]...... 54 Figure 41: Oil Jacket Assembly...... 55 Figure 42 - Heat Exchanger Selection...... 56 Figure 43: Cooling Fan...... 57 Figure 44: Sullivan Products 16oz Fuel Tank [43]...... 58 Figure 45: 12V Lead Acid Battery Pack [44]...... 59 Figure 46: Engine and Starter/Generator Mounting Plate ...... 59 Figure 47: Engine Mounting Brackets...... 60 Figure 50: System Housing ...... 62 Figure 51: Air Flow Diagram ...... 63 Figure 52 - Final Design Layout...... 65 Figure 53 - IC Engine Test Set-up...... 67 Figure 54 - Power vs Resistance Graph...... 68
4 CHAPTER 1 INTRODUCTION
1.1 FOSTER-MILLER
Foster-Miller is currently one of the leading producers of Unmanned Ground Vehicles (UGV’s) for the United States military. The TALON and SWORDS robots are Foster-Miller’s two major units, utilized in various military missions overseas. Currently these robots rely on lithium ion and lead acid batteries for power. The intent of this project is to investigate alternative power sources and implement the new power source into the current systems.
The TALON robot, shown in Figure 1, is generally a reconnaissance vehicle, while the SWORDS robot, shown in Figure 2, is fitted with various weaponries such as M16 rifles, grenade launcher, or anti-tank rocket system. The TALON and SWORDS robots are durable, lightweight, unmanned vehicles that can be controlled from a safe distance using an Operator Control Unit (OCU). The OCU removes the soldier from dangerous situations and has already saved countless lives when disarming bombs, detonating Improvised Explosive Devices (IEDs), removing hazardous materials or exploring dangerous areas. [1]
1
Figure 1: OCU and TALON Robot with major components labeled [1]
Figure 2: SWORDS Robot [1]
2 1.2 PROJECT STATEMENT AND SIGNIFICANCE
One of the major flaws of the TALON and SWORDS robots is their battery life. Currently Foster-Miller’s TALON and SWORDS robots rely on lithium ion and lead acid batteries for power. While these batteries provide sufficient power to the robots, there are unsatisfactorily temperamental and require charge times of up to 8 hours. This project provides a unique opportunity for Foster-Miller to explore alternative power sources. This research paper will discuss the current technologies used by Foster-Miller as well as alternative power sources that could be implemented to improve the run-time and reliability of the current system, and provide proof of concept test results and a complete design of a new power source. The enhancement of these systems will not only improve the performance of the robots, but will ensure the safety and productivity of US soldiers in combat.
3 CHAPTER 2 BACKGROUND
2.1 CURRENT POWER SOURCES
2.1.1 Lead Acid Batteries Lead acid batteries are the oldest form of rechargeable batteries and have remained the most used of all battery technologies for commercial applications. These batteries use a reversible chemical reaction to store energy. A combination of lead plates and dilute sulfuric acid converts electrical energy into potential chemical energy and back again. [2]
The self-discharge of lead acid batteries, shown in Figure 3, is about 40% per year, making lead acids one of the best of rechargeable batteries. Despite this advantage, lead acid batteries take a significantly longer time to charge than most other options and are also susceptible to damage when deep cycling occurs. Deep cycling is the act of fully discharging a battery before recharging, and if a lead acid battery is run until full discharge, its capacity is reduced by a small percentage. Repetitive full discharges will eventually destroy the battery. If the battery is stored at full discharge for a long period of time, it will be irreparably damaged. During typical operation of the TALON robots, two lead acid batteries provide about two hours of battery life with each providing 300 W-hrs at 36 volts of direct current (VDC). [1]
Figure 3: Lead Acid Battery [3]
While lead acid batteries provide enough power to complete the normal tasks they are intended for, improvements can be made. The two hour battery life becomes a constraint when soldiers are performing extended missions, and the long charge time leads to extended periods of inactivity. Additionally, the lead
4 acid battery requires more maintenance in the field than the soldiers should be required to do in their daily tasks.
2.1.2 Lithium Ion Lithium ion batteries consist of three thin metal plates pressed together to form a single unit. These plates represent the positive electrode, negative electrode and separator. The plates are submerged in a solvent and encased in a metal container. When charging, ions move from the positive electrode to the negative electrode, creating a potential voltage.
Lithium ion batteries, shown in Figure 4, are not subject to memory, the effect on a battery where, when not fully discharged after each use before recharging, the unused portion of the battery will crystallize and become unusable over time. Lithium ions are capable of handling high cycling. However, they lose about 5% of their charge every month and will last only two or three years. If completely discharged a lithium ion battery is no longer usable, and is also adversely affected by high temperatures. During typical operation of the TALON robots, one lithium ion battery provide about 4.5 hours of battery life with 750 W-hrs at 36 VDC. [1]
Figure 4: Lithium Ion Battery [4]
5 2.2 ALTERNATIVE POWER SOURCE RESEARCH
This section will investigate a wide range of power source options. It was Foster-Miller’s desire that the group investigate all available options before ruling any out. As such, this section contains power sources, such as wind and nuclear power, that could almost immediately be eliminated; however they were given the proper research to confirm that they were infeasible.
2.2.1 Nickel Cadmium Batteries Nickel cadmium (NiCd) batteries work like lead acid batteries in that they convert a chemical reaction to electricity. Figure 5 below shows where NiCd batteries stand in comparison to those of lead acid and lithium ion as far as their energy densities are concerned. Nickel cadmium batteries have more than 50% greater energy density than lead acid batteries. Although the cobalt lithium ion appears to be the greatly superior option, it is highly explosive, making its immense energy density irrelevant.
Figure 5: Energy Density for Different Battery Types [2]
There are several other advantages to using NiCd batteries. They charge much faster than lead acid or lithium ion batteries and are very durable in harsh working conditions. Unlike lithium ion batteries, NiCd batteries can be fully discharged. They also have a long shelf life and a high number of cycles if properly maintained.
Some of the disadvantages of NiCd batteries are that they can form memory if they are not fully discharged about every month. NiCd batteries also have a high discharge rate, which means that if they sit idle too long
6 they will require charging. Two companies that manufacture high power density NiCd batteries are Cadex Electronics Inc. of Vancouver, BC, and Electro Energy, Inc. of NJ. [2]
2.2.2 Solar Power Solar panels work by absorbing the sun’s light and converting it to power, known as the photovoltaic effect. The solar panels are normally made of silicon. The electrons flow through the silicon after they are knocked loose from their atoms to create power. [5] Figure 6 illustrates the typical components and current flow of a photovolataic solar cell.
Figure 6: Close-up of a Solar Cell [5]
General Electric manufactures solar panels used by Uni-Solar, Inc which can be seen in Figure 7. The 15- watt panels they manufacture can produce 1amp-hour with a weight ratio of 8 – 11.3 watts per kilogram. [6]
7
Figure 7: Portable Solar Electric Panel from Uni-Solar [6]
A major advantage of a solar power system is that it provides electrical power from a free and fully renewable resource. Additionally, because many solar power systems utilize a series of photovoltaic cells, if one cell is damaged or malfunctions the system will not be significantly affected. Current solar panel systems, however, require a large area to produce a relatively small amount of power. Another disadvantage is that a solar power can only be utilized during daylight hours.
2.2.3 Compressed Air When air is compressed, it can be released in controlled amounts in to obtain energy. An engine using compressed air can be as efficient an engine using gasoline or other types of combustible fuel. If compressed air from storage tanks is fed through air injectors into the cylinder, air expands and pushes down the piston. This movement, coupled with other interactions within the engine and associated gear boxes, can be used to rotate a drive shaft.
There are some major advantages to an air powered engine. Engines using compressed air produce zero emissions and are environmentally-friendly. Another advantage is that air is the most readily available “fuel” to use. The self-discharge rate of a tank holding compressed air is much less compared to the self- discharge of all different types of batteries. Also, refilling of the tanks takes a very small amount of time compared to recharging batteries. Compressed air tanks also have a very long storage life, unlike many batteries.
A disadvantage of compressed air is that there is a need for an air compressor to fill the tanks up with air. Also, the storage tanks could be large to achieve long runtimes.
Recently, compressed air engine technology has grown due to increasing worldwide awareness of pollution. The most promising technology uses compressed air to power cars and is being developed by the company MDI. They are currently producing air powered cars for India to be used as taxis. In addition to
8 MDI’s CityCAT shown in Figure 8, other companies, such as K’airmobiles are also successfully producing air powered vehicles.
Figure 8: MDI CityCAT Vehicle [7]
Not all air powered engines must contain pistons. Angelo Di Pietro, an Australian engineer, created a small rotary engine that uses compressed air technology. [8] This engine is shown below in Figure 8.
Figure 9: Compressed Air Rotary Engine [8]
2.2.4 Wind Power A windmill works by taking the kinetic energy of the wind and turning it into electric energy. The wind spins blades which are connected to a generator. When the generator spins, electric power is produced. Wind power is useful because it is clean and renewable. Figure 10 shows a typical windmill.
9
Figure 10: Wind Turbine [9]
Wind power has several disadvantages. In order to produce large amounts of energy, the blades would have to be very large, as would the generator.
2.2.5 Internal Combustion Engine The internal combustion (IC) engine is a technology that has been exploited for just over a century. In an IC engine, fuel enters a small chamber where it is ignited to produce a tremendous amount of energy in the form of an expanding gas. Since its inception, there have been many breakthroughs in combustion engine technology. They can now be made very small to be used in applications where weight could be an issue. Figure 11 shows a small hobby aircraft IC engine.
Figure 11: Saito FA300 Flat Twin Internal Combustion Engine [10]
10
Another advantage of IC engines is that they are cheaper than the more advanced technologies such as fuel cells. Additionally, unlike batteries they do not require charging but rather refueling. Major disadvantages of IC engines are that they are much noisier than the batteries currently used and they produce large amounts of heat.
Small engine technology dates back over a century and is employed today in applications such as unmanned aerial vehicles (UAV’s), small motorcycles, scooters, chainsaws, etc. Manufacturers of these small IC engines include RCV Engines and Saito Engines.
2.2.6 Fuel Cells Fuel cells operate by taking hydrogen fuel and channeling it through the anode side of the fuel cell while oxygen comes in through the cathode side of the cell. A catalyst at the anode then causes the hydrogen to split into both positively charged hydrogen ions and negatively charged electrons. The positive hydrogen ions, also called protons, are allowed to pass through the membrane, which restricts the electrons from passing through. These electrons are forced to travel around the outside of the cell creating an electric current since they cannot pass through the membrane. The oxygen on the cathode side of the cell then joins with the protons which were allowed to pass through the membrane. They form water and flow out of the cell as the only byproduct. [11] Figure 12 shows this process for a Proton Exchange Membrane (PEM) fuel cell..
11
Figure 12: Stages of Operation of a PEM Fuel Cell [12]
Currently, several different types of fuel cells exist. These include a Proton Exchange Membrane Fuel Cell (PEMFC), Direct Methanol Fuel Cell (DMFC), Alkaline Fuel Cell (AFC), Phosphoric Acid Fuel Cells (PAFC), Molten Carbonate Fuel Cells (MCFC), and Solid Oxide Fuel Cells (SOFC). For this project, the most applicable type of fuel cell would be a PEM Fuel Cell due to the fact that their primary applications are automotive and stationary power and they have an operating temperature of 50-100 degrees Celsius [11]. The PEM Fuel Cell is also capable of power outputs of between 50 W and 75 kW [13]. Table 1 illustrates characteristics for all of the types of fuel cells listed above to allow for easy comparison.
12 Table 1: Characteristics of Important Fuel Cells [11] Proton Exchange Direct Molten Membrane Methanol Phosphoric Carbonate Solid Oxide Fuel Cell Fuel Cells Alkaline Fuel Acid Fuel Fuel Cells Fuel Cells (PEMFC) (DMFC) Cells (AFC) Cells (PAFC) (MCFC) (SOFC) Automotive Space vehicles Vehicle Primary and Portable Stationary Stationary and drinking Auxiliary Applications stationary Power Power Power water Power power Molten Concentrated carbonate Polymer Polymer Concentrated Yttrium- 100% retained in a Electrolyte (plastic) (plastic) (30-50%) stabilized phosphoric ceramic membrane membrane KOH in H2O Zirkondioxide acid matrix of LiAlO2 Operating Temperature 50-100°C 0-60°C 50-200°C 150-220°C 600-700°C 700-1000°C Range Prime Cell Carbon- Carbon- Stainless Carbon-based Graphite-based Ceramic Components based based Steel H2, CO, Primary Fuel H2 Methanol H2 H2 H2, CO CO4 Start-up Time Sec-min Sec-min Hours Hours Hours Power Density 3.8-6.5 Approx 0.6 ~1 0.8-1.9 1.5-2.6 0.1-1.5 (kW/m3) Combined 30-40% (no Cycle Fuel 50-60% combined 50-60% 55% 55-65% 55-65% Cell cycle) Efficiency
PEM fuel cells provide 0.7 volts and can have power densities up to 1 W/cm2. In order for these to work properly and achieve the desired power, the hydrogen gas must have less than 10 ppm of CO in it [11]. Since the PEMFC requires water, it requires air with high humidity so the membrane has moisture and it is able to operate. This could make operation in a desert environment difficult since the temperature can vary greatly between day and night and the humidity is low. Although a fuel cell will work if air comes into the cell from the cathode side, the performance will increase 30% if the cell can obtain pure oxygen on its cathode side instead of just outside air. [11]
One major advantage of a fuel cell is its high energy density. They have endurance in low temperatures and will not discharge, like many batteries, if left sitting on a shelf. Fuel cells do not require charging but must be refueled. Another advantageous aspect of fuel cells is that there are no moving parts and everything is easily contained in one unit. They are also quiet since there are no moving parts.
13 The major disadvantage of fuel cells is that they are very temperamental. Since they are still such an unfamiliar technology, it is not yet known how to make them run perfectly. PEM Fuel Cells are very sensitive to any impurities that may exist in the fuel. They are fragile and may not handle moving around well.
The Schatz Energy Research Center (SERC) currently has two fuel cell vehicles providing an example of a fuel cell being used to power a small vehicle. Their Neighborhood Electric Vehicle is shown in Figure 13.
Figure 13: SERC's Neighborhood Electric Vehicle using PEM Fuel Cells [14]
Both of the SERC’s vehicles operate using PEM fuel cells. Each one contains multiple cells in large stacks as well as hydrogen tanks at a certain gas storage pressure. The SERC’s contain 96 cells and operate with a power output of 9kW at 600mV/cell. The vehicles get about 70mpg with a range of about 30 miles, and have the capability to achieve 35 mph. They also have a fast refueling time of two minutes, a decided advantage over all battery technologies. [14] In addition, Ballard and NUVERA are two other companies that sell fuel cells.
2.2.7 Piezoelectrics Piezoelectric transducers, shown in Figure 14, use mechanical stress or vibration to generate an electrical charge. The technology is improving to make transducers stronger as they are now being made from advanced man-made ceramics rather than natural quartz crystals.
Figure 14: The Piezoelectric Effect [15]
14
Piezoelectric transducers have the potential for a very high output in a very small amount of space. The major problems with these transducers are that they are very fragile. In addition, a vibration or mechanical stress needs to be created for them to work properly. Table 2 shows the specifications for the piezoelectric transducers made by Piezo Systems Inc of Cambridge, MA.
Table 2: Piezoelectric Properties [16] Piezo Systems' Designation PSI-5A4E PSI-5H4E Navy type II; Navy type VI; Industry Designations Industry Type 5A Industry Type 5H Lead Zirconate Lead Zirconate Composition Titanate Titanate
(@ 1 Relative Dielectric T K 1800 3800 Constant KHz) 3 Piezoelectric "d" coefficients relate the Strain Produced / Electric Field Applied or the Short Circuit Charge Density Produced / Stress Applied meter/Volt or d 390 x 10-12 650 x 10-12 33 Coulomb/Newton meter/Volt or d -190 x 10-12 -320 x 10-12 31 Coulomb/Newton Piezoelectric "g" coefficients relate the Open Circuit Electric Field Produced / Stress Applied or the Strain Produced / Charge Density Applied Volt- -3 -3 g33 meter/Newton or 24.0 x 10 19.0 x 10 meter2/Coulomb Volt- -3 -3 g31 meter/Newton or -11.6 x 10 -9.5 x 10 meter2/Coulomb
Coupling Coefficient k33 0.72 0.75
k31 0.35 0.44 Polarizing Field Ep Volt/meter > 2 x 106 > 1.5 x 106 Initial Depolarizing Field Ec Volt/meter ~ 5 x 105 ~ 3 x 105 Coercive Field Ec Volt/meter ~ 1.2 x 106 ~ 8 x 105 MECHANICAL Density δ Kg/meter 7800 7800 Mechanical Q 80 32 E 2 10 10 Elastic Modulus Y 3 Newton/meter 5.2 x 10 5.0 x 10 E 2 10 10 Y 1 Newton/meter 6.6 x 10 6.2 x 10 THERMAL Thermal Expansion Coefficient meter/meter °C ~ 4 x 10-6 ~ 3 x 10-6 Curie Temperature °C 350 230
15 2.2.8 Thermoelectrics Thermoelectric devices have been used for many years by engineers and scientists for a variety of applications. They are primarily used for heating and cooling regulation, but are also used for power generation. In its simplest form, thermoelectrics is the use of a temperature difference to generate electrical current. As it pertains to power generation, it is based upon the principle of the Seebeck Effect, discovered in 1821 by Thomas Johann Seebeck. The Seebeck Effect occurs when two wires of a thermoelectric are connected in series. In the presence of a temperature difference between the junctions, current flows around the circuit.
The thermoelectric effect occurs by first applying direct heat flow, creating a higher temperature on one side of the thermoelectric module. This creates a temperature difference between each side of the module. The charged carriers in the material then diffuse from the hot side to the cold side, leaving behind their oppositely charged nuclei on the hot side. This separation of charges creates an electric field, as shown in Figure 15.
Figure 15: Thermoelectric Process [17]
In order to create a great enough temperature difference, most systems on the market employ a heating system on one end and a cooling system on the other, creating the greatest temperature difference possible. To generate large amounts of power, these systems become larger and larger, dragging down the power density. Most are run through underground gas pipelines rendering them immobile.
In theory, with the Seebeck Effect an infinite amount of energy could be created between two points by simply creating the largest temperature gradient possible. However, this does not hold true due to the Second Law of Thermodynamics and the realities of the system. A major factor that decreases the power output of these systems is significant heat loss and resistance that occur within the layers of the system. This makes for a very inefficient system.
16 Thermoelectric power is currently being studied and improved extensively, and may someday be a very efficient method of power generation, once the inefficiency obstacles can be overcome. Figure 16 shows a typical thermoelectric device.
Figure 16: A Typical Thermoelectric Device [18]
The majority of companies creating thermoelectric devices with the capabilities to generate power are doing so on a very small scale. Many devices are millimeters in square area, and are intended to power or recharge small devices such as watches, small LCD displays and other various low power applications. Vendors who currently sell thermoelectric devices include are D.T.S, Global Thermoelectrics and Kyrotherm.
2.2.9 Thermophotovoltaics Thermophotovoltaics (TPV) is the generation of power by converting light emitted by a heated material into energy. Thermophotovoltaics has been around since the 1960s, but has never been commercially developed.
In this system a material is heated, usually using a fuel such as gasoline, to extreme temperatures. This causes the material to radiate photons. The photons travel through a filter which allows photons with the proper amount of energy through, and bounces back those that do not. This step increases the efficiency of the system by recycling photons that would not create any energy in the system. The photons then enter a photovoltaic cell (PV) which converts them to energy and burns off any waste heat. Figure 17 shows the method of electrical production from a thermophotovoltaic cell.
17
Figure 17: Thermophotovoltaic Cell Diagram [19]
The key to photovoltaic systems is creating the greatest efficiency by matching the wavelength of the photons being released from the emitter to the selective filter in the second step of a TPV system. Many of the recent advancements have come from the discovery of new matching materials.
In 1995, Western Washington University released the “Midnight Sun Generator”, shown in Figure 18, which was a TPV system that could reportedly produce 900W of power [20]. No further information could be found, and no size specifications were given.
Figure 18: Midnight Sun Generator Developed by WWU [20]
In 2006, MIT announced initial information on a TPV system that could replace the alternator used in cars. This device is shown in Figure 19. No follow up information has been found, nor any details on the efficiency or power capabilities of the device. [19]
18
Figure 19: Thermophotovoltaic Device Developed by MIT [19]
2.2.10 Nuclear Power Nuclear power works using the fission of uranium atoms to excite electrons which release energy. This process triggers chain reactions to generate massive amounts of energy. Figure 20 shows the nuclear fission process.
Figure 20: Diagram of Nuclear Fission Process [21]
A major advantage of nuclear power is that a large amount of energy can be obtained and easily scaled down. There are several disadvantages to nuclear power. Nuclear power is intended for large scale power generation. The main disadvantage is that there are very strict handling procedures as it is a very volatile source of energy.
19
2.3 PATENT RESEARCH
By analyzing current patents relating to power sources and robotics, more can be learned about what is being used in today’s technology. Additional uses for the current research that are not covered in the intellectual property arena may also be discovered. These patents were found by searching for fuel cells, lithium-ion, lead-acid, solar, compressed air, piezoelectric, and thermoelectric power sources and their applicability to robotics.
2.3.1 US Patent #6266576: Legged moving robot. This patent describes a legged moving robot powered by a fuel cell. It is stated that the attraction of fuel cell power is its greater energy storage capacity per weight than lithium-ion batteries, absence of vibration from the fuel cell’s output, and absence of harmful emissions. The robot may contain a storage means for raw material from which to generate power from the fuel cell [22]. The technology described in this patent may be a good fit for the TALON’s electric power needs.
2.3.2 US Patent #6687571: Cooperating Mobile Robots. This patent describes a miniature mobile robot, equipped with sensors and designed to work in teams to search an area. This robot is powered by lithium-ion batteries by Tadrian Batteries Ltd., specifically INCHARGE rechargeable batteries of size 2/3 [23]. This lithium ion technology is similar the that currently used in Foster Miller’s robots, to a much smaller scale.
2.3.3 US Patent #7014949: Battery pack and rechargeable vacuum cleaner. This patent describes a lithium-ion battery pack for a rechargeable vacuum cleaner. The battery pack consists of rows of cylindrical lithium-ion batteries encased with outer walls designed to channel air over the batteries for cooling [24]. The battery pack described in this patent is similar to the pack currently used in the Foster-Miller robots, where a number of cylindrical lithium ion batteries are connected in a combination of series and parallel to achieve the desired electrical output.
2.3.4 US Patent #4621562: Remote control robot vehicle. This patent describes a remote control robot vehicle with onboard closed circuit television cameras, a rotateable robotic arm with gripping means, and a mountable shotgun on the robot arm. This robot is powered by a heavy duty 12-volt lead-acid battery [25]. The applications of this robot are very similar to those of the TALON robot, and the lead acid power supply is similar to the one used by the current Foster- Miler robots.
20 2.3.5 US Patent #6459955: Home cleaning robot. This patent describes a robot capable of being adapted for multiple uses. One application described is a weed-killing robot capable of identifying and destroying a weed with an infrared ray. This robot is capable of being powered through a solar recharging power cell through an amorphous silicon solar cell or film [26]. This solar technology may be adapted as a primary or supplemental power source for the TALON robot.
2.3.6 US Patent #4355508: Air power motor. This patent describes a motor that utilizes compressed air to drive a drive shaft. The compressed air is circulated from a high pressure tank through a member which reacts with the air, then a pressure regulating member followed by an intermediate tank, then back through the air reactance member, which drives a drive shaft for mechanical power [27]. The compressed air motor described in this patent, in combination with an alternator for converting the mechanical power output to electrical power, may be a suitable option for the TALON.
2.3.7 US Patent #6838203: Monolithic fuel cell and method for manufacture of same. This patent describes a monolithic fuel cell made of triplex layers of anode-electrolyte-cathode and a substrate that provides interconnects between the layers. Additionally, a manufacturing method is defined which is low cost and high speed, using computer-aided tools to define the cell’s specifications and robotic stations for fabrication [28]. This fuel cell, with its ease of manufacturing, may be a good choice for the TALON robot, which requires production of a high volume of power supplies to meet the robot’s ever increasing demand.
2.3.8 US Patent #5049775: Integrated micromechanical piezoelectric motor. This patent describes small machines comprised of cantilever beams covered with piezoelectric material which drive the beams to perform mechanical tasks. Also defined is the process in which this technology may drive a robot to move, grab, or carry objects [29]. This technology may be a viable option to provide supplemental power for the TALON’s many electrical power needs.
2.3.9 US Patent #5554914: Micro robot. This patent describes a robot equipped with sensors for detection capability, driving units to provide movement, controls to regulate movement and detection, and a rechargeable power source. It is suggested that the robot may be equipped with a photovoltaic or thermoelectric generation element to provide electricity and automatically charge the power source [30]. The photovoltaic and thermoelectric elements described in this patent could provide Foster-Miller’s robots with the increased battery life they desire. By recharging the battery while the robot is in use, this application may lead to extended mission durations, a major goal of this project.
21
2.3.10 US Patent #4440118: Oil cooled internal combustion engine. This patent describes a system of cooling an internal combustion engine using lubricating oil. The major concept for this design is a cylinder liner that allows a very thin layer of oil, less than .016 inches of flow diameter, to pass axially across the exterior cylinder wall. This thin layer produces a laminar flow that produces a large convective heat transfer coefficient [31]. Though similar to the oil cooling system described later in this report, this system describes an axial cooling system while the system designed here utilizes radial oil flow.
2.4 COMPETITOR ROBOTS
2.4.1 PackBot and Warrior X700 One of the largest competitors for Foster-Miller’s TALON and SWORDS robots is iRobot’s PackBot, shown in Figure 21. PackBot weighs only 53 lbs when fully loaded and runs off of two nickel cadmium battery packs. These two NiCad battery packs provide PackBot with anywhere from two to twelve hours of runtime. They also allow PackBot to travel for at least six miles. [32]
Figure 21: PackBot Developed by iRobot [32] iRobot has another modular robot called the Warrior X700, which is shown in Figure 22. This robot is very similar to TALON in the fact that they both rely on the use of Lithium Ion batteries.
22
Figure 22: Warrior X700 Developed by iRobot [33]
2.5 Summary of Current Technology
Through initial research it becomes apparent that several power systems are not feasible options for the TALON robot.
Nuclear systems provide tremendous amounts of power, but are not an option because they have not been utilized on a small scale level. There is also an element of user acceptance that would have to be addressed.
Wind power is a very safe a clean method of power generation, but requires a large scale system in order to generate significant amounts of energy. Inconsistency of favorable conditions would become an issue.
Piezoelectric devices are intended for small scale uses, and would not be able to accommodate the desired power requirements. Currently they are only used in low power applications.
Thermophotovoltaic power is currently being studied and improved extensively, and may someday be a very efficient method of power generation, once the technology is perfected. The technology could be used as a standalone, fuel-driven system that would be easy to use and would not be driven by a battery. No charging would be involved, and would eliminate many of the problems of the TALON.
Thermopohotovoltaics is a technology that is being studied, but is unproven. There are no current products available on the market. Several universities and companies are developing TPV power systems, but the availability of these products is unreliable and would most likely come at a high cost. The power density of the proposed TPV systems is not expected to be enough for the TALON application.
23
Because solar power cannot solely generate enough power to run the TALON robot, it might be applicable as a supplemental power source adjacent to a main power source. The advantages of solar power are that the robot could run partially off of the solar panels therefore helping the batteries to last longer. Also, the solar panels of the GE product each operate individually from each other. This would be an advantage in combat situations, which would allow the panels to continue power the system even in the event of damage from enemy fire.
A major disadvantage to solar power is that the robots would have to be used during the day. The majority of missions are run at night, eliminating the advantages of solar power. There would also be more components needed to make sure there is no over charging and to prevent discharging in low-light conditions.
The TALON robots are generally used in desert conditions, located near the equator. The adverse conditions of the typical usage of the Talon robots could increase the temperature difference required to generate enough power. Also, there are several applications in which thermoelectric devices were used as heat recovery systems. These systems use excess heat that is burned off from a power source to increase the temperature difference across the system. Thermoelectric devices could be used as a complimentary system to improve the efficiency of a main power system.
In order to generate the power that is needed to run the TALON robots, very large systems are needed. These systems tend to be stationary, and are anchored to some source of heat generation. Thermoelectric power generators that would fit onto the robot would not supply a significant amount of power to run because of the very low power density.
Fuel cell technology may be an option, but this could only be verified by further research and testing. Due to an initial hesitance to replace the current batteries with fuel cells, and the high cost that would be associated with testing such technology, fuel cells will be a secondary option. At the request of Foster- Miller, more research will be conducted in the field of fuel cell technology.
Nickel cadmium batteries appear to be a viable option as a power source. These batteries provide a higher power density and are not affected by cycling without full discharge. Also, the nature of these batteries appears to be more conducive to the actual field uses.
24 Current compressed air rotary engines appear to be a viable option as a power source, and would be readily available from Engineair. The company has already tested the product in similar applications.
Internal combustion engines are a common technology that has already been proven. With recent advancements, the size of engines has reduced significantly enough to fit within the small constraints of the TALON robot. Combustion engines could employ JP8 as its main fuel, which was Foster-Miller’s initial goal.
25 CHAPTER 3 CONCEPT DEVELOPMENT
After completion of the background research, concept generation began for a new power source. Ideas were generated as a team using information from Foster-Miller, patent research, background results and interviews with professors with extensive research experience in the industry. Each concept was cross referenced with the design specifications for feasibility and then a decision was made using several design and development tools.
3.1 DESIGN REQUIREMENTS The design of the new power source for TALON and SWORDS robots has several well defined criteria that will be used to select feasible power sources to test. All specifications were developed with the help of Foster-Miller and were based on the performance of the current batteries used in the robot. An extensive list of topics discussed with Foster-Miller can be found in the interview Section 3.3. A list of the major design criteria can be found in Table 3.
In an attempt to improve the system the capacity and battery life of the new system will have to exceed the capabilities of the current system. Therefore, the power source should have a greater capacity and battery life and the system should have a volume , weight and charge time that are equal or lesser than the current system. The system will need to operate between 36 – 42 volts, and will have to be powered by means of electrical power only. The system must be rugged and easily connected into the system and should not be affected by temperature. This system must deliver up to 300 watts of power to the robot in order to function. Foster-Miller would prefer that the system not be extremely loud and that if at all possible, it could run off of readily available fuels.
26 Table 3 – Design Criteria Significance Category Units Weight Capacity Wh/kg 5 Battery Life hrs 5 Voltage Supplied V 5 Size in 3 Charge Time hrs 3 Robustness - 3 Water Tight/Dust Proof - 2.5 Weight lbs 3 Temperature Dependence ºC 2 Form of Power - 5 Max Power Output W 4 Foster-Miller Input - 5 Capstone Time Constraint - 3.5
• Capacity – The most important design criteria is the measure of the capability of a power source to deliver power for a significant amount of time. Capacity increases with size and also varies between battery chemistries. A logical balance of these two qualities is critical to maximizing this specification.
• Battery Life – Directly related to capacity is the length of time for which a power source will provide usable power. The battery life of the new power source must be significantly more than the current power sources. This specification will be verified through extensive testing of viable power sources.
• Voltage Supplied – The TALON robot’s electrical systems currently operate at 36 volts. The voltage of any new power system should match that of the current systems.
• Size – There is a very limited amount of space available on the TALON for a power source. Currently the batteries used are custom designed to fit in a small bed, while allowing for the TALON arm to move in and out of the path down the center of the robot. The TALON currently also uses a side rack, which can be quickly attached or detached for additional space.
• Charge Time – Currently the TALON comes with two batteries. One is charged while the other is in use. The charge time of the current power sources is larger than the run time. Ideally, this charge time will be decreased in order to eliminate the layover of charging time.
27 • Robustness – The TALON robot is used in harsh conditions in which it will see significant vibrations. The new power source must not be susceptible to such conditions. This will not be tested, only verified through product information.
• Water Tight/Dust Proof – The TALON robot will be exposed to normal environmental conditions as well as severe desert conditions. Therefore, the power source must be completely sealed. This will not be tested, only verified through product information.
• Weight – The current power systems have a specific weight that must be met so as not to decrease the performance of the robot. An increase in weight increases the overall payload of the robot, decreasing performance and possibly cancelling any increases in capacity. Also, an increase in weight would eliminate the advantage that the TALON provides by being easily transportable.
• Temperature Dependence – The TALON robot is used in harsh conditions in which it will see a wide range of temperatures. The new power source must not be susceptible to such conditions. This will not be tested, only verified through product information.
• Form of Power – One of the preferences of Foster-Miller is that the new power source not require any significant redesign of the TALON robot. The TALON currently provides electrical power to brushless motors and other electrical systems. Therefore, the new power source should deliver electrical power, not mechanical power to avoid a complete redesign of the TALON drive train systems.
• Maximum Power Output – Through previous Foster-Miller testing it has been determined that there is a nominal amount of power drawn from the electrical and mechanical systems, as well as a maximum surge power drawn at any given time. The new power systems must be capable of handling the power needs of the TALON robot.
In an attempt to simplify the design of a new power source, it is the intent of Foster-Miller that the chosen design will fit in the space currently occupied by the lead acid and lithium ion batteries. This avoids the need to redesign the robot itself in any way. A diagram of the maximum dimensions can be seen below in Figure 23.
28
Figure 23 - Volumetric Space Available on TALON
There is, however, currently an option for a mounting platform located over the treads of the robot. These platforms are readily available at Foster-Miller and are currently in use. Several of the options that are available for the TALON robot require extra packaging for additional equipment such as firing mechanisms, surveillance devices and signal jamming devices. This platform would allow for additional power equipment if the benefits of such a system were worthwhile.
3.2 DESIGN SPECIFICATIONS Based upon the criteria defined by Foster-Miller, the team came up with a set of specifications that the new power source must meet. The detailed current and desired design specifications can be seen below in Table 4.
29 Table 4 - Design Specifications
The list below gives a description of how some of the less obvious categories pertain to this application. • Inactive Battery Life – When a battery is inactive, for a long period of time there is a tendency for the battery to naturally lose its charge. The current inactive battery life of lead acid batteries is around 8 months. Maximizing shelf life is a specification which should be met as closely as possible. • Ease of Connection – Current the batteries used in the TALON robot plug directly into the electrical system. The makes for easy movement of the battery in and out of the robot when needed. The new system should contain a simple connection system as well. • Commercially Available – The parts used in the power system must be commercially available and easy to access. This will simplify the design process as well as the purchasing process afterwards. • Safety – The power source should not be susceptible to any potentially dangerous situations. All possible safety concerns should be accounted for in advance. • Fuel Availability – If possible, the use of fuel that is already implemented in the field of use should be used. This will eliminate the need for more supplies on site.
3.3 INTERVIEWS
In order to better understand which power options are feasible as well as what products currently exist on the market, it was necessary to conduct interviews with various experts in the fields of robotics and power. The goal of each interview was to guide the design towards a more feasible power option within the time
30 frame for the project.
3.3.1 Michael Goldfarb, Ph.D Michael Goldfarb, professor at Vanderbilt University, specializes in the field of robotics especially dealing with high energy density robotic actuators. He has been involved with numerous robot design projects.
Dr. Goldfarb was concerned with the actuation of the robotic arm on the TALON. He mentioned that an internal combustion engine would not provide us with the level of actuation required and that we might need to consider pneumatics or hydraulics.
As far as the internal combustion engine is considered, Professor Goldfarb explained that its advantage is that gas provides the highest energy density, but it has many disadvantages. These include noise, reduced efficiency as the engine becomes smaller, and difficulty starting and stopping. He felt that using internal combustion engines still requires a lot of work as these have a long way to go. He stated he was not sure if there were any options in existence that would be better than a battery.
Professor Goldfarb mentioned an example of one robot using a 5 horsepower engine which was very expensive but had a fuel into work output percentage of 2-3% and was funded by DARPA.
He recommended looking into RC engines, engines designed for use in small remote control vehicles, as a possibility. A small engine could be attached to an alternator, use gas and would be able to stay within a ten pound weight limit. He recommended preforming calculations and still having a battery to go along with the engine.
The question of engine interference with the existing camera equipment on the TALON was a concern. Professor Goldfarb stated the motors should not create interference with the camera equipment. However, they will give off vibrations and require some consideration for cooling and may even need to go as far as a thermoelectric cooler.
Professor Goldfarb did not think that fuel cells will work as a feasible power supply for the TALON. They are more commonly used as backup power supplies in applications much larger than that of this project.
He said that nickel cadmium batteries had gotten better, but he was still unsure if they would provide a longer lifetime and greater power density in the long run than the lithium ion. He mentioned nickel metal hydride for their energy density as well. Between the batteries he stated the best were the lithium ion and
31 the lithium polymer rechargeable. He said the lithium polymer batteries found in RC cars may be a better choice than the current batteries.
Professor Goldfarb was extremely helpful throughout the interview at providing alternative leads for contacts as well as additional research for this project. [34]
3.3.2 Shawn Thayer
Shawn Thayer is a current contractor at Foster-Miller, and more importantly, a retired Sergeant of the United States Army in the explosive ordinance disposal (EOD) division and is very knowledgeable of the use of robots in the field.
Shawn stated that the ideal battery for use in the TALON would be less than twenty pounds and able to last for at least four hours while under continuous use. Weight can be a big issue so the lightest battery available is preferred. The ideal batteries also require a quick charge time and would have to be able to be used in all environments including hot and cold, wet and dry, and high and low humidity.
The problem with the current batteries is that the lead acids are good batteries, but they are heavy and have a short life. The advantages also include that they are not difficult to use and are inexpensive. The lithium ions are also good batteries. They are lightweight and have a longer life than lead acid. These batteries do, however, require training the soldiers in proper use to avoid issues that may arise recharging and connection to the robot. They are also expensive.
Shawn stated that in Iraq and Afghanistan, noise was not a concern for bomb technicians. The only area where noise may become a concern would be in the SWAT arena. [35]
3.3.3 Hameed Metghalchi
Hameed Metchalchi, professor in Mechanical Engineering at Northeastern University, has a background in internal combustion engines.
Professor Metchalchi discussed the idea of using an internal combustion engine along with a smaller battery to power the TALON robot, but thought that it would be too difficult in our time frame to integrate an engine and alternator into the system. He also, reaffirmed the fact that substituting a mechanical system for an electrical system would require significant design changes to the drive train system. He worked out some calculations as well as discussed horsepower capabilities and which sizes would be best suited to meet the application of the TALON robot and its requirements. [36]
32 3.3.4 Jon Hastie, Jennifer Sarkis, and Tony Aponick
Jon Hastie, Jennifer Sarkis, and Tony Aponick are all employees of Foster-Miller, currently working as the liaisons for this capstone project. They are continuously being contacted on this project for their opinions and knowledge of the TALON robots.
After discussing initial design concepts with them, they would like to rule out nickel cadmium batteries as an option. They feel they would not provide much more runtime than the lithium ion so the change would not be worth it. Also, the nickel cadmium batteries can be very temperamental and would not solve a lot of the current issues with the lithium ion batteries. They would require discharging before recharging each time or the battery would become useless.
Jon, Jennifer, and Tony are interested in internal combustion engines and feel these could be a promising area. An examination of the Foster-Miller robots showed that there are racks attached to the tops of the robots. An internal combustion engine system could be placed on one of these racks and be used as a long range pack for longer operations. This provides a good marketing edge for the company in addition to being able to provide more power because it allows them to sell the internal combustion rack as an accessory to the robot. In addition, the internal combustion engine system would most likely provide enough power to allow the system to then be adapted to Foster-Miller’s other larger robots as well as the TALON.
Fuel cells also seem to be a promising area. Foster-Miller has some contacts at Protonex Fuel Cells. Protonex has goals of making a fuel cell system that can be applied to military UGV’s such as the TALON. They currently sell a fuel cell battery on its own that could be adapted to the robot through this project. It is believed that Protonex may be able to have a usable fuel cell within 8 weeks according to Sam Tolkoff, another employee of Foster-Miller.
Solar Power does not provide sufficient enough energy to fully power the robot. It was concluded that it would take too many solar panels for it to be even possible to reach the power output required. This would take up more space than desired as well as add too much weight to the robot.
Lithium sulfur batteries were discussed after the interview with Professor Goldfarb. Jon, Jennifer, and Tony were all interested in these batteries and feel they are worth looking into. The lithium sulfur seems to provide a much higher energy density in a smaller space.
The compressed engine idea was also presented to the project contacts at Foster-Miller. Although they were intrigued by this option it does not seem as if it is feasible for this project. It would require too much air to run it for the minimum time required of four hours. This would take up an extreme amount of space on the
33 TALON as well as add a lot of weight. Although carbon fiber tanks could be used, which are lighter, it would still be too much weight to add on.
After these discussions with Foster-Miller the feasible power supply options for this project were narrowed down to fuel cells, an internal combustion engine, and lithium sulfur batteries. Solar panels will not provide enough power, nickel cadmium will not have enough of an advantage where it is worth dealing with its temperamental ways, and compressed air requires too much air to power it on the longer missions.
3.3.5 Mark Jost
Mark Jost is an engineer at SION Power. The team talked to Mark about lead time and possible samples for Lithium Sulfur rechargeable batteries. Mark mentioned that SION is moving facilities and is shutting down from October 16, 2007 through the end of the year. Also, they have obligations to current customers through September 2008. Currently they are the only producers of Lithium Sulfur technology.
3.3.6 Rich Kurst
Rich Kurst is an employee of Aved Electronics. The team spoke with Rich about the packaging of Lithium Sulfur Dioxide SAFT batteries. Rich spoke about how many lithium chemistry batteries are primary or non-rechargeable including Li-SO2. He told us to look into Li-Ion Phosphate rechargeable batteries.
3.3.7 Kurt Annen
Kurt Annen was very helpful in describing how a generator would help drive the robot. He explained that there are two options. Option one would have a generator hooked up to the battery charger, which would constantly charge the battery as the robot took power from the battery. The problem with this is that batteries are subject to damage due to over charging. Option two would have generator power run into an AC to DC converter that would feed directly into the robot. The robot would then run whenever the generator was running. [37]
3.3.8 Interview Summary Table 5 below shows a summary of the significant issues discussed in the above interviews.
34 Table 5 – Interview Summary Chart Interviewee Question Answer Resulting Action or Decision Michael Goldfarb What are the advantages of an internal Internal combustion Looked into RC engines combustion engine? engines provide highest energy density. What are the advantages of a fuel cell? Fuel cells more suitable Looked into more for power backup than this options, but started to rule application out as feasible option We currently are using lithium ion Lithium polymer batteries Considered lithium batteries, do you know of a better tend to be better than polymer as additional battery chemistry we could use? lithium ion or nickel concept cadmium Shawn Thayer How much of a concern is noise when Noise not a concern Able to consider using these robots? combustion engine, realizing that this is not top priority Hameed Metghalchi Could we use an internal combustion to Recommended using a Discusssed option with mechanically drive the robot system with an internal Foster-Miller and used as combustion engine strong design concept powering a battery Jon Hastie, Jennifer Sarkis, Tony Have you previously looked into nickel Nickel cadmium been Did calculation to prove Aponick, Sam Tolkoff cadmium batteries? considered and does not theory and ruled out as provide a large increase in top concept choice runtime Is there room to spare if an internal Internal combustion Further proved this to be combustion engine was exercised as an engine could be attached feasible concept and option? to rack and used as long allowed space constraint range mission pack within robot to be ignored
Protonex is currently working with Protonex is company most Due to time constraints on Foster-Miller on a fuel cell to power likely to be able to project, ruled out as the TALON, should we continue to produce a fuel cell for this feasible option for now, look into fuel cells as an option? application. Could but Foster-Miller may still possibly have something want to consider for within 8 weeks future research as technology becomes more available. Could solar power be a complimentary Solar power does not seem Did calculations to prove power source? efficient enough to run this correct as well as see TALON for desired time how many solar panels would be required
What research has Foster-Miller done Lithium sulfur has never Used as design concept into lithium sulfur batteries? been looked into before and further researched and seems promising lithium sulfur batteries Mark Jost What would be the lead time for a Factory is shutting down Ruled out as option due to lithium sulphur (Li-S) battery? for three months, can not the fact that SION is the get to request until only company September 2008 manufacturing Li-S Rich Kurst What would be the lead time for a Depends on packaging of Batteries are in stock and lithium sulphur dioxide (Li-SO2) batteries and voltage available for testing battery? requirements Is there any reason that these batteries This type of battery is not Ruled out as option due to could not be used for strenuous military rechargeable. the fact that they cannot activity? be recharged Kurt Annen How would we go about hooking up a It could connect directly to There are two options to generator to produce power the robot as a power look at when using a source, or use it to charge generator for power a battery
35 3.4 INITIAL CONCEPTS After considering the design specifications and design criteria, reviewing the background research and speaking with Foster-Miller, several initial concepts were generated by the team. Many of the initial ideas were ruled out due to their inability to fulfill one or more of the design specifications. This left five viable power supply concepts that could possibly improve the on the current system in the TALON robot.
3.4.1 Concept 1: Nickel Cadmium Battery A nickel cadmium battery system, shown in Figure 24, could be swapped into the system to replace the current battery in the robot. It is believed that the advancements of the last few years have greatly improved the nickel cadmium battery to a point that may eliminate some of the previous concerns. This battery would be customized to maximize the available space on the robot, increasing the capacity as much as possible. Due to the nature of nickel cadmium batteries, it is better for the cycling of the battery if the battery is fully discharged every time. This does not coincide with the realistic use in the field. Therefore an additional rapid discharging system would be needed. This rapid discharging system would be used when a battery was taken out of a robot, but had not fully been discharged. Since all missions must begin with a fully charged battery, this system would rapidly discharge the nickel cadmium battery and then immediately begin charging it again. This would increase the charge time, but would also increase the life of the battery.
36
Figure 24 - Nickel Cadmium Battery Concept
The advantages of this system are that the new nickel cadmium batteries could possibly have a larger capacity than previously thought. The disadvantages of this system are that if one cannot be found, the nickel cadmium battery will be too heavy too provide any significant increase in the performance of the system.
3.4.2 Concept 2: Lithium Ion Phosphate Battery The lithium ion phosphate concept is very similar to that of nickel cadmium. The battery could be used in place of the current power systems, and would simply be a change of battery chemistries. The lithium ion phosphate battery has a higher power density than that of the current lithium ion batteries, and is therefore believed to perform better. The batter packs would be placed into a customized housing that would maximize the space used. This would extend the battery life, without taking up any more space than is used now. Figure 25 shows a schematic of this design.
The advantages of this system are that it would not take up any additional space or weight, while delivering the same performance. There would be a high ease of connection and no adverse cycling affects.
37
Figure 25 - Lithium Ion Phosphate Concept
3.4.3 Concept 3: Solar Panels Solar power could be utilized to recharge the system using one of two concepts. The first would be a fold out solar panel mat, which was discovered during background research. This mat would be draped over the area that the arm occupies. The mat would provide power during day missions, and could increase the battery life. The second concept would be a solar panel attached to the end of one of the antennae on the robot. This panel would provide the same type of extra power that would increase the battery life of the system. These concepts can be seen below in Figure 26.
The advantages of this system are that they require no fuel of any kind, due to their renewable energy source. This system would also be very lightweight and mobile. The disadvantages of this concept are that they might not provide enough power to significantly increase the life of the system.
38
Figure 26 - Solar Power Concept
3.4.4 Concept 4: Rotary Compressed Air Engine A rotary compressed air engine would operate in the same manner as the internal combustion engine, but instead of a gas powered engine with a gas tank, this system would contain a compressed air engine as well as compressed air tanks. Compressed air would be delivered to the engine, which would mechanically power an alternator that would recharge a battery. This battery would have to be smaller than the current battery in order to accompany the additional equipment. The compressed air tank would be located on a platform over the treads of the robot. The system would charge the battery until the fuel has run out, at which point the battery will begin to discharge at the normal rate. This method would increase the life of the system. A schematic of this system can be seen below in Figure 27.
The advantages of this concept are that it would greatly increase the life of the system. The disadvantage of this system is the large air tank size requirement. Packing problems might also occur with incorporating an engine and an alternator.
39
Figure 27 - Compressed Air Engine Concept
3.4.5 Concept 5: Internal Combustion Engine An internal combustion engine could be used to power the battery being used by the robot. This engine would run an alternator that would constantly recharge the battery. The battery size would be reduced to accompany an alternator and a small gas powered engine. All of these components would occupy the space that is currently taken up by the battery. A gas tank would be mounted on a tank platform above the treads of the robot. This would allow for a tank that could be as large as is allowable without increasing the payload of the robot to a point that becomes detrimental to the life of the battery. The system would charge the battery until the fuel of the engine ran out, at which point the battery would begin discharging as it normally does. Although the battery would be smaller and would therefore have less capacity, the power provided by the engine would greatly improve the life of the battery. A schematic can be seen below in Figure 28.
40 The advantages of this system are that the battery life would be greatly improved and the engine could possibly run off of fuel that is readily available in the field. The disadvantages are that there will most likely be added weight which could affect performance, and there may be some trouble with packaging the engine and alternator in a small area. If this is the case, an already integrated system such as a generator will need to be used. Most alternators or generators do not operate at the voltage that the TALON operates at, which would require voltage amplification or regulation as well as possibly having to convert from alternating to direct current in order to conform to the voltage requirements of the system.
Figure 28 - Combustion Engine Concept
3.4.6 Concept 6: Fuel Cell A fuel cell system could be directly used to power a battery in the robot. The fuel cell system would be powered by a fuel called sodium boro-hydride, which would eliminate the need for an external tank. This fuel is dumped directly into a tank that is integrated into the fuel cell stack. The entire stack would be
41 located on a mounting platform located above the treads of the robot and would deliver power to the battery. The fuel cell would charge the battery while it is running, increasing the life of the battery tremendously. A schematic of this concept can be seen below in Figure 29.
A major advantage of this system is the improved battery life. This system would probably provide the longest life out of any of the concepts. The disadvantages of this system are that there are not many products on the market that fit the specifications of the TALON robot. This may lead to problems with lead time and overall feasibility.
Figure 29 - Fuel Cell Concept
3.5 CONCEPT SELECTION The concept selection is based upon the seven most important design criteria. The design criteria are: time constraint, power density, maximum power output, battery life, volume, weight, and Foster-Miller input. In order to select the best concepts to test, two concept matrices were put together. The first, seen in Table 6, is a summary of the criteria of each concept, and whether they perform better or worse than the current systems. A plus sign (+) implies the concept exceeds the current power sources, a minus sign (-) means that it fails to meet the current standard, and a zero (0) mean it performs the same as the current sources or
42 is not applicable to the concept. The second, seen in Tables 7 and 8, rates each power source for all of the criteria on a scale, and then places extra emphasis on the most important design criteria.
3.5.1 Decision Matrices Table 6 - Concept Selection Matrix
From the first concept matrix it can be seen that an internal combustion engine is the best option available. This is due to the fact that it would greatly increase the power density and battery life of the system, while still providing the same or better capabilities in all categories. The second best option turns out to be lithium ion phosphate batteries, due to the fact that they provide a quick solution within the time frame of this project while maximizing the volume and improving the battery life.
43 Table 7 - Concept Selection Matrix 2 Part 1 Concept 1 Concept 2 Concept 3 Category Units Weight Value Weighted Value Weighted Value Weighted Capstone Time Constraint - 3.5 4 14 4 14 4 14 Capacity Wh/kg 5 2 10 2 10 0.5 2.5 Battery Lifehrs5315315420 Voltage Supplied V 5 5 25 5 25 2 10 Sizein341241200 Charge Time hrs 3 3 9 4 12 3 9 Robustness - 3 4 12 4 12 5 15 Water Tight/Dust Proof - 2.5 4 10 4 10 4 10 Weightlbs50 0 42015 Temperature Dependence ºC 2 2 4 2.5 5 4 8 Form of Power-5525525525 Max Power OutputW441641600 Foster-Miller Input - 5 0 0 3 15 0 0 Total 152 191 118.5
Table 8 - Concept Selection Matrix 2 Part 2 Concept 4 Concept 5 Concept 6 Category Units Weight Value Weighted Value Weighted Value Weighted Capstone Time Constraint - 3.5 3 10.5 4.5 15.75 1.5 5.25 Capacity Wh/kg 5 4 20 4 20 4 20 Battery Lifehrs5420420420 Voltage Supplied V 5 5 25 5 25 5 25 Sizein3003939 Charge Time hrs 3 3.5 10.5 3.5 10.5 3 9 Robustness - 3 3 9 3 9 1.5 4.5 Water Tight/Dust Proof - 2.5 4 10 4 10 4 10 Weight lbs 3 0 0 3.5 10.5 2 6 Temperature Dependence ºC 2 5 10 5 10 3 6 Form of Power-5525525525 Max Power OutputW4520520520 Foster-Miller Input - 5 5 25 5 25 4 20 Total 185 209.75 179.75 Using the weighted values for each concept the best concepts are slightly different. By rating the most important specifications it can be seen that the internal combustion engine concept is the best option. There are no real downsides to the internal combustion engine, as long as the device performs as expected. By analyzing the three matrices above, it becomes clear that the internal combustion engine concept is the most viable option. This is the concept that will be selected for further design and proof of concept testing.
3.5.2 Additional Concept Elimination Data By defining the minimum criteria required to run the TALON robot, several of the design concepts were eliminated mathematically. Several concepts were initially believed to be able to perform to higher levels than they were capable of.
44 3.5.2.1 Solar Panel
Solar panels were not believed to be able to provide the power necessary to run the TALON robot and this can be seen from the products that are available on the market. The most viable option for the TALON robot was the Uni-Solar Portable Solar Module UNI-PAC 30. The portable, and foldable solar panel set was rated at 34 watts at maximum output for a panel surface area size of 58 x 33.3 inches. The following calculations were performed to determine the minimum surface area needed:
800W 1ft 2 = 23.53*58in *33.3in = 45444.71in 2 * = 315 ft 2 (1) 34W 144in 2
This calculation shows that for the 800 watt power surge the TALON is capable of, it would require 315ft2 of surface area. This is clearly far too large to be a reasonable option for powering the TALON robot. This data does still support the possibility of using solar panels when the TALON is not in use, or for a minimal increase in battery life, but due to several other negative aspects, primarily Foster-Miller’s preference, the solar panel concept can be eliminated.
3.5.2.2 Compressed Air Engine
The compressed air engine from Engineaire, referenced in the background research, is a very small, very powerful engine. However, when the calculations for the required air tanks, and the rate at which air needs to flow to the engine to deliver such power, it becomes apparent that the compressed air engine is not viable for the TALON application. The air consumption at maximum power output is 167 cubic feet per minute, producing 4.6kW of power. The TALON requires approximately 0.8kW of power for 4 hours. The following calculation was performed to determine the minimum volume of air needed to provide the necessary power:
167cfm cfm cfm ft 3 60min = 36.3 ⇒ 36.3 ∗ 0.8kW = 29.04cfm ⇒ 29.04 ∗ ∗ 4hr = 6970.43 ft 3 (2) 4.6kW kW kW min 1hr
This shows that one would need approximately 7000ft3 of air to produce the power for the required time. This is much too high for the available space on the TALON robot. This is roughly equal to about 88 standard AL80 aluminum scuba tanks. This is clearly far too large for this application.
45 3.5.2.3 Nickel Cadmium Batteries
There have been significant advances in nickel cadmium batteries over the last few years, which were believed to have led to increased power density, and it was believed that there could be batteries on the market that could exceed the capabilities of both lithium ion and lead acid batteries. However, after an extensive search, it was found that this was not true. The volumetric power density of nickel cadmium batteries is better, the gravimetric power density of nickel cadmium batteries is only about half of what lithium ion batteries achieve. This means that while the nickel cadmium battery provides more power when they are the same size, the nickel cadmium battery would need to be much heavier. With weight being a serious concern for the end user, this eliminates nickel cadmium as a viable power source.
3.5.2.4 Fuel Cells
It can be seen from the data and concept decision matrices that fuel cells are a viable concept. However, Foster-Miller has been working with Protonex, a local company on developing a a customized fuel cell system. Due to this work, the concept of using a fuel cell for the TALON robot will not be pursued any further.
46 CHAPTER 4 DESIGN AND ANALYSIS
4.1 DESIGN OVERVIEW
As stated in Chapter 3, an internal combustion engine system was concluded to be the most effective to run the TALON. The original plan for this project was to test both the Honda Generator as the internal combustion system, and the lithium ion phosphate batteries to compare them to the current power output of the lithium ion and lead acid batteries used by Foster-Miller. This information can be found in Appendix A. Once the internal combustion engine was chosen, another department at Foster-Miller was brought into the project and introduced a small aircraft engine. The goal of the project then became to integrate this smaller engine into the TALON and design a system to ultimately run on gasoline.
As discussed earlier, the system will be run by charging a battery using a small internal combustion engine and a motor run as a generator. The engine runs on gasoline, which has a much higher power density than any battery system. The system is more user friendly, requiring only the gas tank to be refueled instead of having to charge the battery for hours at a time. There are several design issues with the system. The first is starting the system.
An internal combustion engine requires the use of spark plugs to ignite the fuel during the 4-stroke process. This means that the battery must first start the engine through the spark plugs and the motor, and then as soon as the engine is running, it begins to be charged by the generator.
The internal combustion engine system for the TALON robot will consist of numerous components all critical to increasing efficiency of the robot. There are seven major parts to the system, each with several components. The system consists of the engine system, starter/generator, cooling system, fuel tank, batteries, mounting plate and the system housing. The following section discusses each of these components in depth as well as explains what each component is for, as well as how they were designed or selected.
4.2 ENGINE SYSTEM
4.2.1 Internal Combustion Engine The engine that was selected is the Saito 60 Twin Cylinder ABC engine, shown in Figure 24. This engine is a four-stroke, two cylinder internal combustion engine with almost all the necessary components built in. The engine includes two flat cylinders to maximize the space available on the TALON. The engine can run
47 from 2,000 – 10,500 rpm, which meets the requirement of the engine needing to run from about 7,500 – 8,000 rpm to meet the demands of the generator. The generator will be introduced in Section 4.3. The engine is rated to produce .9 hp. This engine was selected because it meets the size, power, and feasibility needed for the system.
Figure 30 - Saito 60T Twin Cylinder Engine [38]
4.2.2 Ignition System
The ignition system, shown in Figure 31 is a standard off the shelf item purchased from CH Electronics, Inc. The ignition system was chosen because it is small and lightweight. The ignition is a spark plug with a magnet and hall-effect sensor. The magnet has to be placed in front of the sensor while the pistons in the engine are at a position called "top dead center", so that the spark occurs at the exact moment needed to ignite the fuel in the cylinder to drive the piston. The engine currently ignites the fuel using glow plugs, which stay hot enough from the previous explosion to keep the pistons firing. The problem is that the glow plugs can be disconnected from their power source too early, which causes the engine to shut off. Installing a spark plug ignition makes the engine more reliable and uses far less energy.
48
Figure 31 - CH Electronics Ignition System
4.2.3 Carburetor
An integral part in converting this engine to handle gasoline as a fuel rather than the glow fuel that it is designed for is to choose and install a new carburetor that is designed for gasoline. With input from Foster Miller, the carburetor chosen for future integration is the Walbro WT-38B carburetor, shown in Figure 32. One of the main characteristics that made this carburetor so attractive is that it has a built in fuel pump. Other advantages of this carburetor are that it has the equivalent of a float chamber incorporated into it, it has a widely adjustable main jet, and its reliability has been proven in previous Foster-Miller tests.
Figure 32 - Walbro Gasoline Carburetor
Since this carburetor was not designed for this engine, an adapter must be used to integrate the carburetor.
4.2.4 Carburetor Adapter Block
This part also had to be designed specifically for the internal combustion engine system to run on gasoline instead of model aircraft fuel. Currently, the engines are sold with a carburetor factory isntalled. For this project, that standard carburetor was removed and the airflow was redirected from the engine through the
49 connector block to the Walbro Carburetor detailed above. This connector block is an aluminum block that attaches to the engine on one side and the carburetor on the top with a cylindrical passage hallowed out. This allows the carburetor to be mounted at a 90 degree orientation to the engines air intake, which is crucial for space reasons within the system housing.
4.2.5 Muffler
To determine the displacement of the plenum inside the muffler needed for this application, a general rule is applied in which the displacement of the plenum must be ten (10) times the displacement of a single engine cylinder. The cylinder displacement in the Saito 60T is 0.6 in3, therefore, giving us a single cylinder displacement of 0.3 in3. This means that the displacement of the plenum must be equal to 3 in3. Next, the diameter and length of the plenum must be found. Figure 33 shows the relationship between the diameter and length with a total plenum volume of 3 in3.
Muffler Size Chart 3 in3 Displacement 18
16
14
12
10
8
6 Length of Plenum (in) Plenum of Length
4
2
0 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 Diameter of Plenum (in)
Figure 33 - Muffler Size Chart
Using this chart, a diameter of about 1 inch and length of about 4 inches would be a viable option. The next step was to find standard sizes of aluminum piping and tubing. There is a standard aluminum pipe size of
50 1.049 inch ID and 1.315 inch OD that could be used that would need to be cut to a length of 3.471 inches to create the necessary plenum displacement. [39] This is shown in Figure 34.
Figure 34: Inner Tubing of Muffler
After this pipe was sized, a standard size of .19 inch ID and 0.250 inch OD copper tubing was found to vent exhaust from the plenum. This tubing was coiled around the aluminum pipe then opened up to the atmosphere to expel the exhaust. By summing the copper tubing OD with the OD of the aluminum plenum, the new outside diameter of the system would be 1.815 inches. [40] This is shown in Figure 35.
Figure 35: Inner Tubing with Aluminum Piping
The next step was to find an aluminum pipe to enclose the system. The closest standard size found was 1.884 inch ID and 2.000 OD and is shown in Figure 36. [39]
Figure 36: Muffler with Outer Casing
The final step was to cap off the ends using 0.125 inch thick aluminum plates, as shown in Figure 37.
51
Figure 37: Final Assembly of Muffler
The overall dimensions of this muffler assembly would be 2.000 inches in diameter and have a length of 3.721 inches.
Two inlet holes were drilled in the front face of the muffler. These holes were placed symmetrically around the center line of the face at 0.45 inches apart with a diameter of .0125 inches. These holes allow for the muffler outlet of the engine to direct the exhaust into the muffler for sound attenuation. A single hole was drilled into the back face and a small nozzle was attached to exhaust any fumes.
4.2.6 Air Silencer
In order to cut down the noise levels as much as possible, an air silencer was selected to attach to air intake of the carburetor. The device that was selected was Compact Air Intake Filter/Silencer from McMaster- Carr, shown in Figure 38. This device was chosen because it was compact and attenuated 5 – 15 decibels of sound while also filtering particles as small as 2 microns. This device is only 2-1/8 inches tall with a 2 inch diameter, allowing it to fit onto the carburetor without taking up valuable space.
Figure 38: McMaster-Carr Air Intake Silencer
4.3 Starter/Generator
The means of generating electrical current is through the use of a motor. When normally run, this device would be electrically powered by a battery, to run a drive shaft. In this case, for generating electrical current, the motor is run in reverse and is driven by the torque output of the internal combustion engine. The current and voltage output are specific to the type of motor used. The motor outputs a DC voltage, rather than most generators that output AC voltage for commercial electrical equipment. The DC motor that
52 is being used is the Cobalt 60 Direct Drive Brushed Motor. This motor was selected because of its size, voltage and current range, and can be seen below in Figure 39.
Figure 39: Cobalt 60 Direct Drive Motor [41]
The motor is 3 inches in length and 2.1 inches in diameter and weighs only 1.375 lbs. The shaft diameter is 0.25 inches. When run in typical motor applications the device can generate up to 1000 watts of power between 24 and 48 volts. Each motor can be customized in order to produce the proper amount of voltage, and this model had to be customized into a 36 volt system. This voltage can be attained by setting the voltage constant, Kv to the proper level. The voltage constant is a value that determines what voltage will be output, based upon the motor speed. For this particular application the shaft would be rotating at around 8,000 RPM. This would require that the voltage constant be set to 222.2 RPM/volt.
4.4 Cooling System
The most significant engineering problem with the implementation of an internal combustion engine is the cooling of the engine and several of its components. The mechanical motion of the internal cylinders, can generate heat on the level of about 300ºF, which greatly depreciates the life of the system. Normally, with the engine that has been selected, the cooling would be provided during the normal use of the system. The Saito 60T is specified for a small hobby airplane engine, which would be exposed to the open air. During flight the engine would be exposed to high speed winds that provide a natural cooling system. For this design, the engine will be used in a ground vehicle traveling at low speeds and will also not be exposed to the outside air. For this reason an oil cooling system was designed. Each of its components is discussed in the following section.
53
4.4.1 Oil and Pump
In order to provide cooling to all the necessary parts, a fluid and means of transporting that fluid had to be selected. Oil was selected as the cooling fluid for its viscous properties as well as its ability to also act as a lubricant during future advanced cooling plans.
To select a pump, both its size and its capabilities were considered. The pump must be able to fit into the limited area available, and provide the proper flow rate to induce cooling of the external parts. The following is a calculation for flow rate based onthe amount of heat that will be wasted through the cylinders:
Qwaste w f = c p,oil (Thot − Tcold )
woil Q f = ρ oil
Q f = 3.7gph
It can be seen that the pump would have to provide around 4 gallons of flow per hour. This is a very low flow rate compared to most pumps on the market. To fill the needs of the system the Greylor PQ-12/24 positive displacement pump was selected. This pump provides a minimum of 5 gallons per hour, but can provide up to 35 gallons per hour. The pump weighs only 0.833 pounds and measures only 3 inches in length and 2 inches in diameter. The pump operates on direct current, so it can be powered from the motor/generator.
Figure 40: Greylor PQ-12 Oil Pump [42]
54 4.4.2 Oil Jacket
The most logical area for cooling is the fins on each of the cylinders of the engine. This area generates the most heat during the mechanical motion of the engine. The jacket that was designed contains two pieces; a top and bottom half. Each side is symmetrical and is interfaced with the top of the fins. When fastened together around the fins, the jacket allows oil to enter through the top hole into a manifold that distributes the oil to six different smaller holes corresponding to the gaps between each of the fins on the cylinder. This allows the oil to pass over the cylinder at high speeds, removing heat from the engine. The central plenum is not drilled all the way through to line up the edge with the inner most fin, while the holes interface with the cylinder. This ensures alignment with each of the fin gaps.
Figure 41: Oil Jacket Assembly
Another design challenge was how to keep the oil jacket in place so that the holes were properly aligned with the gaps between the fins. The way around this was to use an aluminum tube with a smaller inner diameter. This would allow a small hole to be machined out of the rod stock and then a larger hole to be machined out up to the area where the fins begin. This creates a sort of edge on the jacket for alignment with the first fin.
The engine cylinders themselves have a connected area where the oil would not be able to flow through since they are not a complete open circle around the engine. The oil flow would stop when it reaches this point instead of dripping out of the bottom of the jacket. These areas had to be machined out of the engine to allow the oil to flow completely around the cylinders from top to bottom.
4.4.3 Heat Exchanger
The heat exchanger that was selected was a parallel flow, shell and tube heat exchanger.
55 Based on previous heat exchanger designs by Foster-Miller, it was concluded that a 3” by 3.5” by 1” thick heat exchanger would be more than sufficient to work to cool the proposed system, as shown in Figure 42. The heat exchanger consists of 10 straight aluminum “ribbons”, 3 inches long in the oil flow direction. These ribbons carry oil in 21 small channels inside each ribbon. The ribbons are spaced .25 inches apart and the space is filled with 6 millimeter thick aluminum fins spaced at 8 fins per inch. These fins are vacuum brazed to the aluminum ribbons. Air flow over the fins and cools the aluminum, which in turn cools the oil.
Heat Exchanger Selection
12
10
8
6 Width (in) Width 4
2
0 024681012 Length (in)
Figure 42 - Heat Exchanger Selection
4.4.4 Cooling Fan
Sizing the fan for the heat exchanger to achieve the desired cooling can be done after the size of the heat exchanger has been finalized. The size of the heat exchanger is 3.5 inches square. This means the fan’s maximum size would be 3.5 inches in diameter. Knowing this, the next step would be to calculate the required air flow rate needed for the heat exchanger to work properly. To figure out how much air flow we need through the case to get adequate cooling, the following equation was used, where Q is in the power, in Watts, made by the engine (250 W), is the mass flow rate of air being circulated (desired number), cp is the specific heat or air at atmospheric pressure and 250°F, (1013 J/kg°K) and ∆T is the change in temperature desired (250-200°F).
56
Plugging these numbers into the equation, works out to be 0.5331 . Now air at 250°F has a density of
.0254 , so the desired fan rating would need to be 21.6 cfm.
Since there are other components within the enclosure that will operate more efficiently with air flow over them, including the oil pump, engine and muffler, a fan from McMaster-Carr was chosen that has a cfm double of what we need that is 3 inches by 3 inches. This fan is seen in Figure 43.
Figure 43: Cooling Fan
4.5 Fuel Tank
A 16 ounce fuel tank was found and chosen due to the fact that its shape could be molded slightly with a heat gun. With such tight space constraints, the ability to reshape the fuel tanks could be critical in allowing all components to fit within the design.
Selecting the size of a fuel tank is a balance between run time for the engine and available space given for packaging. Given that this project has such tight space requirements, the fuel tank chosen for this application was a 16 ounce Flextank from Sullivan Products, shown in Figure 44, and made out of a translucent polymer that can be reshaped with a heat gun. The reason this capability is desired is that if we run into space constraints, we can easily customize the tank to fit where it is best suited.
57
Figure 44: Sullivan Products 16oz Fuel Tank [43]
4.6 Batteries
For this system, three 12 volt lead acid batteries were chosen. There needs to be three to allow them to be hooked up in series to equal 36 volts.
After electrical power leaves the generator, it is transferred to a set of batteries. These batteries will then transfer power to the TALON’s electrical systems. These batteries will handle the power fluctuations that the robot will experience. Additionally, the batteries are designed to run the TALON without the engine in operation, for situations where either the engine fails or silence is critical. Foster-Miller has expressed a desire for 20 minutes of run time on battery power alone, given the space constraints of this application. With a 200 watt power draw at 36 volts, a simple calculation shows the selection process for the batteries.
P = i *V P i = V 200W i = = 5.5amps 36V C = i *t
C = 5.5amps *.3hrs = 1.85AmpHours(AH )
Using this calculation, and with the size restraints of the housing, the UB1250 CAM from SafeMart, shown in Figure 45, was selected. This as 12 volt battery rated at 2 amp-hours, with dimensions of 5.63 L x .83 W
58 x 2.50 H in inches. Three of these batteries will be connected in series to achieve the 36 volt need of the TALON.
Figure 45: 12V Lead Acid Battery Pack [44]
4.7 Mounting Means
In order to directly drive the starter/generator from the engine, a mounting plate was used. This mounting plate served as an integral part of the design. The mounting plate was designed from a standard piece of U- channel 6061 aluminum. The piece was then modified to fit into the housing while still allowing the starter/generator and engine to be mounted. The plate is shown in Figure 46.
Figure 46: Engine and Starter/Generator Mounting Plate
59 From the previous figure, it can be seen that there are two mounting areas. The right hand side is for mounting the starter/generator and the left hand side is for mounting the engine.
The starter/generator required five holes to be drilled in order to facilitate mounting. Four of these holes are for securing the device to the plate, the fifth hole is to allow the engine shaft and starter/generator shaft to interface. The mounting holes are 0.125 inches. Four screws are used to secure the starter/generator. The shaft hole is 0.3 inches in diameter.
The engine uses a separate bracket to interface the engine with the mounting plate. This bracket attaches to four points on the engine, and four points on the mounting plate. Four holes were tapped in the mounting plate, each 0.16 inches in diameter. The bracket was then secured to the engine with four hex socket cap screws, and to the mounting plate with four hex head screws. These brackets are shown in Figure 47.
Figure 47: Engine Mounting Brackets
In order to ensure that the strength of the mounting plate was sufficient analysis was conducted. The two major forces that would appear on the plate would be a torsional force from the rotation of the engine shaft, and also the overall effect of the weight of the engine and generator on the plate.
4.7.1 Structural Analysis
The only component that would see any significant forces is the mounting plate used for coupling the engine and DC motor. As the system is running, the motion of the shaft creates a torque force on the mounting means of the DC motor. From the following calculation the estimated torque force was determined:
60 2πTω (2π )T(8000rpm) P = ⇒ .25kW = ⇒ T = 0.298Nm 60000 60000
Using this torque value, computer aided analysis was conducted. The analysis would be used to determine if the mounting plate would fail under the given force, as well as determine the maximum deflection that the mounting plate would see. It was predicted that failure of the mounting plate was unlikely, but the deflection of the mounting plate could result in unaligned coupling of the engine and DC motor shafts. This deflection would result in significant efficiency losses of the system.
Analysis was conducted using the design and analysis programs in SolidWorks. Figure 48 shows the areas of stress. Figure 49 shows the maximum deflection of the mounting plate.
Figure 48 – Stress Distribution Figure 49 - Maximum Deflection
The maximum stress on the mounting plate was 1.2*106 N/m2 and the maximum deflection was 0.0006in. The deflection of the mounting plate was marginal. To determine the margin of safety for the mounting plate, the following calculation was completed:
Allowable_ Stress 55*106 M = −1 = −1 = 45 s Actual _ Stress 1.2*106
A margin of safety of 45 was more than sufficient for the design to function properly. This analysis eliminates any concern of material selection or torque force.
61
4.8 Housing
The housing design was based on the current lithium ion battery housing, but with several modifications to maximize available space and also to facilitate the overall use of the engine system. The housing was made of vacuum formed thermoplastic, which provides sufficient material strength and temperature dependence. The housing has two separate pieces; a lipped bottom and a top that firmly interfaces with it. Further design will be required in Future Work to fully define the aesthetics and manufacturing of the case.
The space between the arm of the TALON and the battery housing when in stored position was examined more closely. A ramp was added to the middle of the housing which allowed the engine to be rotated to make way for a directly driven generator as opposed to the initial design of the belt driven system. Figure 50 shows the housing.
Figure 50: System Housing
With the internal combustion engine system air needs to enter near the cooling fan and circulate over the muffler for extra cooling. This warm air then needs to exit the system. To induce airflow, it was necessary to create a proper airflow within the system to avoid overheating. A schematic of the airflow is shown in Figure 51.
62
Figure 51: Air Flow Diagram
The goal of the air slots on the top left and right of the housing is to force the air to exit on the left side above the muffler by making those be the only possible points of exit. Outlets were also included for the TALON interface and carburetor air intake.
4.9 BILL OF MATERIALS
The bill of materials (BOM) is included in Table 9. This bill of materials is for all the components that were designed for testing and verification of the system, with the 36 volt system in place of 12 volt components. The BOM includes each component, its quantity, whether it is a machined or purchased part, and the prices of all parts that are available.
63 Table 9 - Bill of Materials
4.10 Assembly
Assembling the system within the design constraints was one of the most critical parts of the design process. If the components could not be fit into the housing then the system would be worthless. Figure 52 shows the proposed configuration of the system.
64 6 3 5 7 2 4 8 1
9 17 12
13 10
16 11 14 15
Figure 52 - Final Design Layout
From this figure it can be seen that the critical engine parts are placed in the left section of the housing. This eliminates and fluid from contacting electrical components. The heat exchanger and fan are secured to the top of the right side of the housing to draw air through the vents. All other components were placed in areas to maximize space. Each component is identified by number in Table 10 below.
Table 10: Table of Component s
65 CHAPTER 5 TESTING
The testing of the internal combustion engine was approached as a proof of concept study. Standard off the shelf parts were selected to run the system at 12 volts. Once it was proven to Foster-Miller that the system would operate as designed, the custom 36 volt parts could be ordered.
The first step was to prepare the test set-up. The engine and generator were mounted to the mounting plate and connected via a Lovejoy zero backlash flexible spider shaft coupling. This coupling was wrapped with electrical tape and two hose clamps for securing and balancing the system. Next, the muffler was connected to the cylinder exhaust through two flexible hoses. The fuel tank was filled with “Glow Fuel”, which is a mixture of methanol, nitromethane, and oil, and connected to the carburetor. Additionally, a syringe was filled with fuel and used as a primer. The glow plugs were connected to a DC power supply in order to heat them up. The generator output wires connected to two 6 volt batteries in series to match the 12 volt output. These batteries not only provide power to start the engine, but are then charged by the generator when the engine is running. The output of the generator was also connected to a volt meter and a load bank. This load bank provided resistance to test the amount of power the generator was producing. A fan was mounted on a stand and placed over the cylinders to prevent overheating, and a thermocouple was inserted into one cylinder of the engine to monitor the internal temperature. If the internal temperature of the engine were to exceed 350oF the engine would be shut off. The test set-up can be seen in Figure 53.
66 Load Bank Fuel Tank Fan
Muffler
DC Power Supply Thermocouple
Volt Meter
Batteries Engine & Generator
Glow Plug Syringe
Figure 53 - IC Engine Test Set-up
To start the engine it was first primed, and then the negative and positive terminals coming from the generator were connected to the negative and positive terminals on the battery. The throttle was adjusted and the engine started. To prove that the engine was running under its own power, with no help from the batteries, the generator output was disconnected from the batteries and connected to the load bank. The engine continued to run proving that the concept works.
Various loads were put on the engine to test the output wattage. By measuring the voltage and knowing the amount of resistance of each load, the output wattage could be determined. These power outputs can be seen below in Figure 54.
67 Power Output of Generator
100
90
80
70 Power (watts) Power
60
50 00.511.522.5 Resistance (Ohms)
Figure 54 - Power vs Resistance Graph
A tachometer was used to measure the speed of the engine which showed that the engine was running between 7500 and 8000 rotations per minute (rpm). It can be seen that the generator was putting out about 75 watts at 7500 rpm. The generator was configured to be 85 percent efficient and put out 200 watts at 7500 rpm. This shows that the generator was not as efficient as rated.
Pelec = 75W
Pmech = (2π )(T )(RPM )
T = kt I = (3.61) *(6.25) = 0.1176 ft − lbf
Pmech = 125.22W 75 η = = 59.9% actual 125.22
ηclaim = 85%
P = (.85) *(125.22) = 106.4W
At the measured RPM the shaft output should have been 125.22 watts. With an 85% efficiency, the power output should be 106.4 watts. However, the generator was only producing 75 watts, giving it an efficiency of 59.9%. It is clear that the generator is not performing as specified. Replacing the generator would most likely produce better results, and is believed to be the key inefficiency of the entire system.
68
It was also proven that the oil jacket was needed. The engine is normally cooled by running it on a plane that has air passing over fins on the cylinders at 60 miles per hour. The small fan used was enough to keep the engine cool long enough to record the power data; however air did not cool the engine enough to run continuously. Again, as a proof of concept, it was proved that the engine would run a generator that would produce electrical power. Now that the results are positive, the oil jacket will be manufactured just as the 36 volt custom parts will be ordered.
69 CHAPTER 6 CONCLUSIONS & FUTURE WORK
6.1 Conclusions The grand scheme of this project was to identify a better alternative to the current power systems of the TALON robot. Through thorough research, interviews, and analysis of power systems it was determined that an internal combustion engine system was the best option. It provides significantly higher power densities than batteries and has the capability to provide electrical power through the use of a motor, while still fitting in the allowable space.
The design of the system consisted of selecting commercially available parts, including the pump, cooling fan, batteries, motor, engine and fuel tank. It also involved designing a cooling system, heat exchanger and housing unit.
The testing of the generator system was a success. The internal combustion engine coupled to a generator produced electrical power. The power output of the TALON was consistently 75 watts. The system could not function for more than a few minutes due to overheating, which verifies the need for a cooling system. The sound attenuation devices properly dampened the noise produced by the system. While this power was no sufficient enough to power the TALON at this time, the design of this system was a significant step towards the full integration of a gasoline power system.
Foster-Miller’s intention with this project was to prove that the system could work within the space allotted. From the successful design and testing of the internal combustion engine system, Foster-Miller will move forward with this project on their own, using the design and testing provided in this report.
6.2 Future Work
There are still many improvements that could be made to the new system. The purpose of this project was to prove that an internal combustion engine driven system would work, but not that it would outperform the current system. There are many improvements that can be made to extend the life of the robot and the ease of use for the end user.
The first step will be to convert the engine to a gasoline system. This will be an integral step in greatly improving the run time because of the great power density of gasoline compared to glow fuel. Included in converting the system to gasoline are installing the gasoline carburetor, the adapter block and installing the ignition system and spark plugs.
70 Increasing the life of the system is dependent upon the cooling system as well. Because of manufacturing times, the cooling system was not able to be manufactured. The cooling system discussed in the design chapter will have to be used, and a heat exchanger will need to be custom made in order to prove that it increases the life of the engine. Oil recovery will have to be taken into account, in order to reduce user maintenance.
While testing was conducted on a 12 volt system, this is not the system that will be used. Future testing will have to be done on the 36 volt system that the TALON must use. This involves only changing out the batteries and the starter/generator, which are currently 12 volt, and replacing them with the 36 volt equivalents. This should increase the performance of the electrical systems, but must be verified. The starter/generator is currently a brushed DC motor. While these motors are sufficient, a brushless DC motor would provide a more powerful and efficient system. This system, however, requires a very complicated voltage control system, which would need to be designed.
For this project, it was not necessary to fabricate the housing of the system. This housing will need to be designed with the user in mind. Easy access to fuel tanks, oil cooling system and the ignition system will be critical. This housing will also need to be adapted to interface with the TALON electrical systems. This fabrication of the housing will be conducted much later in the design process, as it will be designed with the completed final design in mind.
71 WORKS CITED
[1] “TALON Military Robots, EOD, SWORDS, and Hazmat Robots.” Online. 11 September 2007
72 [27] Blenke, Joseph F.; Blenke, Stanley J.; Air Power Motor, US Patent 4,355,508, to US Foam Mfg. Co., Inc, Patent and Trademark Office, 1982. [28] Zheng, Yongjian; Monolithic fuel cell and method for manufacture of same, US Patent 6,838,203, Patent and Trademark Office, 2005. [29] Smits, Johannes G.; Integrated micromechanical piezoelectric motor, US Patent 5,049,775, to Boston University, Patent and Trademark Office, 1991. [30] Miyazawa, Osamu; Micro Robot, US Patent 5,554,914, Patent and Trademark Office, 1996. [31] Stang, John H; Cusick, Steven M..; Oil cooled internal combustion engine, US Patent 4,440,118, to Cummins Engine Company, Inc., Patent and Trademark Office, 1984. [32] “iRobot PackBot EOD.” 13 September 2007.
73 APPENDIX A
DESIGN OVERVIEW Internal Combustion Engine System
As explained above the internal combustion engine system will be used to run an alternator, which will charge a battery during its normal operation. Most small engines are run at either 1800 RPM or 3600 RPM when used with an alternator. Applications for most 3600 RPM engines are high output with less concern about size and noise. Applications for 1800 RPM motors are normally ones in which noise and size are major factors. The most suitable engine for this application would be an 1800 RPM engine.
In a standard belt driven alternator, the gear ratio is normally around 3:1, depending on the application, which can be seen below in Figure 30. This means that while the engine shaft would be running at 1800 RPM, the alternator shaft will be turning at about 5400 RPM. The current produced by the alternator is a function of this rotational speed, and is varies between alternator type. Most car alternators need much more current that that of the TALON robot, due to shear size and features. Therefore an alternator must be selected that can produce about 20 amps at 36 volts, an application which is typically not seen.
Figure 30 - Alternator Belt Ratio
In order to simplify this system a generator will be used. This generator consists of a compact gas tank, engine and alternator. Through an extensive search several viable generators were found that provided the proper power. Through several interviews with both Foster-Miller and field experts the appropriate equipment was selected. The results of this search can be seen in Table 9.
74 Table 11 - Generator Search Results
Rated Power Maximum Power Weight Run Time Company Fuel Type VAC VDC (watts) (watts) (lbs) (hrs)
Kipore Sinemaster Gasoline 900 1050 30.8 5 120 12
Pramac Pi1700 Gasoline 1350 1650 45 3.5 120 12
Briggs & Stratton 900W Gasoline 900 1000 55 3 120 12
Yamaha EF1000iS Gasoline 900 1000 27 3 120 12
Honda EU1000i Gasoline 900 1000 29 3.8 120 12
Eng Tech 0141 JP-8 750 - 50 4 120 12
Eng Tech 0101 JP-8 1250 - 50 4 120 12
From this table it can be seen that the best weight to power ratios come from the Kipor Sinemaster and the Honda EU1000i, which are each around 30 lbs. The Kipor Sinemaster however, claims to run for 5 hrs at the rated current. This makes it the best available generator on the market. Unfortunately, the Sinemaster is not as accessible as the EU1000i. The Honda EU1000i, can be found locally in Watertown, MA. Dimensions have been taken in order to design an adapter plate, and possibly a housing for the entire device. The Sinemaster will be tested if attaining a sample product is possible.
Figure 31 - Honda EU1000i Portable Generator
The generator that will be used can seen above in Figure 31. This is a commercial generator intended for portable power of electronics, generally in outdoor situation where no power grid is accessible. This makes the generator the perfect choice for the TALON application. The Honda generator is both quiet and lightweight. It weighs 33 lbs with fuel and produces a noise level of only 59dB at 7 meters when running at
75 rated load. This puts the noise level on par with the volume of a normal speaking voice for comparison. The Honda EU1000i generator holds 0.6 galls on gasoline fuel, and will run for almost 4 hours off of this tank. It also features a pull start motor. Most importantly the generator produces 900 watts of power at rated current load, which satisfies the minimum requirements of the TALON electrical systems. The rated load of this generator is 7.5 amps, and the TALON nominally draws around 6.5 amps. The run time of the generator at the rated wattage can be used to estimate a run time for the TALON. The run time of the generator at 900 watts is 3.8 hours. The TALON nominally draws 250. The following calculation estimates the run time of the TALON with a generator as its power source.
250watts 1 = .27778 ⇒ 3.8hrs * = 13.68hrs 900watts .27778
This load is delivered at 120VAC, which is not compatible with electrical systems of the TALON. Therefore, the voltage must be rectified and reduced to 36VDC. To do so, a voltage rectification system must be used. An extensive search was conducted using the aid of electrical engineers at Foster-Miller, and the proper equipment was selected. For this application, the best suited equipment was the V-Infinity VPM- S800-36R(I)-N Switching Power Supply. This device accepts a full range of AC inputs, and outputs a voltage from 27-36VDC. This still allows for a 800 watt power output, which meets the surge power rating, and greatly exceeds the nominal power rating of the TALON. The switching power supply can be seen below in Figure 32.
Figure 32 - V Infinity AC to DC Converter
Because of the slightly larger than expected size of the generator, the TALON side rack will be utilized. This rack will allow the generator and converter to be housed, while the battery can be as large as possible,
76 without become detrimental to the power capabilities. This will also protect the gas tank from outside damage, improving the safety. Extensive design of the housing is discussed in further chapters. Extensive analysis of the weight considerations on the rack are discussed in further chapters.
In order to minimize damage to the generator and AC to DC converter they will need to be mounted in their corresponding locations. This will require the design of mounting plate to facilitate the attachment of the components to the TALON. The design of said mounting plates are discussed in further chapters
Lithium Ion Phosphate Battery
As described in the concept previously, the lithium ion phosphate battery will replace the current battery systems once testing has been verified. Through communication with experts in the field and an extensive product search the lithium ion phosphate battery by A123 was selected as the only feasible vendor for this design. The battery packs, which can be seen in Figure 33 come individually and are placed in both series and in parallel to generate the required 36 volts. The batteries are then packaged in a housing and wired into the electrical system. A123 lithium ion phosphate batteries have an energy density of 3000 W/Kg and have a long shelf life.
Each individual battery is sized at 2.5 inch in length and 1 inch in diameter, for a volume of 2.5in3. Currently, the largest volume available inside the existing battery casing is just over 300in3, this would allow for 120 batteries. The batteries would be set up with 10 sets of 12 batteries in parallel.
Figure 33 - Lithium Ion Phosphate Batter from A123
The TALON robot needs to run at 36 volts, and each A123 battery is 3.3 volts. This means that through the simple parallel and series circuit, 36 volts can be achieved. With the higher energy density in the same volume, these batteries will have a longer running time than the current system.
With a power density of twice that of regular lithium ion batteries, the estimated running time of this battery would be just about twice as long as the TALON currently runs, or about 8.4 hours. If this system
77 were to be used with the internal combustion engine system, the estimated running time of the entire system would be about 12 hours.
The lithium ion phosphate design is a relatively simple design that could serve two purposes, depending upon testing results. Lithium ion phosphate has shown to be an improvement on the current lithium ion batteries, and may be able to replace the current batteries altogether. Also, if this battery proves to be better than the current power sources, and the internal combustion engine system also fulfills its potential. Theoretically, the best design would be an internal combustion engine that recharges a lithium ion phosphate battery. This will be tested in the test plan laid out in the following sections.
BILL OF MATERIALS
For each design there is a separate bill of materials that lists all the necessary components that will be used for the testing as well as initial mounting and housing. Tables 10 and 11 represent the bill of materials for the lithium ion phosphate battery setup and the internal combustion engine setup.
Table 12 - Lithium Ion Phosphate Bill of Materials Machined Part or Vendor/ Number Level Part Name Quantity Purchased Manufacturer Cost
Lithium ion $120/ 6 26650 nanophosphate cell 120 Purchased A123 Systems cells
Plastic Housing 1 Purchased Foster-Miller In Stock Subconn/ Foster- Power cable, female MCIL16F 1 Purchased Miller In Stock Subconn/ Foster- Power cable, male MCIL16M 1 Purchased Miller In Stock
78 Table 13 - Internal Combustion Engine Bill of Materials Part Machined or Vendor/ Number Part Name Quantity Purchased? Manufacturer Material Cost
EU-1000 Honda Generator 1 Purchased Honda $800
Rack 1 Machined Foster-Miller 6061 T6 In Stock
Adapter Plate 1 Machined In House/ NU Delrin from McMaster $12.28 for 1' x 2' sheet Hex Head Cap Screw, 1/4"- 92865A938 20 x 5/8" long 8 Purchased McMaster Zinc-Plated Steel $4.20/ 100 pack
VPM-S800- AC to DC Converter 1 Purchased V-Infinity $290 Subconn/ Foster- MCIL16F Power cable, female 1 Purchased Miller In Stock Subconn/ Foster- MCIL16M Power cable, male 1 Purchased Miller In Stock
Fuel 0.6 Gal Purchased Lukoil $1.58 NEMA 5-15/ IEC 320 Power 71535K66 Cord 1 Purchased McMaster $15.84
ASSEMBLY Housing
When using explosive fuel in an application like the TALON will be used, some concern must be put towards the protection of the power system. This will stop any damage to the system that could render it immobile or could cause sever damage from a fuel explosion. Therefore a secure housing must be designed to prevent such actions.
When designing a housing on a generator, there are several concerns. The generator uses an internal combustion engine which draws air in from the outside environment. It also dumps exhaust constantly to the outside environment. Fuel must be added to the generator, and the generator starters must be accessible in order to initiate generator use. The housing must be design with all specifications in mind.
Due to the necessary ventilation required for the generator, Foster-Miller decided that for a proof of concept test, a housing would not be necessary for the generator. The generator already contains the necessary housing for weatherproofing as possible. When the concept has been proven, packaging and housing will become more of a concern.
79 Mounting
In order to attach the equipment to the side platform an intermittent mounting adapter plate will be needed. This plate will allow the generator to be mounted to the plate, and the plate mounted to the platform. The drilled holes of the TALON rack do not match up with the feet of the Honda generator. Therefore, the following diagram shows the adapter plate designed to allow for mounting.
Figure 34 - Mounting Plate
The mounting plate is 20 inches by 9 inches and is made of Delrin plastic. This plastic is lightweight and rigid, and fully capable of providing the strength needed to mount the parts together. The mounting plate has four threaded ¼-20 thru holes. The mounting plate is then securely screwed to the rack.
The generator is secured to the mounting plate with the four interior thru holes. These thru holes are ¼-20 threaded with a counter sink. This counter sink will allow for the screws to be threaded in from the bottom, without interfering with the rack. These thru holes can be seen in Figure 34. The final assembly of the mounting plate system is shown in Figure 35.
80
Figure 35 - Mounting Plate Counter Sink
In Figure 36 it can be seen that the Foster-Miller platform will be the base of the mounting means. The mounting plate will be placed on top and secured to the platform, the generator will then be mounted to the plate. The four screws are shown as well.
Figure 36 - Exploded Assembly of Mounting Means
81 FUTURE PLANS
Moving forward with the design of the power system for the TALON robot, there are several critical tasks to be completed. The first is to get testing approved and complete the testing. Once the test plan is approved parts can be ordered and the test can be set up. After testing, a thorough analysis of the data will be conducted and conclusions will be drawn. These results will be communicated back to Foster-Miller and a plan of action will be established. The following is a detailed account of the testing that will be conducted on each power source. It includes a test purpose, test equipment and test setup.
TESTING
In order determine the best possible power source for the TALON robot, extensive testing must first be completed. This testing will be conducted to verify the performance of the current batteries in order to establish a baseline under the test setup conditions. Further testing will then be conducted on the two proposed systems to be implemented. The test will measure battery life, charge time, weight, temperature, noise levels, current flow, voltage drop and power dissipated. The following is a detailed account of the testing to be performed.
Test Setup
Each test will be conducted with the same setup in the same conditions in order to avoid any inconsistencies in testing. Each power source will be connected in parallel with a load tester, and each measuring device will be set up to document its specific metric. Each test will be set up to measure the current immediately leaving the battery, and the voltage drop across a load tester, which simulates the power that would be drawn from the battery during normal use. Thermocouples will be set up to measure the temperature of the power source as well as the ambient temperature of the room. In Figure 37, a schematic of the test setup is shown.
82
Figure 37 - Test Setup Diagram
Equipment
In order to accurately simulate the load placed on the power supply during use of the TALON robot a load tester will be used. The load tester has to simulate both a 250 watt load and a 750 watt load due to the nature of the electrical systems onboard the TALON. To fulfill these capabilities the GL1000 Electronic DC Load Tester by SBS Battery was selected, which can be seen below in Figure 38. The load tester can handle up to 27.7 amps at 36 volts and provide up to 1000 watts of power dissipation, which is more than enough for the testing conditions.
Figure 38 - SBS GL1000 Load Tester
83 In order to accurately measure the required metrics during the test, National Insturments LabVIEW software and accompanying hardware will be used. LabVIEW is a data acquisition system that uses simple, visual computer programming for data monitoring and records. The standard LabVIEW will be used to collect data from thermocouples placed in the necessary sections of the circuit, which will then be fed into the LabVIEW program to monitor the required metrics. A visual representation of the LabVIEW program used can be found in Figure 39.
Figure 39 - Sample of LabVIEW program
This program constantly tracks the temperatures, voltages and currents that will be needed for analysis after the test. It also logs and graphs these values for visual representation throughout. The physical setup for the test will be a simple circuit setup as Figure 39 represents, however Figure 40 shows the equipment and how it will be arranged in the test bed. The equipment that will be used is a power source, in this case a generator, the voltage adapter, the load tester and the computer equipment required to monitor data inputs from LabVIEW. The test setup will be the same for the any battery chemistries that are tested, with the generator replaced by the appropriate battery.
84
Figure 40 - Test bed Procedure
Baseline Testing
1) Fully charge a lithium ion battery. Battery should sit for at least four hours. 2) Weigh lithium ion battery 3) Record room temperature 4) Attach fully charged lithium ion battery to load tester. 5) Set load to 250W. 6) Activate load. 7) Record noise levels, voltage of the battery and current flow and temperature radiating from battery surface for duration of test. 8) Drain battery to minimum voltage. 9) Record time to drain battery. 10) Recharge the battery. 11) Record time to fully charge battery. 12) Repeat steps 3 – 10 five times for the same battery. 13) Repeat steps 1 – 12 with the load set to 500W. 14) Repeat steps 1 – 13 for lead acid battery.
Lithium Ion Phosphate Battery Testing
1) Fully charge a lithium sulfur battery. Battery should sit for at least four hours. 2) Weigh battery. 3) Record room temperature. 4) Attach fully charged lithium ion battery to load tester. 5) Set load to 250W. 6) Activate load. 7) Record noise levels, voltage of the battery and current flow and temperature radiating from battery surface for duration of test.
85 8) Drain battery to minimum voltage. 9) Record time to drain battery. 10) Recharge the battery. 11) Record time to fully charge battery. 12) Repeat steps 3 – 10 five times for the same battery. 13) Repeat steps 1 – 12 with the load set to 750W.
Gas Powered Generator Testing
1) Fully charge a lithium ion battery. Battery should sit for at least four hours. 2) Fill gas tank of power generator 3) Weigh total system. 4) Record room temperature. 5) Attach fully charged lithium ion battery to load tester. 6) Attach generator to lithium ion battery. 7) Set load to 250W. 8) Activate load. 9) Record noise levels, voltage of the battery and current flow and temperature radiating from generator surface for duration of test. 10) Drain battery to minimum voltage. 11) Record time to empty generator gas tank. 12) Record time to drain battery. 13) Recharge the battery. 14) Record time to fully charge battery. 15) Repeat steps 3 – 10 five times for the same battery. 16) Repeat steps 1 – 12 with the load set to 750W.
86 APPENDIX B
DEFINITION OF TERMS
Memory – effect on a battery where, when not fully discharged after each use before recharging, the unused portion of the battery will crystallize and become unusable over time.
Deep Cycling – the act of fully discharging a battery before recharging.
Energy Density – A characteristic of a power source given as watt-hours per unit weight or watt-hours per unit volume.
87