ECE 477 Digital Systems Senior Design Project Rev 8/09 s1

ECE 477 Digital Systems Senior Design Project Rev 8/09

Homework 3: Design Constraint Analysis and Component Selection Rationale

Team Code Name: Hoard Robotics Group No. 2 Team Member Completing This Homework: Trenton Andres E-mail Address of Team Member: [email protected]

NOTE: This is the first in a series of four “professional component” homework assignments, each of which is to be completed by one team member. The body of the report should be 3-5 pages, not including this cover page, references, attachments or appendices.

Evaluation:

SCORE DESCRIPTION Excellent – among the best papers submitted for this assignment. Very few 10 corrections needed for version submitted in Final Report. Very good – all requirements aptly met. Minor additions/corrections needed for 9 version submitted in Final Report. Good – all requirements considered and addressed. Several noteworthy 8 additions/corrections needed for version submitted in Final Report. Average – all requirements basically met, but some revisions in content should 7 be made for the version submitted in the Final Report. Marginal – all requirements met at a nominal level. Significant revisions in 6 content should be made for the version submitted in the Final Report. Below the passing threshold – major revisions required to meet report * requirements at a nominal level. Revise and resubmit. * Resubmissions are due within one week of the date of return, and will be awarded a score of “6” provided all report requirements have been met at a nominal level. Comments: Score - 7/10 (AP)

1. The report can be improved further. Writing skills are OK. 2. My major concern is regarding the navigation aspect. Your design doesn’t provide you any information for dead-reckoning (using wheel encoders, inertial sensors, etc). How do you plan to co-ordinate with other robots when you don’t really know your own position or is it more of just random search by all robots together? 3. Further you mention “simulated chemical spills” which is a bit ambiguous. Clearly state how you plan to implement that e.g. light source and ambient light sensors on robots 4. The pin count is a bit erroneous. Power constraint section needs to done with V-I constraints. Component selection rationale though realistic doesn’t really give details of parameters like programming interfaces, operation frequency, etc. 5. It seems you are still left with a lot of component selection. I would recommend to speed things up a little. ECE 477 Digital Systems Senior Design Project Rev 8/09

1.0 Introduction The Hoard Robotics project aims to design and build a group of eight identical wheeled robots. Each robot will be simple, inexpensive, and of limited capability. However by working together as a “swarm” the robots will be capable of accomplish complex and difficult tasks. Each robot will have the capability to gather data about its surrounds and communicate with other members of the swarm through a wireless network. It will also navigate through its environment according to a set of simple behavioral algorithms. The objectives of this project place a number of constraints on the design of the individual robots. In addition to the general constraints of size and power consumption associated with any mobile robotics project, we have had to deal with the issues of constructing eight identical robots. 1.1 Project Specific Success Criteria 1) An ability for each agent to avoid obstacles autonomously 2) An ability to detect direction and proximity of other objects to agent using IR sensors. 3) An ability to transmit data packets among agents using an ad-hoc RF network. 4) An ability to utilize swarm behavior to find a simulated chemical spill. 5) An ability to utilize swarm behavior to avoid a predator. 2.0 Design Constraint Analysis There are many constraints that must be applied to select which component to use in a design. We will consider many different requirements for each component. There are two major constraints that we must keep in mind during component selection: cost and fabrication complexity. Cost will be very important for all the components in our design. When comparing two similar products we must keep in mind that a difference in a few dollars will be magnified by the number of robots and the need for spares. While each robot will not be expensive on its own, our success hinges on multiple copies working together. Cost will often come into direct conflict with our second major design constraint: complexity. During the final phase of the project we will have to construct and test eight copies of our robot design. This requires that the component selections we choose should minimize the amount of fabrication and troubleshooting necessary during the construction phase of the project. Keeping this in mind we should attempt to choose a balance between the cost of a component, and how difficult it will be to integrate and test the final design.

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2.1 Computation Requirements Computation and control will be handled purely onboard each robot. No central controller or computer will be coordinating the actions of the swarm during a game or task. Therefore During normal operations each robot’s microcontroller will have to: poll IR and ambient light sensors, handle network communication, control left and right motors, and integrate data from sensors and information from other members of the swarm to make decisions about behavior. Many of these tasks require real-time attention. For example to avoid collisions the microcontroller will have to sample, analyze, and decide in a fast enough loop to take appropriate action.

2.2 Interface Requirements The microcontroller must have enough general purpose I/O pins to interact with the other components. Two pins will be required for indication LEDs and an additional pin will be used to control the six IR emitter LEDs. All three pins will drive LEDs indirectly through optical isolation or a MOSFET. We will also need two GPI/O pins for H-bridge direction control. The wireless module will require two GP I/O pins in addition to the SPI interface. In addition we will use two GPI/O pins connected to a DIP switch for debugging purposes. Our pin requirements are laid out in table 2.2.1 below.

Connection Number of Pins Notes Indication LEDs 2 Optically Isolated IR LEDS 1 Drives MOSFET H-Bridges 2 Wireless Module 2 DIP Switches 2 Table 2.2.1 GPI/O Pins

2.3 On-Chip Peripheral Requirements The wireless module will require a single four wire SPI interface in addition to the GPI/O pins mentioned above. We will have six IR and two ambient light photodiodes, all of which will require an A/D channel for a total of 8 A/D channels required. We will also need two single bit PWM channels for motor control. Our on-chip requirements are outlined below in table 2.3.1.

Connection Peripheral Type Number IR Photodiodes 1-channel A/D 6 Ambient Photodiodes 1-channel A/D 2 Wireless module 4 wire SPI 1 H-Bridges PWM 2 Table 2.3.1 On-Chip Peripherals

2.4 Off-Chip Peripheral Requirements Our design will not include any off-chip peripherals.

2.5 Power Constraints Each robot will be solely powered by a battery, which necessitates care when deciding upon components. The motors will most likely be the most power-hungry components we select, with the LEDs coming in second. However we don’t anticipate much challenge with motor selection because each robot is quite small, light, and will not have to navigate anywhere except a flat surface. We will definitely need at least one power regulator for the microcontroller, and possibly another for the wireless module should they require different voltages. To simplify the design and reduce power usage, we should attempt to choose those components to run at the same voltage level.

2.6 Packaging Constraints The packaging constraints are fairly simple and straightforward. The packaging needs to serve as the structural chassis for the robot as well as protecting the internal components from impact damage. In addition the packaging should provide a level surface to give the robot’s sensors the most effective range of view, and it should not interfere with the wireless module which will be placed on top of the robot. The packaging should be as light as possible to reduce power consumption when moving. The most important constraint on the packaging will be simplicity and ease of fabrication. The chassis/packaging should also allow us to easily replace components should they fail if possible. However this is not so much a requirement as it is a feature.

2.7 Cost Constraints While there are no hard constraints (except our wallets) for the project, our purpose is to show how inexpensive and simple robots can be organized to perform a complex task. This purpose is largely defeated if the swarm based solution has a higher or equal cost to a single complex robot solution. With this in mind each component considered should be as inexpensive as possible, while still having suitable performance. 3.0 Component Selection Rationale There are three major components in the design for which it is necessary to compare choices. These three components are the motor-drive trains, the microcontroller, and the wireless module. Each one of these components is a critical part of the design and required careful consideration when choosing. Initially we were considering direct drive DC motors for our robots, however after concerns in regards to starting torque, speed control, and finding appropriate wheels we started looking at geared motors. Due to our low performance requirements and stringent cost requirements the choice came down to which plastic geared motor we should purchase. The choice is currently between Solarbotics GM3 [1] and Pololu’s #1120 [2] plastic gearmotors. Both gearmotors run at 6V, they have similar gear ratios, both have the right angle form factor that we require, and cost about the same. While almost identical products in both form and function there are two things that set them apart. The first is the difference in documentation available: Solarbotics has a wealth of documentation and specification on the GM3, while Pololu has a very restricted table and no downloadable data sheets. The second is a combo deal that Solarbotics offers [3]. We could purchase the GM3 and a matching wheel for a good price. This satisfies both major criteria of cost and final production complexity. The next major component to consider is the microcontroller, applying the design constraints from above we have narrowed it down to two possible microcontrollers. The first is Microchip’s PIC18F26J134[] and the second is Freescale’s MC9S08QE64CLC[5]. Both have suitable numbers of peripherals and pins. Choosing between the two based off of our design constraints has proven to be difficult. However three important considerations have led us to choose the PIC. Firstly we were able to order samples of our selection from microchip, second is that there is more documentation available for the PIC, and finally we were able to find a wireless solution from microchip that will work well with this microcontroller.

Our selections for a wireless solution came down largely to the two major design constraints discussed above. Our choices have come down to two choices, the first is a pre-built module: Microchip’s MRF24J40MA [6]. The second option is to build the wireless system using Microchip’s MRF49XA [6]. Both options are capable of easily integrating with the PIC microcontroller but the 49XA and the associated components to build the antenna would be substantially less expensive than the 24J40MA Module. However making a custom antenna system would add a large amount of complexity to our final design. This would make the final fabrication and testing of the robots much more difficult. While we would like to use the less expensive option, the savings are not worth the difficulty associated with building and testing 8 antenna systems.

4.0 Summary In section 1 of this document we outlined the objectives of the swarm robotics project and gave a brief overview of the design of each robot. In section 2 we analyzed the relevant constraints for component selection. Subsection 2.1 through 2.4 focused on constraints applied to microcontroller selection. In subsections 2.5 through 2.7 we analyzed the power, packaging, and cost constraints of the project. In section 3 we compared choices for the microcontroller, the wireless module, and the power train system and discussed the rationale for the final choices.

List of References

[1] Solarbotics Ltd, “Gear Motor 3 – 224:1 90 Degree Shaft - Specifications” [Online] Available: http://www.solarbotics.com/products/gm3/specs/

[2] Pololu Corporation, “200:1 Plastic Gearmotor 90-Degree Ouput” [Online] http://www.pololu.com/catalog/product/1120/specs

[3] Solarbotics Ltd, “GMPW Deal – GM2/3/8/9/17 With GMPW” [Online] Available: http://www.solarbotics.com/products/gmpw_deal/

[4] Microchip Technology Inc, “PIC18F26J13” [Online] Available: http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en548700

[5] Digi-Key Corporation, “MC9S08QE64CLC-ND” [Online] Available: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MC9S08QE64CLC- ND

[6] Microchip Technology Inc, “MRF24J40MA” [Online] Available: http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en535967

[7] Microchip Technology Inc, “MRF49XA” [Online] Available: http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en541404

IMPORTANT: Use standard IEEE format for references, and CITE ALL REFERENCES listed in the body of your report.

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Appendix A: Parts List Spreadsheet Vendor Manufacturer Part No. Description Unit Cost Qty Total Cost Microchip Microchip PIC18F26J13-I/SO 8-bit microcontroller $0.00 10 $0.00 Mouser Microchip MRF24J40MA Wireless Module 2.4GHz $9.95 10 $99.50 Solarbotics Solarbotics GM03 Geared Motor and wheel $7.98 18 $143.64 Mouser Fairchild QSE773 IR Photodiode $0.58 56 $32.48 Mouser Everlight IR908-7C IR emitter $0.15 100 $15.00 Mouser Dialight 598-8270-107F SMD Green LED $0.10 20 $2.00 Mouser Dialight 598-8210-107F SMD Red LED $0.10 20 $2.00

TOTAL $294.62

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Appendix B: Updated Block Diagram