Gizmo

Individual Report Oli Thompson Abstract Jumping is an alternative means of locomotion for small scale robots and offers various advantages over wheels or legs. The speed and efficacy of traditional robots is significantly constrained by the conditions and terrain of travel. This problem becomes more pronounced with smaller robots who are unable to manoeuvre over objects above certain radii. Jumping robots are affected less by terrain and can traverse much larger obstacles, making them ideal for use in hard to reach areas; a practical example being search and rescue. This report details the development and design of a monopod jumping robot. The engineering challenges associated with jumping robots include weight limitations, self-righting mechanisms, ingress protection, jump height and distance, less accurate control over locomotion and the difficulties of changing direction mid-jump. These are all challenges that work against each other, and each required careful consideration throughout. Following initial sketches research into boimocry of jumping animals and insects, the design process involved calculating the dynamics of the jumping system using matlab to establish the required spec- ification of the important components (e.g. motor and gearbox). Block sketches and initial CAD were iterated upon until a Solidworks 2017 assembly of the final robot was completed. This model was tested with for various failure modes and flow simulation was used to analyse the robot’s propeller and rudder mechanisms. The finished robot’s calculated jump height and distance are aproximately 1m x and 2m respectively. The housing satisfies a minimum IP54 rating and is capable of at least twenty jumps on a single charge. In addition to this the robot can right itself regardless of its landing orientation and is able to change the horizontal locomotion force using a variable pitch propeller which allows precise control over the launch trajectory. The jump speed is also variable allowing the robot to jump to different heights. The robot’s total mass is 195.29g, not including the black box containing the electronics, (the weight of which was not given) and the total cost of the robot came to £82.81; this figure includes the retail price of all standard and purchased components, and the prices of the various raw materials used. Manufacturing costs were not included as the manufacturing volume was not specified; a single prototype would have considerably higher initial costs wheras were it mass produced the cost figure would be more accurate. The blackbox was also not included in this figure as this report details the the mechanical aspects of design, and not the elctronics or control systems. Contents Abstract 2 Abbreviations & Nomenclature 3 Introduction 3 Research 3 Calculations 5 Bought Components 6 Morphological Analysis 7 Initial Sketches 7 Manufacture 7 Iterative Design 8 Mechanisms 9 Key Components 13 Flow Simulation 15 Conclusion 16 References 17 2 Abbreviations & Nomenclature CoM – Centre of mass I - Current LiPo – Lithium Polymer V - Voltage FEA - Finite Element Analysis a - Acceleration

m – Mass NA – Number of turns IP – Ingress Protection h – Hours ABS - Acrylonitrile Butadiene Styrene µ - Coefficient of friction

CD – Coefficient of Drag G – Shear Modulus t – Time k - Spring rate J - Joules S - Displacement g – Gravitational force at sea level ω - Angular Velocity ρ – Density n - Factor of Safety

E – Energy Ct - Shock Fatigue Factor, Torques Fy – Force acting vertically Cm - Shock Fatigue Factor, Moments Fx – Force acting horizontally Sy - Tensile Yield Strength Fair – Opposing Force from air resistance T - Shaft Torque P – Power M - Applied Bending Moment

v – Velocity Ft - Tangential Component of Tooth Force r – Radius Kv - Velocity Factor d – Wire Diameter V- Pitch Line Velocity

D - Diameter ba - Face Width v0 – Initial Velocity Y - Lewis Number rpm – Revolutions per Minute m - Module τ – Torque σ - Bending Stress Introduction Jumping robots offer greater agility in rough terrain than typical Criteria Value robots and design inspiration can be drawn from the various Jump Height 300 mm jumping animals and insects found in nature. The monopod robot had to be designed to meet the technical metrics in table 1. The Jump Distance 300 mm electronics and control aspects of this robot will not be detailed Cost < £100 in this report and are represented by a black box of dimensions Mass < 200g 10mm x 20mm x 45mm which was housed within the robot in accordance with the ingress protection criteria. An optional Ingress Protection IP54 challenge was to control the angles of trajectory and yaw during Table 1 the jump. Research Biomimicry proves particularly useful when designing linkages that transfer the largest force from the muscle (or spring) to the ground with maximum efficiency. It is equally important that the thrust force acts over a short period of time otherwise the leg will have reached full extension before the force reaches its maximum. Both animals and insects can exhibit impressive jumping abilities. The biology of animals is considerably more complex than that of insects; when looking at leg joints animals typically have more degrees of freedom allowing greater articulation and asymmetric movement over their two hind legs. When adapting a bipedal jumping mechanism into a single foot this complexity of motion introduces several unknowns. Muscle contraction is the typical source of energy in a jumping mammal, with elastic mechanisms (usually tendons) saving 20% - 30% of the metabolic energy required for saltation. Insects rely predominantly on the elasticity of a cuticle made from resillin, a material that demonstrates near perfect elasticity with 97% of the stored energy being released as mechanical energy. As a result, the jumping mechanism for an insect is more analogous to a sprung linkage operating in a single plane than that of a mammal and as such insects rather than mammals were chosen as a basis for research. The flea is able to attain the highest jump height of any insect in relation to its size, followed by the froghopper and grasshopper. When borrowing effective design from nature it is necessary to consider the effects of scale; most insects have a much smaller surface area to volume ratio than robots of this size, and it is not guaranteed that the mathematics of motion will still give the desired results because of the square cube law. With this in mind the jumping mechanism of the grasshopper was chosen for further research and development as they are typically 30 and 20 times larger than the flea and froghopper respectively (grasshoppers typically measure 50mm in length), 2 even if the relative jump height is less. 3 During a jump a grasshopper stores around 50% of the energy in the femur-tibia joint, with the remainder stored in the extensor tendon and the cuticle of the femur (Figure 1). The grasshopper begins by inducing flexion in the femur tibia joint, and angling the coxa femur joint to control launch elevation. It is worth noting that the grasshopper can release the sprung joint regardless of how much energy is stored; allowing precise control over launch velocity. The tibia tarsus joint Figure 1 - Grasshopper hind leg plays no role in the jumping mechanism and serves to improve traction with the ground during the jump. The coxa-femur, femur-tibia and tibia tarsus joints all have a single degree of freedom and are as such well suited to a two dimensional linkage system. The experimental data shown in Table 2, along with the plot of angular position against time (Figure 2) can be used to design a linkage mechanism as close as possible to that of the grasshopper. The dimensions were scaled up and equation driven Solidworks sketches were used as a basis for the iterative design process of the linkage (Figure 3), as a precursor to 3D modelling. By examining the angles between tibia and femur it became apparent that the linkage had to move Figure 2 - Joint angles throughout jump - http://citeseerx.ist.psu.edu/ symmetrically, with the thorax - knee joint viewdoc/download?doi=10.1.1.98.4074&rep=rep1&type=pdf distance roughly equal to the tarsus knee Total body mass (M) 415 mg joint distance at all times during the jump. This critical geometry enables the linkage Tibia length 15.6 mm to maintain a linear direction of force Femur length 17.1mm which is essential for maximum efficiency. Body Linkage Design Structure Femur max - min diameter 3.2 - 0.8 mm Firstly consideration was given to the Tibia tubular diameter 0.6 mm linkage design as the calculations overleaf rely on the linkage geometry. A Angle of rotation of tibia 165 ° grasshopper is able to control 3 joints to Horizontal distance 302 mm ensure linearity, but to use this method in Jumping a robot would require 3 extra actuators. Performance Take-off angle 33.8 ° Instead a parallel linkage can be used Potential Energy 20 µJ to keep the chassis in line with the ground, but this method fails to control the Table 2 - http://citeseerx.ist.psu.edu/viewdoc/download?- geometric symmetry. This was solved with doi=10.1.1.98.4074&rep=rep1&type=pdf the final linkage iteration which utilised segments at a 1:1 ratio attached to opposite linkages to ensure even expansion and contraction of the leg (Figure 4). These included hollow sections in order to reduce weight.

Figure 3 - Grasshopper Linkage sketch Figure 4 - Geared linkage 4 The grasshopper relies on the grip in its tarsus to push itself into a forward launch trajectory rather than a vertical one, by contrast the robot only relies on the propeller for its forwards motion and only requires the linkage to gain height. A grasshopper’s launch angle is variable, but achieves maximum distance at 33.8° ±10.2°; degrees, this means that the mechanism must be rotated through this Reinforcing Boss same angle to give the maximum vertical launch velocity. It is Body Fixings also important that the line of action of the jumping force acts through the centre of mass of the robot; this can be controlled by changing the location of the body-linkage fixings. Cross Bars Once the linkage shape and geometry were established the decision was made to use two identical Cutouts linkages opposite to each other connected with cross beams Torsion Spring and secured with circlips; allowing for grasshopper-accu- rate placement of the spring at the ‘knee’ joint. Loose fitting tolerances of H11 and C11 were used for the holes and shafts Geared Linkage respectively. The crossbeams holding the torsion springs have a larger diameter to withstand the increased load (see Page 15). This system accurately mimics the grasshopper’s 2 legs Circlips and offers improved stability as well as removing the necessity Curved Linkage of having a wide foot that could interfere with the self-right- ing system, which will be examined later. The self-righting Foot system also drove the design logic behind the extended curved linkage and the small area of contact between the foot and the ground. The final linkage is shown in (Figure 6) and can Figure 6 - Completed Leg be viewed in motion here. Please note the torsion spring is left unsecured to allow free movement of the CAD model. Calculations Calculations were required to choose the battery, Equations 1 motor and gearbox, whose technical metrics will be examined overleaf. The mass of the robot was Equation 2 assumed to be 200g, the upper limit of the spec- ification. The first stage was to establish a launch Equation 3 velocity, projectile motion was unnecessary as this robot jumps upwards rather than forwards, relying on Equation 4 an external propulsion method for horizontal motion. Equation 5 An iterative matlab method was used to consider Equation 6 air resistance. The maximum height was chosen as 700mm, safely above the 300mm minimum, along with an air density of 1.2kg/m3, gravitational constant Equation 7 of 9.8067 and a conservative estimate of a 50cm2 area with a drag coefficient of 1.28. The result was a vertical launch velocity of 5m/s With the launch speed established equation 8 was used to determine the energy required to launch the robot. The arrived value was 6.4J. 5J.

Equation 8

The force required to accelerate the robot was found using equation 9, using the distance of 283mm which was the displacement of the robot’s centre of mass between release and the point of leaving the ground. The robot required 22.6N of force to do this.

Equation 9

22.6N was the average value of force the torsion springs must exert to accelerate the robot to the correct speed, in order for the torsion spring’s force to average 22.6N the force given by the spring at maximum displacement must be equal to double this value, giving 45.2N as the spring’s maximum force. 2 springs will be used in parallel due to limitations in size. Using the geometry of the linkage it can be calculated that the spring will move through 117.11 degrees, (2.0439 radians).The spring rate can now be calculated by equating the kinetic energy to the energy stored in a torsion spring 4 (equation 11) To give a spring rate of 1.197 Nm/rev. 5 Equation 10

The geometry of the spring is given by equation 11. The shear modulus of music wire is 97.2 GPa. This allows the wire diameter to be minimised to reduce weight. By changing the values iteratively, the final spring was designed to have a 2mm wire diameter, 8mm mandrel diameter and 3 turns.

Equation 11

Torsion springs reduce in diameter when under tension, which is why a 2mm clearance gap has been accounted for between the spring and the mandrel.

Equation 12

The force required to contract the leg fully will be equal to the force exerted by the spring at maximum deflection: This is the force that needs to be overcome by the motor for the robot to prime. The winch has an average diameter of 7mm, (assuming the cable to have a diameter of 2mm and that it is unlikely to wind evenly) this means that the winch shaft requires a torque of 3.164Nm by equation 12. The mhosen motor can provide a maximum 40 mNm of torque without a gearbox, and by comparing these values it was determined that a 1:80 gear reduction was required, which allowed for some manufacturing discrepancies. Motor speed is also an important factor as gearing a motor down heavily will increase the winding time. The nominal speed of the selected motor is 3450rpm which will result in a 43.125rpm output speed after gear reduction, with approximately 29 winds required to fully prime the robot, the wind time will be around 21 seconds. It should be noted that whilst a faster wind time would have been desirable this would have been achieved at the expense of limiting the robot’s jumping distance. Bought Components Once the technical metrics had been established through calculations the bought components were sourced. The extensive further design logic behind some of these choices, is examined in the mechanims section (page 8) but the two key metrics across all the components are cost and weight. The DC CW 4322 016+ motor (Figure) is available from Figure 7 - DC Motor Alibaba for an RRP of £40.99, the manu- facturers specification of which is shown in table 3. The motor already fits the IP54 requirements and as such needs no further protection but does however take up a considerable proportion of the robot’s final weight; 60.2g out of the 200g limit. Table 3 This was kept in mind during the design process and several methods have been Figure 8 - LiPo Battery employed to limit weight. The Dynamite DYNB0002 11.1V 200mAh 3S 20C LiPo (Figure) battery weighs 9.1g and has a volume of 34.9mm x 21.1mm x 13.1mm making it the ideal size and weight to fit inside the housing. The battery uses a losi micro connector and would have to be removed from the housing to be charged as external ports would affect the ingress protection rating. The battery can provide a continuous current of 4A which is over and above the necessary requirements and retails on eBay for £15.60. Hobby servo motors weigh 9g and are available from Hobby King at Figure 9 - Sealed Bearing £2.39. They afford 180° degrees of motion at a maximum of 0.157Nm, with an ample wire length of 25cm (Figure 10). A CAD model was retrieved from the manufacturer for use in the final assembly. Sealed plastic ball bearings were sourced from IGUS (Figure 9); the bearings have vastly improved weight characteristics with the 10mm and 4mm bearings weighing 2 and 6 grams respectively. The XirodurTM material is extremely low density and te bearings are rated to a maximum speed of 6000rpm which uits the robot’s requirements. The seal on the front of Figure 10- Servo Motor the bearing is able to keep dust away from the moving parts, and is also corrosion resistant. 6 Morphological Analysis Morphological analysis is a design method use to consider all the different solutions to a multi faceted problem. Detailed in Table 4 are various mechanisms, components and ideas that could be used to fulfill the different aspects of the criteria. The ideas that were chosen to be developed were the Torsion Spring, Harmonic Drive, Propellers, Rudder, Static O-ring, Passive Correction and LiPo Battery. The design logic behind these decisions will be examined later on. Launch Angle Ingress Propulsion Yaw Control Self Righting Power Control Protection

Passive Lithium Ion/ Torsion Spring Helical Gear box Worm gear Propellers Static O-ring Correction polymer

Compression Planetary Gear- CoM Rolling Gyroscope PTFE seals Nickel zinc Spring box manipulation Geometry

Inertial Coun- Folding Tension Spring Spur Gearbox Propellers Diaphragm Seal Nickel Hydride ter Mass Mechanisms

Constant Spherical Alkaline Worm Gearbox Gyroscope Rudder Adhesive Force Spring Housing Battery

Diaphragm Inertial Counter Active Nickel Cycloidal Drive Silicon Sealant Spring Mass Correction Cadmium

Flexible Harmonic Drive Potting Compound Flow Battery Membrane Table 4 Initial Sketches

Figure 11- Initial Sketches Manufacture Most of the parts used to make the robot will not be available off the shelf, and as such would require machining. The plastic parts that would be subject to high stresses would be made from injection moulded ABS, which can produce high tolerance and details. Despite it costing twice as much as some other thermoplastics for example polystyrene, ABS is chosen due to its excellent toughness and impact resistance, qualities that can be enhanced further by introducing glass fibre into the mixture if necessary. ABS is also suited to 3D printing, a process that can be used to minimise the density of the part by reducing the percentage infill while still maintaining excellent strength characteristics when compared to another 3D printing filament such as PLA. This advantage is important when designing parts for minimum weight. Injection moulding would be used in cases where high accuracy and tolerances were required such as gears and shafts, whereas 3D printing would suffice for the less important parts, for example the housing. Any spring components would be made of music wire and would be cold wound as the diameter is less than 18mm. Music wire has an improved Density (7860 kg/m3) and shear modulus (97.2 GPa) when compared to stainless steel (7920 kg/m3) and (69 GPa) and is better suited for this 6 application. 7 Iterative Design

The Iterative design process started Black Box Battery Motor with initial block sketches of Linkage Gearbox different mechanisms and key Black Box components (Figures 12 and Wing Flaps 13). Initial ideas used a longer Battery Clutch Winch Trigger body profile whose front and back would overhang Gearbox the linkage but this required Figure 12 - 2D Block Design 1 a more complicated gear Winch train and was later replaced Torsion Springs Linkage with a design that reorientated the motor parallel to the linkages. The motor is the Servo Motor Foot heaviest component and its placement is Servo Clutch Angle Spindle therefore critical in controlling the centre of

mass of the robot, which must be above Bearing

Trigger Winch the linkage-body joint as otherwise the Trigger Winch self-righting mechanism would not work Propeller Hub Wing Flaps and the robot may topple over when Gearbox priming itself. The centre of mass is Gearbox

Motor Motor difficult to establish with 2D sketches Figure 14- 3D Block and is limiting when positioning Design parts over one another; once the mechanisms were chosen the components were block-modelled in Solidworks to allow for easy Figure 13 - 2D Block Design 2 rearrangement (Figure 14). Variable Pitch Mechanism Servo Mass evaluation was used

Trigger Mechanism to determine the centre of mass Clutch accurately. The final iteration was Black Box modelled in much greater detail and included all the internal mechanisms key to the robot’s functioning Battery Propeller Hub (Figure 15). Please note that certain Free Wheel mechanisms and parts, for example Winch yaw control, housing linkages and propeller have been left out at this stage. The mechanisms that can

Motor be seen here will be explained and justified in detail in the next section. Gearbox Figure 15- Detailed Mechanism Design Mechanisms Transmission Wave Generator Pin Outer Gear Ring (Housing) Motor A harmonic drive was chosen to achieve (Inteference Fit) the steep 1:80 gear ratio as planetary or trains would use too many gears Wave Generator and be too heavy. This transmission uses Air Intake a toothed flexible spline that is oscillated Exposed by a wave generator (Figure 16); the spline Left Housing Half teeth mesh with an outer ring that is built into the housing. One rotation of the wave generator will translate the flexible spline by Flexible Spline Collar one tooth (equation 13), giving huge gear reductions with only 2 gears. The flexible Output Spur Gear spline is made from butyl rubber and is secured to a collar by 4 M2 screws which in turn drives the output gear attached via Motor Output Pin Flexible Spline (Transparent) (Inteference Fit) a keyway (Figure 17). The harmonic drive Wave Generator Wheels takes up minimal space and weight, can be driven both forwards and backwards Figure 16- Annotated Transmission and is capable of handling high torque Equation 13 (3.164 Nm). The flexible spline has 80 teeth 8 around its circumference and the Keyway Slot outer spline gear has 79 to give a reduction ratio of 1:80 by equation 13. Greater numbers of smaller teeth would introduce the risk of

failure under high torque, which is Keyway M2 Screws why butyl rubber was used due to its high resistance to wear. Figure 17- Assembly View of Transmission The wave generator is attached by an inteference fits with an H7 tolerance to match the tolerance of the motor shaft. The flexible nature of the spline cannot be modelled in Solidworks but an animation of the transmission can be viewed here: https://youtu.be/B8yaztuZu9c Trigger A disadvantage associated with helical gears is that the nature of the pitch angle introduces an axial force (thrust) (Figure 18) when two gears mesh. The trigger mechanism uses this axial force to translate a sliding helical gear forwards or backwards along its axis depending on the direction the gear is driven, allowing this axis to either engage or disengage with the winch through the use of a clutch mechanism. The driven gear has a larger face width to ensure that it is constantly in contact with the compound driving gear regardless of whether it is in the engaged or disengaged position Figure 18 - Axial Forces on a (Figure 19), and both gears have a pitch angle of 45 °. The pitch rotating helical gear train angle of a helical gear is usually limited to 30 ° as greater angles introduce larger axial thrust but in this case it is Sliding Gear and Axle Positive Key Slot Radial Snap Fit a desirable characteristic and as such has been enhanced. The winch is released immediately when the motor is driven backwards as the torque induced by the cable on the winch creates a force that pushes the helical sliding gear into its disen- gagement position (this force prevents the sliding gear from rotating rather than translating during the trigger process). This release cannot happen prematurely as to do so would mean the winch would either wind itself up with no energy applied Compound Spur - Helical Driven Gear Lose Fitting Hole to the system (the helical gear would rotate against Figure 19 - Trigger Mechanism engaged (left) and the winch slightly as the teeth slide over the teeth disengaged (right) of the driving gear), or the transmission would be forced to slip backwards, which is also impossible as the input and output of a harmonic drive cannot be reversed. Given that the motor only has to reverse briefly, the robot can be released at any point during the wind cycle allowing it to jump to various different heights. A micro switch would be installed into the knee joint to tell the robot when maximum contraction had been reached in order to prevent it overwinding. An apparent problem is that the gear may simply rotate freely in its disengaged position rather than translate into the engaged position; the yaw control mechanim that is connected to the transmission when the winch is disengaged prevents this from happening, by introducing the friction from the auxilliary mechanism: This means that Negative Key slot Positive Key slot it will be easier for the helical gear to translate rather than rotate. This mechanism is not included in Figure 19 or 20 as it will be examined in detail n page 11 along with its aforementioned effects on the trigger mechanism. The compound drive gear consists of a spur Winch gear and helical gear attached together that rotate at the same rate allowing the spur gear to be driven by

the transmission and the helical gear to transfer the Shoulders motion to the sliding gear. This is free to rotate on its axle which serves only to keep the gear in position Figure 20 - Exploded View of Trigger and Clutch relative to the housing through two shoulders (Figure 20). The sliding gear is constrained by a loose fitting hole in the housing and a radial snap fitting (Figure 19), without which the two parts would be impossible to assemble as the sliding helical gear and its axle are a single part. The clutch mechanism uses a positive key shape that slides into the negative key shape on the winch axially (Figure 20), its rounded edges minimising the risk of jamming. If the key did not 8 engage immediately then the helical gear would simply rotate whilst semi engaged and realign 9 itself after a quarter turn, whereupon the axial force from the helical gear would push the sliding gear into the fully engaged position. The gears shown in Figure 20 are complex parts that cannot be purchased off the shelf. The sliding gear and its axle are a single part, the same being true for the copound gear. Due to their complex geometries these parts may require some post processing after the injection moulding process. Ratchet Pawls Ratchet Spring The freewheel mechanism disengages the output axle from the input axle when the output axle rotates faster than the input axle. It is used in bicycles to prevent the rotation of the rear wheel from turning the pedals and can be used to similar effect here to allow the propeller to continue spinning after the winch spindle has stopped. The Figure 22 -Freewheel Mechanism freewheel housing is built into the winch and with transparent winch contains an array of ratchet teeth around its Axle Output Gear inner circumference (Figure 22), the angle of which is kept to a minimum Figure 21 - Freewheel to maximise efficiency in order to keep the propeller spinning for as long Mechanism as possible. The output gear supports three ratchet pawls on small axles arranged around its centre, positioned to engage the ratchet teeth when rotated in one direction and disengage when rotated in the other. The ratchet pawls are pushed outwards by a ratchet spring (Figure 21) which uses the material’s natural resistance to deflection to apply a very small outwards radial force to the ratchet pawls. The geometry of the spring is designed to minimise its outwards force, as extra force would introduce friction into the mechanism which would actively slow the propeller down. The winch has been designed to centre itself on the central axle of the output gear, ensuring correct alignment, and contact with the ratchet pawls. Glass fibre reinforced ABS would be used to withstand the high bending moment and the shaft would be kept as short as possible. The bending moment was calculated using the shaft length and spring force, which allowed the diameter of the shaft to be found using equation 14 using a factor of safety of 2, standard values for Ct and Cm and the appropriate torque and tensile yield strength. A solid shaft f 6mm ø was found to be able to withstand the forces. Equation 14 Cable & Winch The cable is secured to the winch through two 2mm ø holes with a small knot. The winch spindle is designed to be as narrow as possible to increase the unwinding speed, without the spring force causing it to fail. The cable itself is made of 2 mm ø waxed nylon cord, which uses a high performance nylon weave to produce excellent tensile strength characteristics at small radii. The waxed coating reduces Winch Cable friction between different layers of string, and reduces the likelhood of entanglement, as well as having the added advantage of preventing water from soaking into the string and up into the housing. The cable passes through a small hole in the housing and is secured to the rear cross bar in the foot. The cable has not been modelled in Solidworks Figure 27 - Winch Cable but care was taken to allow ample room for it to move, considering the winch will not wind up evenly each time. Variable Pitch Propeller The rotation of the propeller is not controlled by an independent actuator which means its speed and direction of rotation cannot be changed in the typical manner. Instead the robot relies on a small servo motor to dynamically alter the pitch of the propeller blades throughout the jump, allowing complete control of the forwards thrust force from the moment the robot leaves the ground. Changing the pitch of the propeller has Figure 23 - Back and Front Views Of Variable Pitch a similar effect to a car’s gearbox, with a large propeller Mechanisms angle representing a high gear and a small angle the low gear, meaning the robot can dynamically alter the force the propeller exerts as it moves at different speeds, whilst mainting a constant angular velocity. This has the advantage of allowing the robot to change its trajectory rather than launching with a set trajectory, so for example the robot could jump upwards a certain distance before moving forwards, allowing greater control over the jump path. 10 The propeller rotates around a ball bearing to reduce friction (Figure 24), the centre of which allows a pitch control rod to pass along the propeller’s axis of rotation and into the robot’s housing. When the pitch control rod is moved back and forth the captive pitch control levers inside the propeller hub are rotated and cause the propeller blades to change their pitch. The pitch control rod is pushed forwards and backwards by a cam that is driven by a servo motor and houses a small spring that applies a small force to the pitch control rod in order to keep it in contact with the cam at all times. The propeller hub itself passes through the bearing and screws into its drive gear allowing the propeller to be driven by the freewheel mechanism whilst not interfering with the pitch control mechanisms. An animation of the mechanism working can be viewed here: https://youtu.be/ dRrr6HDzasQ The servo is mounted into the left housing half with two M2 screws (Figure 32), with a third screw securing the servo cam into the servo’s output (Figure 24). The servo cam remains at a tangent to the curved edge of the pitch control rod which is kept under forwards tension by a spring that fits over the rod. The retaining collar gives the spring a surface on which its force can act and is secured in place by a set screw allowing for easy assembly. The pitch control rod houses a keyed slot that locks into the keyway that forms part of the propeller hub. This ensures that it rotates with the propeller at all times, allowing the captive pitch lever plates to be in permanent alignment with the captive pitch control levers. The levers themselves have a keyed cut-out that fits around the threaded and keyed mounting cylinder on the end of each blade, ensuring that the lever rotates with the blade (Figure 24). These two components are attached together with an M3 x 10mm screw which can be tightened with a screwdriver through the holes that have been cut into the propeller hub for this purpose. The propeller hub screws into the threaded drive gear either side of the ball bearing, trapping the assembly in place. A left hand thread is used here as the components will be constantly spinning and this could cause the threaded components to unscrew, a left hand thread reverses the unscrewing motion so the propeller’s rotation serves to tighten the components together. The proprellers themselves were created by copying aerofoil profiles of different cross sections of existing propellers and lofting the profiles together to form a complete shape. The propeller rotates directly next to the cooling intake of of the IP54 rated motor, and will increase airflow and motor performance. Threaded and Keyed Blade Propeller Blade Mounting M2 x 7mm Screw Cylinder Assembly Access Holes Set Screw for Screwdriver Servo Cam Locating Hole Left Hand Threaded Keyed Slot Drive Gear Keyed, Captive Retaining Collar Pitch Control Keyed Slot Levers

Pitch Control Rod Spring

Captive XirodurTM Sealed plastic Set Screw Lever Plates Propeller Hub Ball Bearing

Left Hand Threaded Boss Propeller Blades Servo M3 x 10mm Screw

Figure 24 - Exploded View of Variable Pitch Propeller Mechanism Yaw Control Elastic Chord An advantage of using a propeller for propulsion is that the Snap Fit Mount direction of air flow can be controlled with a rudder. This vertical Rudder fin can be angled left or right to steer the robot as it jumps Guide through the air. Typically, an external actuator would be required Holes for this extra control, but this design takes advantage of the fact that the winding motor is not in use during the jump, and Chord

after release the sliding helical gear explained in the trigger Rotating Pin section is in its disengaged position until such a time as the motor reverses its direction to begin winding again. The motor is free to turn in the ‘unwinding direction’ without affecting the helical gear’s translation and as such affords a motor output that will only turn after the robot has jumped. The disadvantage with this output is that it is one directional; if the motor were to reverse it would re-engage the 10 clutch and start winding up the leg. Nevertheless, this one-di- Figure 25 - Outer Rudder Mechanism 11 Cable M2 x 7mm Screw rectional motion can be transferred through a (Figure Crown Gear 26) to the outside of the housing, where a sprung pulley system can Rotating Pin be pulled with each revolution turning the rudder into position. If the motor continues to turn the cable will slacken and the elastic chord will pull the rudder back to the left position, this means the robot can control the position of the rudder with one direction of rotary motion. The cable and elastic chord have not been modelled in Solidworks as it would constrain the assembly. When the robot jumps the elastic chord would keep the rudder at its furthermost left position, which would cause the robot to spin if the propeller’s blades were angled so as to create thrust. Gear in Disengaged However, as soon as the robot leaves the ground, the sliding helical Position gear is already positioned to change the rudder’s angle and the Figure 26- Internal Rudder Mechanism robot can begin to turn the rudder immediately after launch. The rudder protrudes from the back of the robot introducing the possibility of breakage but the elastic chord will allow the rudder to deflect harmlessly and return to its original position should it undergo any impact. Self-Righting The robot must be able to right itself regardless of its landing orientation in order for it to continue jumping. This robot uses passive orientation correction; by manipulating the robot’s CoM and the geometry of its outer shell the robot will be able to fall back into position during the winding process. If the robot lands on its side (Figure 28) the leg will contract behind the protective propeller ring and the the robot will roll upright. When the CoM has settled the robot can relaunch.

Figure 28- Landing Scenario 1 A more likely scenario is that the robot will land on its front (Figure 29), in this case the extended curved linkages allow the robot to fold back onto its foot after the winding process

Figure 29- Landing Scenario 2 The thrust from the propeller and the high CoM reduces the likelihood of the robot landing on its rear as the foot will be the first point of contact betweeen the robot and the ground and its forwards momentum will tip the robot onto its front or side. Ingress Protection IP54 specifies limited protection against dust ingress and protection against Sealed Bearing Gasket water sprayed from any direction. Since the motor is rated IP54 by the manufacturer it is only the servo, battery, black box and some mechanisms that require protedction from dust and water. These components are mounted inside two housing halves which are screwed together with four M3 screws. The facing of the housing has a 1.6mm ø channel cut around the contact faces that houses an injection moulded 2mm ø nitrile rubber static O-ring (Figure 30). Nitrile rubber has been chosen due to its good performance with water and high resistance to tearing and abrasion. The static O-ring hugs the skf 6000 bearing and keeps it in place with an interference fit when the housing halves are screwed closed, deforming Housing (Transparent) against the components by around 20% and forming a tight seal. The Figure 30- Static O-ring bearing itself is a cover plated plastic ball bearing made from xirodur B180. and Housing Assembly The one-sided cover plate is permanently fixed to the rotating ring of the ball bearing while the opposite side is protected by an enclosed ball cage. These bearings offer excellent protection against dust ingress and are resistant against splashes of water. 12 It can be seen in Figure 31 that one half of the housing IP54 or higher Sealed Front has a 2mm ø hole through which the winch cable is wound. Section Since most of this diameter will be taken up by the cable at all times it is unlikely that water splashes would cause any serious ingress; locating the hole at the bottom of the curved inner surface of the housing means that in the event of water build up gravity would cause it to naturally drain away through the hole. Due to the potential ingress at the bearing and cable hole it is difficult to declare full waterproofing above the IP54 Static O-ring 2mm Cable IP54 Rear specification with 100% assurance: Because of this the decision Hole Section was made to bisect the housing halves into two sections, the Figure 31- Internal Rudder Mechanism first of which being IP54 specification (mostly waterproof but non-submersible), and the second section sealed completely, likely around the IP65 specification (although physical prototyping and testing is required). This front section would house the battery and electronics and would have no compromise in protection (Figure 31). The wires leading from the black box would pass into the rear section through small holes inside the housing and once the wires were in place would be sealed with potting compound. The wires from the motor and servo would also be secured with potting compound, and would be cut to length to ensure any soldered joints were inside the front section before being tinned to further minimise corrosion. For this same reason the torsion springs in the knee joint would be electrogalvanised. Housing Key Components The housing (Figure 32) has been designed to constrain all of the internal components in place, thus removing the need for a separate chassis. It also serves as a ring gear for the harmonic drive and provides ingress protection to the water sensitive components, as well as ample space for wires. A central rib is used to support various axles and bearings as well as to improve the impact resistance of the housing. Due to the complex geometry of the part the only suitable manufacturing technique would be 3D printing; ABS would be used as filament due to its relatively high yield strength. The areas of this part that would not be subject to high stresses could be printed with a lower density infill in order to reduce weight and printing time, however the key areas are modelled as solids for the purposes of FEA. The holes and fittings require a precise free running tolerance as errors in manufacture could potentially cause axles to fit either too loosely or too tightly which would constrain their motion and prevent the robot from working properly. These features would be drilled and reamed to tolerance following the 3D printing process.

M3 Threaded Hole

Ring Support Fins Yaw Gear Mount Bearing Servo Mounting Pillars M2 Threaded Hole Support Axle Snap Fit

Wire Hole

2mm ø Static O - Ring Channel

M4 Threaded Compound Harmonic Drive Battery and Central Rib Motor Mount Fasteners Gear Mount Ring Gear Black Box Fitting Figure 32- Housing Halves The protective propeller ring is supported by the protruding fin which will be subject to high impact upon landing. This scenario was simulated with FEA to ensure that the material’s yield strength was not reached. The landing force is given by the kinetic energy of the robot at the point of impact divided by the distance taken for the robot to stop as shown in equation 15.

Equation 15

The flexible nature of the protruding arm in question allows it to deflect under impact increasing the amount of time over which the force acts and therefore decreasing the impact force. For the purposes of this test the deflection displacement was assumed to be around 10mm, a figure that would later be verified by examining the displacement plot generated by the FEA process. 12 The kinetic energy was calculated using the landing speed, which was found by using the vertical 13 displacement and earth’s gravity by equation 16. This landing force is distributed over 3 fins and as such the landing force used was 15N on a single fin. The protruding fin initially followed a circular profile (Figure 33) but the material’s yield strength was exceeded and a redesign was required. Initially a lofted feature was used to increase

Equation 16 the diameter of the circular fin nearer to the housing (Figure 34), but the forces still exceeeded the yield strength. Finally, by using an elongated lofted fin profile instead of a circular section, and increasing its width nearer to the body of the robot (where the force is at a maximum) (Figure 35) the part was able to withstand the landing forces and had an improved aerodynamic profile.

Figure 33 - Small Circular Profile Figure 34 - Larger Circular Profile Figure 35 - Fin Profile

Figure 36 - Corresponding FEA Results Protective Propeller Ring The propeller ring uses a truss structure to minimise weight while maintaining the size necessary to protect the propeller regardless of which orientation the blades are in; this reduces the mass by 40%. Cable Anchor The rudder is also supported by this component, and attaches to the Cable Guide propeller ring through two snap fittings at the top and bottom of the Rudder Snap Fit ring. Snap fittings allow the rudder to be a single part as mounting the 3.2mm ø rudder through a hole would require the pulley beam to be removable. Mounting In addition to this, snap fittings allow for easier repair should the rudder Holes Truss Structure come loose. The mounting holes have a concentric layer of material around Mounting Points them for extra strength, as they were identified as key points of failure. The holes themselves measure 3.2mm in diameter to allow an M3 screw to pass through them freely. The propeller ring is made from injection Rudder Snap Fit moulded ABS for maximum impact resistance and minimum weight, and the geometry has been designed to fascilitate easy removal from Figure 37 - Propeller Ring a mould. Some post processing would be necessary to drill out the mounting holes, the tolerance of which would not be of concern as the holes are not threaded and only serve to align the machine screws. Output Spur Gear The ouptut of the harmonic drive connects to a 40 tooth spur gear (Figure 38). The face width of the spur gear must be calculated to ensure that the stresses involved in the transmission would not cause the gears to fail. The power and pitch line velocity can be found using equation 17 and 18 respectively, before the tangential component of tooth force can be calculated by equation 19. Equation 17 Equation 18

Equation 19 Figure 38 - Spur The Lewis number graph was used in conjunction with the number of teeth and Gear pitch angle to find the Lewis Number. The velocity factor is given by equation 20 which was used along with the bending stress and module to find the face width via equation 21.

Equation 20 Equation 21 The minimum face width value was calculated as 3.2mm, 5mm was used to ensure a factor of safety. The teeth are the key points of failure, therefore material removed from the body of the gear to reduce weight should not affect this. This process was applied to all the gears in the robot. 14 Upper Knee Linkage The upper linkage at the knee joint houses a crossbar that secures the torsion springs. This crossbar is 18 mm away from the torsion springs’ mandrel, and by using the combined springs’ torque of 4.89Nm at maximum displacement it can be calculated that the crossbar must withstand 271.83N of force. This crossbar is supported at both ends which means the upper linkage will be acted by 135.9N. This scenario was tested with FEA and material was added to the part to prevent failure. (Figure 39, 40 and 41). The SN Curve was retrieved for ABS so as to test the fatigue life of the part, and it was determined that the part could withstand 1000 load cycles, or 1000 jumps.

Figure 39 - Original Design Figure 40 - Material added Figure 41 - Working Design around stress points Flow Simulation To verify the efficacy of the variable pitch propeller and the yaw control mechanisms flow simulation was conducted on the robot. By changing the angle of the propeller blades the change in velocity of the air particles can be calculated, and the resultant force acting on the propeller blades can be used to find the horizontal speed and displacement of the robot. The same process can be used to analyse the change in air particle trajectory caused by deflection of the rudder. The rpm of the propeller can be calculated by using the launch velocity of the robot, as this will be the speed at which the cable is pulled from the winch when the robot leaves the ground. By using the winch (and cable’s) 7mm radius in equation 22 the maximum angular speed of the propeller at take-off is 6820 rpm, below the 8000 rpm rating of the bearing. This figure was qualified by looking at drone motors. Equation 22 The simulation was modelled as a 6820 rpm rotating region about the propeller, with a stator wall constraint at the inside of the propeller ring. The internal components were excluded from the analysis to decrease running time and surface goals were used to determine the force acting on the surfaces of each propeller blade. Initially the scenario was tested with minimum propeller blade pitch. The trajectory plot is shown in Figure 42. It can be seen that the high velocities (red) act radially around the propeller and whilst there is some forwards air motion the resultant force was only 0.03N. This Figure is the smallest achievable horizontal force. A series of similar tests was conducted with the propeller blades set to various increasing angles, the optimum angle is somewhere between 31 ° and 39 °, as larger angles would begin to decrease thrust. The flow trajectory path for maximum thrust is shown in Figure 43. A flow trajectory animation can be viewed here: https://youtu.be/FOTe9u3U7L4

14 Figure 42 - Flow Trajectory at minimum Thrust Figure 43 - Flow Trajectory at maximum Thrust 15 The horizontal acceleration can be estimated by equation 23. By using the maximum force of 1.2N and a 0.2kg mass it can be determined that the robot will accelerate horizontally at 6 m/s2, not accounting for air resistance. Equation 23 The flight time can be found using the vertical launch velocity and the force of gravity and finding the time it takes for the speed to become zero. This value can then be doubled (equation 24).

Equation 24

The total flight time was found to be 1.02 seconds, which is the time over which the horizontal force acts. These values can be used in equation to find a horizontal dsplacement of 3.12 m. The real value will be slightly less than this as air resistance has not been taken into account for the horizontal motion, but this is still safely above the 0.3 m specification.

Equation 25

Cut plots were used to analyse the effect of the rudder’s rotation and can be seen in Figures 46, 47 and 48. The rudder will provide no turning force until sufficient horizontal velocity has been achieved which is why the rudder simulation is modelled with a relative air velocity of 3m/s, which is the horizontal speed the robot would be moving halfway through its jump (Equation 25). The velocity magnitude contours can be seen in Figure 46, 47 and 48 A larger rudder would be able to change the air trajectory with better results, but due to weight constraints this was not possible.

Figure 46- Rudder turning RIght Figure 47- Rudder Centered Figure 48 - Rudder turning Left Conclusion In conclusion the proposed design of the robot theoretically meets and in some cases exceeds all aspects of the specification. There is little to be gained from further testing without building a physical prototype Component Price which would inevitably necessitate certain design changes, but a proof of concept has definitely been established. The robot weighs 195g, this DC Motor £40.99 Figure excludes the mass of the black box which has not been given, but LiPo Battery £15.60 leaves just under 5 grams to accommodate it. Hobby Servo £2.39 The total cost of the robot is £82.81; a breakdown of which is shown in Table 5. This Figure includes the raw materials cost by mass 10mm Sealed Ball £7.58 Bearing and several off-the-shelf components (inclusive of VAT) that have been used in the robot. It does not however account for the manufacturing 4mm Ball Bearing £3.80 costs of the bespoke components, that make up the majority of the parts, M2 Screws £1.25 although most of these would be 3D printed which is a relatively cheap manufacturing technique. Some parts require more advanced manufac- M3 Screws £1.62 turing (for example gears), such as injection moulding which would have M4 Screws £1.29 significantly higher start up costs, but would be cheaper in the long run if 4mm Circlips £3.19 the robot were to be mass produced. The robot is made from 101 parts which are detailed in Table 6 overleaf along with their corresponding 39.02g ABS £0.08 masses and manufacturing technique and a general assembly drawing 19.28g Music Wire £4.50 can be found at the end of this report. 9.18g Butyl Rub- £0.16 Some improvements might include giving further consideration to the ber robot’s self-righting mechanism if it were to land on its back, as well as increasing the rigidity of the protective propeller ring and housing, which 1.1g Silicon £0.40 has been designed to withstand the landing force from jumping on a flat Total £82.81 surface and not for example jumping downhill or off a ledge. The CAD models for the bearings, screws and servo were sourced online. Table 5 16 NO. PART NUMBER Material MASS/g QTY. 30 Rolling Linkage Top Pin ABS 1.30 1 1 Housing Right Half ABS 8.98 1 31 4mm Circlip ALLOY STEEL 0.17 14 2 Housing Left Half ABS 9.73 1 32 Battery Cell BOUGHT PART 3.03 3 3 Propeller Hub ABS 0.32 1 33 Servo Cam ABS 0.68 1 4 Threaded Propeller Transmission Gear ABS 0.28 1 34 Geared Top Linkage ABS 0.48 2 5 Propeller Blade ABS 0.29 3 35 Upper Jumping Beam ABS 0.42 2 6 Pitch Control Lever ABS 0.04 3 36 Middle Linkage Brace ABS 1.33 2 7 M3 X 10mm Screw BOUGHT PART 0.78 1 37 Geared Linkage Bottom Left ABS 0.59 1 8 Pitch Control Rod ABS 0.12 1 38 Foot Linkage ABS 0.1 2 9 10mm Bearing SKF 6000 BOUGHT PART 3.15 2 39 Geared Linkage Bottom Right ABS 0.5 1 10 4mm Bearing SKF 624 BOUGHT PART 0.62 1 40 Front rolling Linkage ABS 0.89 2 11 Propeller Spring MUSIC WIRE 0.5 1 41 Knee Joint Pin Front ABS 1.33 1 12 Retaining Collar ABS 0.02 1 42 Knee Joint Pin Rear ABS 1.3 1 13 Set Screw ALLOY STEEL 0.55 1 43 Knee Joint Spacer ABS 0.13 2 14 Freewheel Ratchet Pawls ABS 0.01 3 44 Foot Front Pin ABS 1.30 1 15 Ratchet Spring MUSIC WIRE 0.05 1 45 Foot Front Spacer ABS 0.05 2 16 Propeller Transmission Ratchet Gear ABS 1.41 1 46 Foot Back Pin ABS 0.26 1 17 Freewheel Housing ABS 1.58 1 47 Torsion Spring Right MUSIC WIRE 9.64 1 18 Motor BOUGHT PART 60.2 1 48 M4 X 9mm Cap Head Screw BOUGHT PART 1.77 4 19 Harmonic Drive Wave Generator Mount ABS 0.99 1 49 M3 X 18mm Screw BOUGHT PART 1.49 3 20 Harmonic Drive Wave Generator Wheel ABS 0.68 2 50 Spring Holder Beam ABS 0.54 1 21 Wave Generator Pin ALLOY STEEL 0.52 2 51 Torsion Spring Left MUSIC WIRE 9.64 1 22 Hobby Servo BOUGHT PART 9.2 1 52 Bottom Spring Holder Beam ABS 0.58 1 23 Harmonic Drive Flexible Spline BUTYL RUBBER 9.18 1 53 Helical Clutch Rod ABS 0.31 1 24 Flexible Drive Mount ABS 0.07 1 54 Static O-ring SILICON 1.1 1 25 Hamonic Drive Output Spur Gear ABS 0.18 1 55 M2 Pan X 7mm Head Screw BOUGHT PART 0.23 6 26 Helical Spur Trigger Compound Input Gear ABS 0.31 1 56 Rudder ABS 0.93 1 27 Helical Spur Trigger Axle ABS 0.11 1 57 Crown Gear ABS 0.05 1 28 Electronics Black Box GIVEN PART ? 1 58 Yaw Drive Beam ABS 0.04 1 29 Protective Propeller Ring HIPS 2.17 1 59 Gizmo Assembly VARIOUS 195.29 1 Table 6- Bill of Materials and Weights References http://www.hfsp.org/frontier-science/frontier-science-matters/insect-jumping-ancient-question https://gizmodo.com/this-adorable-robot-can-do-parkour-way-better-than-you-1789735099 https://en.wikipedia.org/wiki/Elastic_mechanisms_in_animals http://nptel.ac.in/courses/116102012/56 http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.98.4074&rep=rep1&type=pdf https://www.researchgate.net/profile/Metin_Akkoek/publication/267836773_Design_and_ Analysis_of_Grasshopper-Like_Jumping_Leg_Mechanism_in_Biomimetic_Approach/links/54e5d- a9b0cf2cd2e028b367f/Design-and-Analysis-of-Grasshopper-Like-Jumping-Leg-Mecha- nism-in-Biomimetic-Approach.pdf?origin=publication_detail https://www.igus.co.uk/wpck/7167/xiros_B180_mit_Deckscheibe http://www.solidworks.com/sw/fluid-flow-simulation-whitepapers.htm https://hobbyking.com/en_us/radios-servos/servos/hobbyking.html?mode=list&___store=en_us https://uk.rs-online.com/web/c/automation-control-gear/electric-motors-motor-controllers-pe- ripherals/dc-motors/?sort-by=Maximum%20Output%20Torque&sort-order=desc&applied-dimen- sions=4294569924 https://khkgears.net/new/gear_knowledge/gear_technical_reference/gear_forces.html https://www.igus.co.uk/wpck/4961/ballbearing http://www.madehow.com/Volume-6/Springs.html https://www.creativemechanisms.com/blog/everything-you-need-to-know-about-abs-plastic https://www.3dhubs.com/knowledge-base/pla-vs-abs-whats-difference https://www.creativemechanisms.com/blog/everything-you-need-to-know-about-abs-plastic https://www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf https://www.mh-aerotools.de/airfoils/jp_propeller_design.htm https://www.multiplyleadership.com/3-aircraft-rudder-design-characteristics-abcs-of-aircraft- tails-airplanes-by-design/ http://www.aero.us.es/adesign/Slides/Extra/Stability/Design_Control_Surface/Chapter%20 12.%20Desig%20of%20Control%20Surfaces%20(Rudder).pdf https://www.creativemechanisms.com/ratchets http://www.skf.com/uk/products/bearings-units-housings/super-precision-bearings/principles/ design-considerations/radial-location-of-bearings/recommended-shaft-and-housing-fits/ http://www.matweb.com/search/datasheettext.aspx?matguid=f1ca910ed- b5a4464896974aa5845edee 16 https://www.engineersedge.com/gears/lewis-factor.htm 17 F F E E B B A A D D C C A3 A3 1 1 1 1 REVISION REVISION SHEET 1 OF SHEET 1 OF Injection Molding TRIMETRIC VIEW 2:1 Injection Moulded DO NOT SCALE DRAWING DO NOT SCALE DRAWING 2 2 2 2 Flexible Drive Mount Geared Top Linkage TITLE: TITLE: SCALE:1:2 SCALE:5:1 DWG NO. DWG NO. SCALE 1:1 Trimetric View

DEBURR AND BREAK SHARP EDGES DEBURR AND BREAK SHARP EDGES 5 5 ABS ABS 3 3 3 3 MATERIAL: MATERIAL: WEIGHT: WEIGHT: 1.4g 200 2.60 206.96 DATE DATE As Machined 16/ 04/18 As Machined FINISH: FINISH: SIGNATURE SIGNATURE 0.15 NAME NAME 0.15 0.1MM 0.1 mm 4 4 4 4 Q.A Q.A MFG MFG CHK'D CHK'D ANGULAR: UNLESS OTHERWISE SPECIFIED: DIMENSIONS ARE IN MILLIMETERS SURFACE FINISH: TOLERANCES: LINEAR: DRAWN DRAWN Oli Thompson ANGULAR: UNLESS OTHERWISE SPECIFIED: DIMENSIONS ARE IN MILLIMETERS SURFACE FINISH: TOLERANCES: LINEAR: APPV'D APPV'D

R0.20 8 3

5 5 5 5 A FULL DEPTH INVOLUTE 5 : 1 2.08

6 6 6 6 R23.50 R23.50 0.89

45° 45°

SCALE R21.25 R21.25 DETAIL

R13.08 0.05 0.10

6 12 - + 1.68

4.90

9 9

7 R9 7 7 7

A 22.79 22.79

5.20 5.20

71.07° R2 R3.50 R3.50 7

8 8 8 8

0 0

4 4 4

0.075 + 0.075 + R3.50 R3.50 4X TAPPED M2x1.0 - 6H THRU SOLIDWORKS Educational Product. For Instructional Use Only. SOLIDWORKS Educational Product. For Instructional Use Only. F F E E B B A A D D C C C D A B E F SOLIDWORKS Educational Product. For Instructional Use Only. 4XTAPPEDM2x1.0-6HTHRU 8 8

5.20 7 7 9

4.90

1.68 + - 12 0.10 0.05

45°

6 6 5 5

8 R0.20 R0.20 APPV'D DRAWN OliThompson LINEAR: TOLERANCES: SURFACE FINISH: DIMENSIONS AREINMILLIMETERS UNLESS OTHERWISESPECIFIED: ANGULAR: CHK'D MFG Q.A 4 4 0.1MM NAME 0.15 SIGNATURE FINISH: 16/ 04/18 As Machined DATE 2.60 WEIGHT: 1.4g MATERIAL: 3 3 ABS 5 EDGES BREAK SHARP DEBURR AND DWG NO. SCALE:5:1 TITLE: Flexible DriveMount 2 2 DO NOTSCALEDRAWING Injection Moulded TRIMETRIC VIEW2:1 SHEET 1OF REVISION 1 1 A3 C D A B E F C D A B E F SOLIDWORKS Educational Product. For Instructional Use Only.

+0.006 R6 R6

8 3 0 8 2 7 7 6

4 6 6 29 25 +

0 0.0012

R10 R10 5 5 10 2 APPV'D LINEAR: TOLERANCES: SURFACE FINISH: DIMENSIONS AREINMILLIMETERS UNLESS OTHERWISESPECIFIED: ANGULAR:NA DRAWN CHK'D MFG Q.A 4 4 OLI THOMPSON 0.1mm NAME +0.006

R6 R6 3 0 SIGNATURE FINISH: AsMachined 24/04/18 DATE WEIGHT: 0.68g MATERIAL: 3 3 ABS EDGES BREAK SHARP DEBURR AND TRIMETRIC VIEW SCALE 2:1 DWG NO. SCALE: 5:1 TITLE: Harmonic DriveWave 2 2 Generator Mount 1 DO NOTSCALEDRAWING Milled

SHEET 1OF 1.50 1.50 REVISION 1 1 A3 C D A B E F 8 7 6 5 4 3 2 1

R6 29

F 25 F

R10

0.006 0 0.006 0

+ +

E 3 3 E

TRIMETRIC VIEW

2 +0.0012 2 R6 SCALE 2:1 4 0 D D 1.50

C C

6 10 1.50

B B

UNLESS OTHERWISE SPECIFIED: FINISH: As Machined DEBURR AND DO NOT SCALE DRAWING DIMENSIONS ARE IN MILLIMETERS BREAK SHARP REVISION SURFACE FINISH: EDGES TOLERANCES: LINEAR: 0.1 mm Milled ANGULAR: NA

NAME SIGNATURE DATE TITLE:

DRAWN OLI THOMPSON 24/04/18

CHK'D Harmonic Drive Wave APPV'D Generator Mount A MFG A Q.A MATERIAL: DWG NO. 1 A3 ABS

WEIGHT: 0.68g SCALE: 5:1 SHEET 1 OF 1 8 7 6 5 4 3 2 1 SOLIDWORKS Educational Product. For Instructional Use Only. 8 7 6 5 4 3 2 1 ITEM NO. PART NUMBER QTY. 1 Wave Generator Pin 2 Harmonic Drive Wave F 2 Generator Wheel 2 F Harmonic Drive Wave 3 Generator Mount 1 4 Flexible drive collet 1 5 Motor 1 Harmonic Drive 6 Flexible Spline 1 E 7 M2 Pan X 7mm Head 4 E B Screw 3 1 2 7 9 4 6 5 8 Part1 1 Harmonic Drive 9 Output Spur Gear 1

D Trimetric View D SCALE 1 : 1

5

1 C C 2

6

SECTION B-B B B B SCALE 2 : 1

DO NOT SCALE DRAWING REVISION

TITLE: Transmission Assembly A A DWG NO. A3

SCALE: 2:1 SHEET 1 OF 6 8 7 6 5 4 3 2 1 SOLIDWORKS Educational Product. For Instructional Use Only. 8 7 6 5 4 3 2 1 ITEM NO. PART NUMBER QTY. 2 Freewheel Ratchet B 1 Pawls 3 F 1 2 Ratchet Spring 1 F ISO - Spur gear 0.7M 3 37T 20PA 5FW --- 1 S37A75H50L6.0N 4 Freewheel Housing 1

1 E E

B SECTION B-B SCALE 2 : 1

D D

C 4 C

A A Dimetric View 3 SCALE 2 : 1 1 B B 3 DO NOT SCALE DRAWING REVISION

4 TITLE: Freewheel Mecahnism 2 and Winch A A DWG NO. SECTION A-A A3

SCALE 2 : 1 SCALE: 2:1 SHEET 2 OF 6 8 7 6 5 4 3 2 1 SOLIDWORKS Educational Product. For Instructional Use Only. 8 7 6 5 4 3 2 1

A 10 7 6 8 5 F F

E E

3 A SECTION A-A SCALE 1 : 1 1 9 2 4 3 D D

ITEM NO. PART NUMBER QTY. 1 Pitch Control Rod 1 2 Pitch Control Lever 3 4 1 3 Propeller Blade 3 C C 10 9 4 Propeller Hub 1 5 Threaded Propeller 1 5 Spur Gear 6 Retaining Collar 1 1 2 7 Propeller Spring 1 8 Set Screw 1 8 9 M3 X 10mm Screw 3 4 B 10mm Bearing SKF B 10 6000 1

DO NOT SCALE DRAWING REVISION

TITLE: Variable Pitch 3 Propeller Mechanism A A DWG NO. A3

SCALE: 1:1 SHEET 3 OF 6 8 7 6 5 4 3 2 1 SOLIDWORKS Educational Product. For Instructional Use Only. 8 7 6 5 4 3 2 1 ITEM NO. PART NUMBER QTY. 1 Wave Generator Pin 2 Harmonic Drive Wave F 2 Generator Wheel 2 Adhesive Pad 15 F Harmonic Drive Wave 3 Generator Mount 1 Adhesive Pad 4 Flexible drive collet 1 Harmonic Drive 5 Output Spur Gear 1 6 Motor 1 E 7 Harmonic Drive 1 E Flexible Spline 14 8 Housing Left Half 1 M2 Pan X 7mm Head 9 Screw 7 5 10 Hobby Servo 1 12 11 Servo Cam 1 4 Helical Spur Trigger 12 Compound Input 1 13 D Gear 7 D 13 Helical Spur Trigger 1 Axle 16 14 Electronics Black Box 1 15 Battery Cell 3 9 17 Static O-Ring 1

11 17 C C

6 8 9 10

B B

DO NOT SCALE DRAWING REVISION

TITLE: Left Half Assembly A A DWG NO. A3

SCALE:1:2 SHEET 4 OF 6 8 7 6 5 4 3 2 1 SOLIDWORKS Educational Product. For Instructional Use Only. 8 7 6 5 4 3 2 1 ITEM NO. PART NUMBER QTY. 1 Wave Generator Pin 2 Harmonic Drive Wave F 2 Generator Wheel 2 Adhesive Pad 15 F Harmonic Drive Wave 3 Generator Mount 1 Adhesive Pad 4 Flexible drive collet 1 Harmonic Drive 5 Output Spur Gear 1 6 Motor 1 E 7 Harmonic Drive 1 E Flexible Spline 14 8 Housing Left Half 1 M2 Pan X 7mm Head 9 Screw 7 5 10 Hobby Servo 1 12 11 Servo Cam 1 4 Helical Spur Trigger 12 Compound Input 1 13 D Gear 7 D 13 Helical Spur Trigger 1 Axle 16 14 Electronics Black Box 1 15 Battery Cell 3 9 17 Static O-Ring 1

11 17 C C

6 8 9 10

B B

DO NOT SCALE DRAWING REVISION

TITLE: Left Half Assembly A A DWG NO. A3

SCALE:1:2 SHEET 4 OF 6 8 7 6 5 4 3 2 1 SOLIDWORKS Educational Product. For Instructional Use Only. 8 7 6 5 4 3 2 1 ITEM NO. PART NUMBER QTY. 1 4mm Bearing SKF 624 1 2 Sliding Helical Clutch Gear 1 F 3 Crown Gear 1 F 4 Yaw Drive Beam 1 5 M2 Pan X 7mm Head Screw 1 6 10mm Bearing SKF 6000 1 7 M4 X 9mm Cap Head Screw 2 8 Freewheel Housing 1 9 Ratchet Output Gear 1 E 10 Ratchet Spring 1 E 11 Housing Right Half 1 12 Freewheel Ratchet Pawls 3 13 Part1^Right Hald assembly 1

D D

C C

9 8 6 11 2 4 3 5 B B

DO NOT SCALE DRAWING REVISION

TITLE: Right Half A Assembly A DWG NO. A3

SCALE: 1:1 SHEET 5 OF 6 8 7 6 5 4 3 2 1 SOLIDWORKS Educational Product. For Instructional Use Only. 8 7 6 5 4 3 2 1 ITEM NO. PART NUMBER QTY. 27 4 3 1 Housing Left Half 1 1 3 F 2 Rudder 1 F Protective Propeller 3 Ring 1 25 Rolling Linkage Top 4 Pin 1 5 circlip 35 14 6 Geared Top Linkage 2 7 Upper Jumping Beam 2 E E 2 8 Middle Linkage Brace 2 Geared Linkage 9 Bottom Left 1 21 10 Foot Linkage 2 Geared Linkage 11 Bottom Right 1 12 Front rolling Linkage 2 20 13 Knee Joint Pin Front 1 D D 14 Knee Joint Pin Rear 1 27 19 15 Knee Joint Spacer 2

7 22 16 Foot Front Pin 1 17 Foot Front Spacer 2 23 18 Foot Back Pin 1 19 Torsion Spring Right 1 M4 X 9mm Cap Head C 20 Screw 4 C 15 13 22 21 M3 X 18mm Screw 3 22 Spring Holder Beam 1 6 23 Torsion Spring Left 1 24 Bottom Spring Holder 24 Beam 1 25 Housing Right Half 1 B 27 M3 X 10mm Screw 3 B 10 DO NOT SCALE DRAWING REVISION

16 TITLE: Shell and Leg Assembly A A DWG NO. A3 18 11 12 17 5 9 8

SCALE: 1:1 SHEET 6 OF 6 8 7 6 5 4 3 2 1 SOLIDWORKS Educational Product. For Instructional Use Only.