Lunar Rover Convertible Mobility System (LRCMS) University of Wyoming May 11th, 2020 Miranda Threewitt Hali Martin Margaret Lichtenfels Craig Smith Zach Hunter Page 1 of 42 Abstract The Lunar Rover Convertible Mobility System (LRCMS) is a convertible chassis designed to be used for lunar missions into permanently shadowed regions (PSR) of the moon, primarily consisting of steep lunar craters. This design utilizes flexible members called compliant mechanisms that replace typical joints and reduce abrasive dust build-up in the chassis. The compliant mechanisms allow the chassis to bend into different positions for both explicit point steering and Ackerman style steering. Inside the chassis, linear actuators are used to push/pull the chassis into the different steering configurations. Using SolidWorks simulations, the resilience of the chassis was tested under static forces, cyclic forces, and extreme thermal conditions. The results showed that the chassis will perform as desired. In addition to the simulations, physical testing plans have been designed to gauge the system’s endurance and capabilities. Page 2 of 42 Table of Contents Abstract ......................................................................................................................................................... 2 Introduction................................................................................................................................................... 4 Background Information ............................................................................................................................... 4 Design ............................................................................................................................................................ 8 Outer Body ................................................................................................................................................. 8 Inner Body .................................................................................................................................................. 9 Payload Mounting .................................................................................................................................... 10 Weight Breakdown .................................................................................................................................. 11 Simulations .................................................................................................................................................. 12 Compliant Mechanisms ........................................................................................................................... 12 Static Steering Positions .......................................................................................................................... 14 Cyclic Steering Positions .......................................................................................................................... 16 Thermal Simulations ................................................................................................................................ 18 Testing Plans ................................................................................................................................................ 20 Mobility .................................................................................................................................................... 20 Environmental.......................................................................................................................................... 21 Structural ................................................................................................................................................. 21 Manufacturing Information ........................................................................................................................ 22 Conclusions .................................................................................................................................................. 23 References ................................................................................................................................................... 24 Appendices .................................................................................................................................................. 25 Appendix A. Dimensioned Drawing for Chassis Outer Body ..................................................................... 26 Appendix B. Dimensioned Drawing for Part 1.1 ........................................................................................ 27 Appendix C. Dimensioned Drawing for Part 1.2 ........................................................................................ 28 Appendix D. Dimensioned Drawing for Part 1.3 ........................................................................................ 29 Appendix E. Dimensioned Drawing for Part 1.4 ........................................................................................ 30 Appendix F. Dimensioned Drawing for push/pull bar ............................................................................... 31 Appendix G. Dimensioned Drawing for pin ............................................................................................... 32 Appendix H. Dimensioned Drawing for Extended Linear Actuator .......................................................... 33 Appendix I. Dimensioned Drawing for Testing Compliant Mechanism .................................................... 34 Appendix J. UW Projected Project Budget ................................................................................................. 35 Appendix K. Off Campus Competition Testing Plans ................................................................................. 40 Page 3 of 42 Introduction The following report describes the design and testing process for the Lunar Rover Convertible Mobility System (LRCMS), a convertible chassis that has the capability of assuming different configurations that allow for unique steering methods. This design is meant to be used on lunar exploratory missions with versatility for different payloads and mission types. Testing simulations offered insight into the system’s validity and capabilities. Additionally, physical testing plans have been designed for further work on this project. Background Information Mission Overview The mission objective chosen for NASA’s BIG Idea competition is to develop a mobility system that aids in the exploration of the moon’s permanently shadowed regions (PSRs) in search of ice or traces of water. The PSR that the mission is being designed around is the 21 km diameter Shackleton crater which is located near the south pole of the moon, as shown in Figure 1a. The walls of this crater have extremely steep slopes, as shown in Figure 1b, which poses a challenge for a rover attempting to climb into and out of the crater, especially if the regolith (abrasive lunar dust) is loose along the crater walls. (a) (b) Figure 1. (a) Location of Shackleton crater: lunar south pole. (b) Topographical representation of Shackleton crater [6]. The proposed mobility system, carrying a science payload, is designed to be delivered to the moon via a Peregrine Lunar Lander, pictured in Figure 2. Detailed information on the Peregrine Lunar Lander can be found in the “Astrobotic Peregrine Lunar Lander Payload User’s Guide.” The rover, consisting of the mobility system and the science payload, will be classified as deployable active, meaning it will detach from the lunar lander and perform independent mission tasks. The lander will land and release the rover Page 4 of 42 within 100 m of the chosen crater rim. From there, the rover will embark on its exploratory mission, fully charged from the lander. Figure 2. Peregrine Lunar Lander taken from “Astrobotic Peregrine Lunar Lander Payload User’s Guide” [1]. The LRCMS is designed to accommodate a variety of science payloads such as equipment for sample collection, sample testing, scanning and searching systems, or other similar systems with the intent of being versatile for use on a variety of missions. The rover itself is designed to handle maneuvering throughout the entire crater, including its steep inner walls. Such a design will allow the rover to collect samples and data within multiple craters over a given mission. Compliant Mechanisms Due to the invasive nature of the lunar dust, having pin joints on the lunar chassis is problematic. The need for such joints is minimized by using members known as compliant mechanisms that do not require a hinge, pin or bearing for motion. A compliant mechanism is a hinge-like member that gains its mobility from the deflection of flexible members rather than from movable joints only. Research dictated that designing a mechanism of our own for this project would be more intensive than anticipated. To minimize the time and labor to design such a member, an existing compliant mechanism was used instead. This mechanism would need to effectively rotate 45° in either direction from rest as well as being sturdy enough in the vertical direction to support the weight of the rover. The first mechanism that was of interest included a design from Brigham Young University and is shown below in Figure 3 from the online document “Design of 3D-Printed Titanium Compliant Mechanisms.” The reason this specific mechanism was appealing is the fact that it can flex 90° in either direction. This is more motion than the chassis design requires, but the reduction in stress extends the fatigue life of the hinge. This design falls short when it comes to vertical strength, as there are no connections that would make the hinge stiff in this direction and thus, would not be able to support the weight of the rover. Page 5 of 42 Figure 3. Titanium hinge with ± 90° of motion [2] . A mechanism that contains both vertical strength and ability to rotate as desired was found in the online document “Design of Large-Displacement Compliant Joints”. The dimensions were not specified in the design, so they were modified until they satisfied the project requirements. A dimensioned SolidWorks model of this compliant mechanism is shown below in Figure 4. Figure 4. A single dimensioned compliant joint design. The dimensions of the center plus-like cross-sections are most important in terms of ability to rotate, as these are the deforming pieces of the compliant mechanism. Furthermore, it is necessary to make sure the dimensions are scaled correctly so that the linear actuators will be able to deform the part. SolidWorks simulations were a helpful tool in determining exactly what these proper dimensions should be. The simulated load applied to this mechanism resulted in an angle change of about 45 degrees, which is the range we needed on the chassis mechanisms. The angle change of the mechanism is shown in Figure 5. These simulations specified the amount of force the motors will need to provide in order to deform the mechanisms and control the chassis. (a) (b) Figure 5. (a) Compliant mechanism top view before static load simulation (b) Compliant mechanism top view after static load simulation Page 6 of 42 Explicit Steering The challenge to design a mobility system for the lunar rover was first approached with the concept of explicit steering presented by Benjamin Shamah in his paper titled “Experimental Comparison of Skid Steering vs. Explicit Steering for a Wheeled Mobile Robot.” In this paper, Shamah explores a steering method that eliminates the need for traditional skid steering using a body that can convert into different wheel configurations as shown in Figure 6. This steering method appealed to the LRCMS project due to the amount of dust that is agitated in a conventional skid-steering method. Through an explicit steering model, the rover will minimize dust interference while also providing multiple modes of configuration for the optimal transport requirements. Figure 6. Explicit steering method graphic. Reprinted from Shamah, “Experimental comparison of skid steering vs. Explicit steering for a wheeled mobile robot,” pg.3 To implement this steering method, a custom chassis geometry was designed such that the chassis structure could be converted into different positions. The different configurations are shown below in Figure 7, which involves rigid members depicted in blue and collapsible joint members depicted in red. Through the geometry-specific design, the chassis can configure into a point steering system with a zero-turn radius, the main desired steering method of the rover. Even though a zero-turn radius will prevent the maximum amount of dust interference for the LRCMS, the rover has the additional ability to extend one side of the chassis while retracting the other to allow an Ackermann-style steering to avoid obstacles. Figure 7. Convertible chassis wheel configurations and steering methods. Page 7 of 42 Design Outer Body The outer body of the chassis is the component which gives the rover its convertibility. This is made possible by a combination of 20 compliant mechanisms arranged in a carefully designed geometry such that the compliant joints work with the intermediate members to arrange the rover’s wheels into different steering positions. The location of the mechanisms can be found in Figure 8a and a graphic of the outer body compliant mechanism configuration can be found in Figure 8b. (a) (b) Figure 8. (a) Location of compliant mechanism in the outer body of the chassis. (b) Graphic of the chassis outer body. To convert into an explicit point steering position, force must be exerted on locations 1, 2, 3, and 4 in Figure 8a until the wheels reach 45° from their original position. To convert into an Ackerman steering position, an outward force must be applied to locations 1 and 2 while an inward force is applied to locations 3 and 4, or vice versa based on the direction of the turn. The arrangement of the convertible bars was inspired by Figure 6 above from Shamah’s paper, but our arrangement ended up being a different configuration. Our original geometry for the bars can be found below in Figure 9. Page 8 of 42 Figure 9. Original dimensions of convertible chassis geometry. These proportions allow the chassis to bend into the configurations shown previously in Figure 7. After assigning these dimensions to the chassis components, the chassis was modeled to fit the dimensions. Later on, the entire model was scaled down slightly to an extent where the thickness of the walls and mechanisms matched the thickness of a common stock metal thickness, in this case 8mm, for ease of manufacturing. The dimensioned drawing of the scaled model can be found in Appendix A. Additionally, drawings for the individual components that make up the outer body can be found in Appendices B, C, D, and E. At the four corners of the outer body, small walls extend for wheel attachment. Here the motors can be mounted for the wheels to be directly and individually driven. Additional components such as batteries can be attached on the corner walls with the wheel motors or on top of the chassis above the convertible components. Inner Body The inner body design of this chassis is relatively simple as it consists of only actuators, batteries and connections. A linear actuator is a motor that creates motion in a straight line rather than in a circular motion like a conventional motor. In this design two L16-S miniature linear actuators are used to move the push bars that control the steering of the entire chassis. This specific linear actuator can be found on the Actuonix website. It requires 12 volts and has a thrusting force of 200 Newtons. The stroke length ( maximum length of extension) is 100 mm and the gear ratio within the actuator is 150:1. The maximum Page 9 of 42 speed of extension is 8 mm/s meaning it will take 12.5 seconds to fully extend. A photo of this actuator is shown below in Figure 10. Figure 10. L16-S miniature linear actuator used to control the chassis . These linear actuators are powered by two separate custom 10 cell, 12-volt battery packs from batteryplus.com, one for each actuator. The images shown in Figure 11 depict how the actuators and battery packs are situated within the chassis. The chassis is “at rest” in these figures, meaning that the actuators are halfway extended and applying no force inward or outward. (a) (b) Figure 11. (a) Side view of actuators and battery packs mounted to stationary bars. (b) Top view of actuator and push bar design. The battery packs and actuators are mounted to the stationary points on the chassis using standard brackets and bolts. The battery packs are located just below the actuators for easy connections, and the actuators are connected to the push bars using a simple pin. This pin connection is located about 5mm from the end of the actuator’s extending arm. It is also important to note that the actuator is mounted to the right side of the chassis to control the movement of the left half of the chassis and vice versa. There are small rectangular cutouts in the stationary bars to ensure that the push bars do not interfere with steering when the actuators are fully extended. The actuators and battery packs are thin enough that they also do not interfere with steering when the actuators are fully retracted. A dimensioned drawing of the inner body components can be found in Appendices F, G, and H. Payload Mounting This chassis is designed to carry a variety of different payloads including equipment for sample collection, sample testing, scanning and searching systems, etc. These payloads will not only differ in purpose, but size and shape as well, and therefore will have their own unique mount. There are four stationary points on the chassis that will act as building blocks for the mounts. These points are shown Page 10 of 42 below in light blue in Figure 12a. All four of the blue spots are raised 5mm above the rest of the rover specifically for mounting payloads. The purpose of the raised edges is to ensure that nothing interferes with the movement of the chassis. The next picture, Figure 12b, shows how a flat plate can be placed onto these points without affecting chassis movement and steering. (a) (b) Figure 12. (a) Top view of actuators and battery packs mounted to stationary bars. (b) Top view of payload mounting plate . Weight Breakdown With an overall weight limit of 15 kg for transport aboard the Peregrine Lander, our goal was to make the chassis as light as possible so that most of the weight could be allocated to other systems such as wheels and motors, power, and science payloads and devices. A weight breakdown of our system can be found in Table 1 which shown that our system only weighs about 2.6 kg leaving about 12.4 kg for other systems. Table 1. Weight breakdown the LRCMS components. Item Weight Linear Actuators x2 168 grams Battery pack x2 100 grams Chassis Frame 2300 grams Actuator and Battery 20 grams mounts Total Weight 2588 grams Page 11 of 42 Simulations Compliant Mechanisms The design of the chassis is dependent on the use of the flexible members throughout the chassis. These compliant mechanisms need to exhibit the necessary strength and durability to support the rover while also being flexible enough to conform to the different configurations. It is very important that the material chosen matches the needs of the project and can handle the various design considerations. We compared several different materials and simulated the different results. The first material we considered was 6061 Aluminum due to its high resistance to thermal strain with a melting point of 582°C (1080°F). This would work well through the various temperature changes that the rover would experience over the course of the mission. Also, as an aluminum alloy it is relatively lightweight and reasonably easy to machine. This means we would be able to adequately finish the surface of the compliant mechanisms to ensure that there are no localized stress points or defects. Unfortunately, with a modulus of elasticity of 68.9 GPa, it is very difficult to bend and would require a force of almost 200 N to deform the mechanisms across the full range of motion. The second material we considered was Thermoplastic Polyurethane (TPU). This material is a rubber-like 3D printed material that is accessible through the University’s Student Innovation Center. It is cost effective and extremely easy to bend while being able to maintain structural integrity. It is unable to withstand the temperature ranges we expect over the course of the mission but would serve as a suitable material choice for local Earth-based movement. We also considered using various grades of stainless steel due to the thermal resistance and flexibility. Stainless steel can withstand the different temperature ranges and is even tough enough to resist the abrasiveness of the lunar dust. The drawbacks include the fact that stainless steel happens to be a very heavy material, which is not ideal for spaceflight and would be extremely difficult to machine, especially without inherent deformations in the structure. The last material we considered was 5052 Aluminum. This aluminum can operate under the different environmental parameters and is even known in industry for its willingness to deform. It is a very light, easy material to machine/weld which would allow it to be properly finished for lunar exploration. It is, however, prone to strain hardening and thermal elongation which could result in internalized stress concentrations in our chassis. Despite the considerations, it is the material we have chosen to use in our design. The specific geometry of our design will have stress concentrations similar to the model shown in Figure 13 taken from “Design of Large-Displacement Compliant Joints” [5]. We have also determined that the displacement of the joint would not be significant enough to fatigue the material over the course of the mission. Page 12 of 42 Figure 13. An example of expected stress concentration locations taken from “Design of Large- Displacement Compliant Joints ”[5]. Figure 14, shown below, confirms the results for the stress locations above. The stress will be localized in the corners of the plus-like crosshairs. The static simulation was run for 5052 aluminum with an applied force of 20 N which was able to show the resulting deflection necessary for the chassis to function. (a) (b) Figure 14. An example of stress concentration locations taken from simulations seen from (a) top view and (b) model view. The simulation gave the resulting stress as shown in Figure 15. The resulting deformation is localized in the locations we expected and are well below the yield strength for our material. This shows that 5052 aluminum is a reasonable choice for the implementations of our design. We intend to use the testing apparatus described in a later section to further verify our design using physical testing methods. Page 13 of 42 (a) (b) Figure 15. (a) Simulated stress concentrations of a static loading of a compliant mechanism with an applied force of 20N (b) enlarged view of the static stress concentrations . Static Steering Positions After conducting simulations on individual compliant mechanisms, we began full-body testing simulations starting with the outer body static simulations for the steering positions for a 5052-aluminum chassis. We implemented this by applying forces to push/pull bars located in the inner body to verify that the chassis would transform into the desired geometries and to find out what force would be needed to reach the desired wheel positions. The maximum capabilities of high-displacement deformation in SolidWorks allowed our chassis to reach a maximum of 30° wheel positions with 120 N of force applied to each inner push/pull bar; deformation past this 30° position would require testing on a physical prototype due to the limitations of high deformation in the software. The resulting configuration of this deformation can be found in Figure 16a and 16b. Page 14 of 42 (a) (b) Figure 16. (a) Top view of explicit steering position s tatic simulation. (b) Graphic of explicit steering position static simulation. The stresses resulting from the deformation of the chassis are concentrated in the crosshairs of the compliant mechanisms and are higher in the mechanisms that are deformed further. These stresses, however, remain well below the yield strength of the material, as shown in Figure 17 below. Figure 17. Snapshot of compliant mechanisms under stress from deformation. Page 15 of 42 This simulation was repeated for the Ackerman style steering position with similar results. The deformation results can be seen in Figure 18a and 18b. Once again, this is the maximum deformation that is allowed by the SolidWorks software so further deformation testing would have to take place on a physical prototype. (a) (b) Figure 18. (a) Top view of Ackerman steering position static simulation. (b) Graphic of Ackerman steering position static simulation. Cyclic Steering Positions Building off the static simulations, a cyclic fatigue simulation was created for the chassis extending and retracting throughout the length of the mission. A single cycle considers both an extension and retraction of the chassis using the force required for the range of motion used in the static simulations above. Figure 19 presents the results on the chassis after 1,000 cycles, which is displayed as a color gradient for damage percentage. The simulation results show that barely any damage occurs to the main structural members of the chassis; almost all the chassis is displayed in blue, representing 0.1% damage after 1000 cycles. It is, however, not the same case for the compliant joints of the chassis. Page 16 of 42 Figure 19. Cyc lic loading simulation displaying damage percent data after 1000 cycles . Figure 20 shown below displays larger images of the respective colored borders in Figure 19 above for a detailed analysis of the joints themselves. As the chassis extends and retracts, the joints will start to deteriorate and weaken. The color gradients of red and yellow/green display that the centers of the compliant mechanisms experience the most damage as the rover is configured into different positions. Figure 20. Enlarged image of damaged joints from Figure 19. The fatigue simulation was conducted for a various number of cycles ranging from 2 to 1,000 cycles. This data was then constructed into a single plot shown in Figure 21 to determine the maximum Page 17 of 42 number of cycles that the chassis can experience during the mission. These compliant joints quickly deteriorate. Most structures are designed to last well over one million cycles, if not designed to experience a small enough force to allow an “infinite life-cycle.” This condition cannot be met for this design due to the amount of force required to fully extend/retract the chassis. Instead, the joints already experience 10% damage after 500 cycles. Even though this problem presents itself, implementing careful and strategic movement plans while on the moon will mitigate the issue. Movements only when direly needed to move past an obstacle will be implemented. In the hypothetical case that the rover only needs ten cycles of the chassis to perform its daily functions (which can be achieved with careful planning), the chassis will last 50 days before 10% damage occurs to the compliant joints which is well above the length of time for the mission. Figure 21. Joint damage percentage depicted through a range of cycle numbers. Thermal Simulations The body of the rover must be able to withstand a temperature range of –200°C to 100°C in order to survive the lunar environment [6]. Temperature simulations were run to ensure that the body would not break or deform at these temperatures. Figure 22 depicts the von Mises stresses that the body would experience at 100°C. These stresses are highest at 79 Pa in the red zones which can be seen in the corner compliant mechanisms. The center compliant mechanisms experience less stress at around 33 Pa. These values are much below the yield strength of 195 MPa. Page 18 of 42 Figure 22. Stresses in the chassis due to a 100° C environment. Figure 23 illustrates the effect of a -200°C environment on the rover body. This more extreme temperature results in higher overall von Mises stresses. The corner compliant mechanisms experience a maximum of 237 Pa, and the center compliant mechanisms feel around 79 Pa. Again, these values are well below the yield strength. Figure 23. Stresses in the chassis due to a -200° C environment. Page 19 of 42 Testing Plans Mobility Since mobility is the focus of the LRCMS design, the mobility testing planned for the rover to undergo is extensive in order to provide detailed information on the system’s capabilities. This testing involves different types of terrain, different obstacle configurations, and analyzing the steering capabilities of the system. The desired outcome of these tests is a set of data describing the exact capabilities of the rover such that a mission’s navigation could be fully informed when planned. The first set of mobility tests takes place on a custom tilt platform constructed at the University of Wyoming with a range 0° to 60⁰. The plan includes direct driving, driving over obstacles, and steering around obstacles while carrying a 12.4 kg payload. The break-down of the testing is shown in Figure 24. Figure 24. Diagram of mobi lity testing plan for the L RCMS. Tilt platform testing can be repeated with payloads of different sizes, shapes, and mass distributions. The equipment needed for this testing is the custom-built tilt platform, the fully functioning LRCMS including motors, a battery, a remote controlling system, and custom-made obstacles of a range of shapes and sizes. The full set of tilt platform testing is planned to take place at the University of Wyoming. The second part of mobility testing is gauging travel capability over obstacles in loose terrain. The same obstacle and steering procedures will be carried out over a flat bed of sand. The final set of mobility testing takes place at the North Sand Hills Recreation Area outside of Walden, CO. This testing would allow the team to better analyze the LRCMS’s ability to navigate simulated lunar craters and dunes. Page 20 of 42 Environmental A future testing plan that utilizes the University of Wyoming’s environmental chamber was created for the continuation into the research of this design. While computational simulations have been created for static, cyclic, and thermal tests, an environmental chamber would allow the testing of our chassis under different pressure and temperature ranges. This is an important consideration since our simulations do not account for the differences in these parameters between Earth and the moon. The environmental testing of the full-body rover involves performing all functions of the rover over multiple days and inspecting for damages, with a comparison to our tabulated simulation results. As a starting point for the environmental tests, the chassis would perform its functions at 100,000 ft altitude for temperatures ranging from –70 °C to 190 °C, at 150,000 ft altitude for temperatures ranging from 20 °C to 200 °C, and at 200,000 ft altitude for temperatures ranging from 20 °C to 200 °C. The chamber at the University of Wyoming is not capable of the specified testing plans, so they would be altered so the parameters that that are achievable would be tested. Structural To test the structural integrity of the compliant mechanisms, our testing plan is designed to cyclically test them and determine fatigue life. In this plan, three set of 5 mechanisms made from different materials would be tested. This would confirm our material selection. A load frame adapter would be constructed to attach the compliant mechanisms to the frame and actuator. Figure 235a shows an example of the adapter, and Figure 25b demonstrates how the arm extending off the compliant mechanism would be attached. An eyehook and rated rope would be used to affix the mechanism to the actuator from which it would be cyclically loaded at 20 N. (a) (b) Figure 25. (a) Load frame adapter example . (b) Graphic of load frame adapter with compliant mechanism. Page 21 of 42 This figure, above, shows a load frame adapter that could be designed and used specifically for the compliant mechanisms. The compliant mechanism would be fixed, with the arm extending out. An eye hook would be used to attach a rope to the actuator, which would cyclically load the mechanism. The full body rover would also need to be rated for its load bearing capabilities. This would involve a simple test of increasing force applied to the body until failure. A fully dimensioned drawing of the individual compliant mechanism testing model can be found in Appendix I. Manufacturing Information The complete budget for the LRCMS is broken up into several sections, all of which are detailed in Appendix J. We have estimated that manufacturing an entire LRCMS would take roughly 1.5 months broken down into 1-week segments with deliverables for each stage. The first objective is to procure the materials for machining which we estimate to be about $100 for 5052 Aluminum. The machining stage is estimated to take about a week and about $200 for a single completed chassis. Afterwards, in the welding stage, the machined parts are to be welded together by the members of the team. Overall, the process for manufacturing a single chassis will cost about $750. In the machining stage, the raw aluminum sheet metal will be machined down to create each of the individual components of the design. The compliant mechanisms are designed to be easily machinable and will likely be carried out by the University of Wyoming’s machine shop. Some of the machining can be done by the team members themselves using other CNC machines around campus which will likely help to minimize the cost. For the welding stage, the team members will tig weld the pieces together. This will require us to purchase filler and will be easily accomplished within the week we have allotted. While this portion of the project is being undertaken, the team members who are not working on welding will oversee preparing code and other components for the assembly stage. In the assembly stage, all of the internal components are attached. The linear actuators are connected via pins and are attached to the internal frame as seen in Figure 11. The driving Arduino will be attached to a central stationary location. The motors that have been taken from previous rovers will also be attached on the exterior corners along with the wheels. All of these internal components will be examined for potential problems with wiring and space constraints. From this point, the LRCMS will be completely functional and the code that was developed by the team in the welding stage will be uploaded to the Arduino. This will then make the full rover capable of physical testing and even limited movement controlled through its micro-processing unit. Page 22 of 42 Conclusions Based on the SolidWorks simulations that were conducted in place of physical testing, the LRCMS is a successful design. The use of compliant mechanisms offer a great solution to prevention of dust build- up and enable the chassis to convert into different configurations. The use of explicit point steering and Ackerman style steering improves overall maneuverability of the vehicle for easier transit over the lunar surface. Mass, size, and functionality goals were all met with an extremely lightweight mass of less than 3 kg, a size of 13.5” x 14”, and a low center of gravity for steep slope travel. The simulation-based testing produced results that confirmed our design and physical testing plans are in place for further investigation into this effectiveness and capabilities of this design. Page 23 of 42 References 1. “Astrobotic Peregrine Lunar Lander Payload User Guide.” Peregrine, June 2019. 2. L16-s Miniature Linear Actuator With Limit Switches: Actuonix https://www.actuonix.com/L16-S-Linear-Actuator-p/l16-s.htm?1=1&CartID=0 3. Shamah, Benjamin. “Experimental Comparison of Skid Steering Vs. Explicit Steering for a Wheeled Mobile Robot.” The Robotics Institute Carnegie Mellon University, Mar. 1999. 4. Toupet, Oliver, et al. Traction Control Design and Integration Onboard the Mars Science Laboratory Rover. 2013, Traction Control Design and Integration Onboard the Mars Science Laboratory Rover. 5. Trease, Brian P, et al. “Design of Large-Displacement Compliant Joints.” 6. Ask an Astronomer. (n.d.). Retrieved from http://coolcosmos.ipac.caltech.edu/ask/168-What-is-the- temperature-on-the-Moon- 7. Linß, S., Henning, S., & Zentner, L. (2019, April 3). Modeling and Design of Flexure Hinge-Based Compliant Mechanisms. Retrieved from https://www.intechopen.com/books/kinematics-analysis- and-applications/modeling-and-design-of-flexure-hinge-based-compliant-mechanisms 8. Merriam, E. G., Jones, J. E., & Howell, L. L. (n.d.). Design of 3D-Printed Titanium Compliant Mechanisms. 9. Pavlovi´c, N. T., & Pavlovi´c, N. D. (n.d.). Mobility of the compliant joints and compliant mechanisms. Belgrade. Retrieved from https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150004057.pdf 10. Spudis, P. D., Bussey, B., Plescia, J., Josset, J.-L., & Beauvivre Ste ṕ hane. (2008). Geology of Shackleton Crater and the south pole of the Moon (L14201 ed., Vol. 35). 11. Thomson, B. J., Bussey, D. B. J., Cahill, J., Spudis, P. D., Neish, C., & Patterson, G. W. (2011). The Interior Of Shackleton Crater As Revealed By Mini-Rf Orbital Radar. 42nd Lunar and Planetary Conference. 12. Colwell, J. E., Batiste, S. E., Sture, S. E., Hora ́nyi M., & Robertson, S. (2007). Lunar Surface: Dust Dynamics And Regolith Mechanics. American Geophysical Union. 13. Bickel, V. T., & Kring, D. A. (2019). Lunar South Pole Boulders and Boulder Tracks:Implications for Crew and Rover Traverses. Lunar and Planetary Institute. Page 24 of 42 Appendices Appendix A. Dimensioned Drawing for Chassis Outer Body Appendix B. Dimensioned Drawing for Part 1.1 Appendix C. Dimensioned Drawing for Part 1.2 Appendix D. Dimensioned Drawing for Part 1.3 Appendix E. Dimensioned Drawing for Part 1.4 Appendix F. Dimensioned Drawing for push/pull bar Appendix G. Dimensioned Drawing for pin Appendix H. Dimensioned Drawing for Extended Linear Actuator Appendix I. Dimensioned Drawing for Testing Compliant Mechanism Appendix J. UW Projected Project Budget Appendix K. Off Campus Competition Testing Plans Page 25 of 42 Appendix A. Dimensioned Drawing for Chassis Outer Body Page 26 of 42 Appendix B. Dimensioned Drawing for Part 1.1 Page 27 of 42 Appendix C. Dimensioned Drawing for Part 1.2 Page 28 of 42 Appendix D. Dimensioned Drawing for Part 1.3 Page 29 of 42 Appendix E. Dimensioned Drawing for Part 1.4 Page 30 of 42 Appendix F. Dimensioned Drawing for push/pull bar Page 31 of 42 Appendix G. Dimensioned Drawing for pin Page 32 of 42 Appendix H. Dimensioned Drawing for Extended Linear Actuator Page 33 of 42 Appendix I. Dimensioned Drawing for Testing Compliant Mechanism Page 34 of 42 Appendix J. UW Projected Project Budget The budget breakdown summary for completing the rover construction and testing using University of Wyoming facilities is shown by the pie chart in Figure J1. Figure J1. Projected project budget for LRCMS construction and testing. The largest cost of approximately $600 is making multiple compliant mechanisms out of different materials to complete fatigue testing on. The warmer colors are the cost of building the rover body, which totals $750. The remainder of the budget goes towards testing. A more detailed layout of our past expenses and projected expenses can be found in Tables J1, J2, J3, and J4. Page 35 of 42 Table J1. LRCMS budget summary. LRCMS Budget Senior Design Total (YTD) 2019-2020 Expenses Actual Budget Remaining $ Remaining % First Semester Funds $414.46 $400.00 ($14.46) -3.61% Material for Rover $79.68 $100.00 $20.32 20.32% Machining Costs $0.00 $200.00 $200.00 100.00% Linear Actuators $0.00 $300.00 $300.00 100.00% Material for Cyclic $94.57 $200.00 $105.43 52.72% Testing models Liquid Nitrogen $0.00 $140.00 $140.00 100.00% Adapter $0.00 $100.00 $100.00 100.00% Tig Welding Filler $0.00 $25.00 $25.00 100.00% Microcontroller Kit $0.00 $70.00 $70.00 100.00% Fasteners $0.00 $35.00 $35.00 100.00% Testing Apparatus $0.00 $100.00 $100.00 100.00% Miscelaneous Funds $0.00 $150.00 $150.00 100.00% Unused Funds from $0.00 $1,980.00 $1,980.00 100.00% Grants Total $588.71 $3,800.00 $3,211.29 84.51% Page 36 of 42 Table J2. LRCMS fall semester budget. LRCMS Fall Senior Semester Total Design Budget 2019-2020 Remaining Expenses Actual Budget Remaining % Date $ Paddles $8.25 $10.00 $1.75 17.50% 11/5/2019 Wheel $27.00 $30.00 $3.00 10.00% 11/5/2019 Compliant Joint $13.25 $15.00 $1.75 11.67% 11/11/2019 Wheel Hub $9.00 $10.00 $1.00 10.00% 11/19/2019 Compliant Joint $13.25 $15.00 $1.75 11.67% 11/21/2019 Replacement Joint $7.75 $5.00 ($2.75) -55.00% 12/3/2019 Joint $7.75 $5.00 ($2.75) -55.00% 12/4/2019 Paddle Wheel updated $31.50 $30.00 ($1.50) -5.00% 1/9/2020 Ultem Compliant $13.75 $15.00 $1.25 8.33% 1/10/2020 Mechanism Wheels (RC) $129.25 $120.00 ($9.25) -7.71% 1/10/2020 Wheels Slanted $125.25 $120.00 ($5.25) -4.38% 1/10/2020 Treads (RC) RC Car $28.46 $25.00 ($3.46) -13.84% Total $414.46 $400.00 -$14.46 -3.62% Page 37 of 42 Table J3. LRCMS spring semester budget. Senior LRCMS Spring Total Design Semester Budget 2019-2020 Remaining Remaining Expenses Actual Budget Date $ % Material for Rover $79.68 $100.00 $20.32 20.32% 3/5/2020 Material for Cyclic $94.57 $200.00 $105.43 52.72% 3/5/2020 Testing Models Machining Costs $0.00 $200.00 $200.00 100.00% N/A Linear Actuators $0.00 $300.00 $300.00 100.00% N/A Liquid Nitrogen $0.00 $140.00 $140.00 100.00% N/A Adapter $0.00 $100.00 $100.00 100.00% N/A Tig Welding Filler $0.00 $25.00 $25.00 100.00% N/A Microcontroller Kit $0.00 $70.00 $70.00 100.00% N/A Fasteners $0.00 $35.00 $35.00 100.00% N/A Testing Apparatus $0.00 $100.00 $100.00 100.00% N/A Miscelaneous Funds $0.00 $290.00 $290.00 100.00% N/A Total $174.25 $1,560.00 $1,385.75 88.83% Page 38 of 42 Table J4. LRCMS funding sources. LRCMS Senior Design Funding Total 2019-2020 Sources Expenses Actual Budget Remaining $ Remaining % NASA Space Grant $174.25 $1,000.00 $825.75 82.58% Fund UWEFE Fund $0.00 $2,500.00 $2,500.00 100.00% Senior Design Fund $414.46 $300.00 ($114.46) -38.15% Total $588.71 $3,800.00 $3,211.29 84.51% Page 39 of 42 Appendix K. Off Campus Competition Testing Plans The following testing plans were developed to ensure that the rover would successfully operate in all environmental conditions on the moon. These plans would be used specifically for the NASA Big Idea Challenge competition at NASA facilities. They are included in the report to address the complexity of testing required for a lunar mission, and to guide future student teams in their competition testing plans. Humidity Marshall Space Flight Center can provide the capability to test humidity, pressure changes, and some temperature ranges. The TH1 would be used to test thermal humidity from 0%-90% at ambient temperature from -70 to 190 °C. This involves a half day of set up and several days of testing to determine if any damage occurs. Temperature The rover must withstand in-transit and surface temperatures ranging from approximately -180 °C to 110 °C. To simulate this, the Space Environment Simulator (SES) at Goddard would be used to mimic the vacuum and temperatures. The SES uses liquid nitrogen and helium to reach the low temperatures and vacuum pumps to remove most of the air. This test takes several months and could likely be done in conjunction with other payloads, reducing cost. SES is 40 feet tall and has a 27-foot diameter, which would easily accommodate multiple experiments. The rover would be cycled through the entire temperature range to ensure it did not break, and it also would be operated at the extreme temperatures to test functionality. A fatigue test could also be performed on the rover’s compliant mechanism at the extreme temperature to confirm simulation results. Pressure The rover needs to withstand an in-transit pressure drop rate of -6.2 kPa/s and space environment pressure of 6.7*10-5 kPa. The V11/RAC Launch Simulation would be used to simulate this. Thermal altitude chambers can be used to create atmospheric flight conditions. The chambers account for low pressures, extreme temperatures, and humidity. Small components of our design will be tested in the TA3 with the largest altitude of 200,000 ft and from ambient temperature to 200 °C. The entire rover will be tested in TA1 which can test up to 100,000 ft from -70 to 190 °C. Two days would be needed to set up this testing and one day to run the testing. The rover would be cycled through the pressure changes for the duration they occur to see if any damage occurs. Temperature and humidity would be controlled. Radiation Radiation effects can cause major complications for materials and electronics in space. The three main considerations are single event effects, effects that worsen with time, and long-term radiation. Page 40 of 42 Single event effects are radiation damages that occur when a circuit is pierced by a burst of energy from a cosmic ray or from a solar particle. These particles deliver large amounts of energy into electronics, which corrupts data and computers. Over time, particles collect on the surface and build up charge. This creates static which damages electronics. The total dose of radiation wears down materials. These radiation effects could be tested on the rover at Radiation Effects Facility housed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The goal of testing is to reach a point of slow degradation in order to achieve what the rover can tolerate for the time it will be in space. The rover will have to endure a radiation environment of 20 rads/day for 3-15 travel days and 1 rad/day for 14-38 travel days. The testing mimics radiation including the constant irritation of the solar wind, the radiation belts, solar flares and cosmic rays. The majority of the rover is made of aluminum, which is often used to shield equipment from radiation, making it an excellent material choice. Three days would be spent at the facility setting up the testing parameters. The Center’s simulation software would be used to obtain radiation parameters for testing through simulating the environment that the rover will experience. Three rovers would be used for testing. One would undergo an exposure of 20 rads/day for the minimum days needed to answer how it will perform for a total of 15 days. The second rover would undergo an exposure of 1 rad/day for the minimum days need to determine how it will perform for a total of 38 days. The third rover would be exposed to the maximum expected total radiation dose of 1 krad. These tests will be used to calculate a prediction of how often an encounter with a highly charged particle will occur. The 2Mev Damage Study Accelerator would be used to study solar wind effects. Acceleration Testing The Peregrine Lunar Lander, which our system would be transported on, will undergo a wide acceleration range, the most severe of which will occur during launch. The Ground Research Facilities at Ames has a 20 G Centrifuge that would be used to test how our rover holds up during takeoff, flight, and landing. The in-transit acceleration range can be seen in Figure K1. Two days would be used to set up the test and one day to run it. Figure K1. Acceleration experienced by Peregrine Lunar Lander. Reprinted from “Peregrine Lunar Lander Payload User’s Guide”, 2019, p. 32. Page 41 of 42 Frequency and Shock Testing Finally, the frequency and shock experienced during launch, in-transit, and during landing must be considered. The LRCMS would undergo frequency and shock testing at the vibration and acoustics facilities at Johnson Space Center. The range of conditions experienced will be based on the information given by the Peregrine Lunar Lander Payload User’s Guide, which is shown in Figure K2. Figure K2. Frequency and acoustics experienced by Peregrine Lunar Lander. Reprinted from “Peregrine Lunar Lander Payload User’s Guide”, 2019, p. 33. Page 42 of 42