Phase II Final Report - NASA's Institute for Advanced Concepts

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Planetary Exploration Using Biomimetics An Entomopter for Flight on Mars now very low, itself being a function of the expulsion of gases in front of each piston as they pass through the restrictions of the internal porting. Frame 8 shows the split pistons in a static position at the end of their fully contracted throws. Once again the volume is unchanging and the pressure will rise (this time at point B) as gas mass continues to flow into the mechanism (see Frame 9). When the pressure exceeds the holding force of the spool, the spool will move suddenly to the left and the process starts over (Frames 10 - 12). An oversized working model was constructed with a polycarbonate housing to allow inspection of the internal kinematics. This is shown in Figure 3-141. Although this system functioned, it was not consistent, requiring tuning of the spool holding force/friction at different pressures. Reliable operation was improved with the addition of poppet valves keyed to piston position (shown externally in Figure 3-141). In this configuration both single-ended and double-ended operation were demonstrated. Figure 3-141: Acrylic Kinematic Visualization Testbed Further examination of the timing revealed that in spite of the symmetrical design, differences in piston-bore friction caused the pistons to reach full extension/retraction at slightly different times. This could be tuned and controlled through friction reduction techniques (diamond coatings, etc.) and higher levels of fabrication precision but a desired goal was to make the RCM inexpensive and robust in the face of varying fabrication tolerances and environmental conditions (principally temperature variations). Effort was therefore begun to make a third iteration that would guarantee symmetrically equal and opposite motion of the split pistons at any pressure over a range of pressures, and at any operational speed. 3.4.2.1 Improved Design for Guaranteed Low-tolerance Symmetry The fourth generation RCM evolved from the original third generation base mechanism consisting of two lower pair slider joints (piston and valve spool) which had a single degree of freedom, 160 Phase II Final Report
Chapter 3.0 Vehicle Design 3.4 Reciprocating Chemical Muscle providing low friction by spreading the wear over the bearing contact surfaces with narrow clearances which facilitated good conditions for lubrication and tight constraint of the motion. As stated above, initial efforts under the present grant focused on the development of a scaled up model manufactured with transparent polycarbonate and larger tolerances to intentionally magnify effects of manufacturing out-of-tolerance, large temperature changes, and prolonged wear. The clear polycarbonate body allowed for quick and precise understanding of performance since the movements of the internal components could be monitored visually in real time. The original third generation configuration had only two lower pair joints (piston and valve spool) without fixed joints in between, and allowed for a minimal control loop. One of the major improvements over the previous third generation design is the fourth generation RCM valving control having two separate pistons for the extend and retract motions. This was a large departure from the original generations of RCM, and it was done in order to minimize or almost totally eliminate the moments of inertia of action and reaction between the RCM body and the rest of the RCM actuator system. In the third generation RCM the valve actuation was directly (and externally) coupled to the piston pair and cycle speed was directly proportional to gas volume/pressure and the natural harmonics of the kinematic system. To assure positive action that has timing independent of piston friction, a pneumatic control valve actuation gated by a pilot valve directly machined on the pistons shaft was used. In this manner the actual shifting of the control (spool) valve is directly linked to piston shaft position, however (unlike the third generation devices) no mechanical linkages exist between the piston shaft and control valve, other than pneumatic pilot pressure. The result is positive valve control with no external parts or physical internal linkages. Vibration is eliminated and the resulting RCM is a single piece unit with equal and opposite-acting piston actuators, a single input pressure port, and a single waste gas exhaust port. In order to avoid out-of-timing scenarios, the two piston shafts were internally mechanically linked in their extend/retract trajectories by a spur gear mounted in a rack and pinion fashion between both (rack portions of the) shafts as shown in Figure 3-142. This new design architecture controls speed by modulating inlet pressure or exhaust volume. Regardless of the speed of reciprocation (even when transitioning between different reciprocation speeds) the actuator extension is equal and opposite from each end of the RCM. Forces are balanced between the two actuator pistons because they share a common pressure source. Axial vibration is eliminated for all operating conditions. 161
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Planetary Exploration Using Biomime
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Table of Contents Table of Contents
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List of Tables List of Tables Table
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List of Figures List of Figures Fig
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List of Figures Figure 3-54: Pressu
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List of Figures Figure 3-138: Stere
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List of Figures Figure 4-24: Averag
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List of Contributors List of Contri
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Executive Summary Executive Summary
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Chapter 1.0 Introduction Chapter 1.
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Chapter 1.0 Introduction Figure 1-2
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Chapter 1.0 Introduction 1.1 Histor
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Chapter 1.0 Introduction 1.2 Origin
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Chapter 1.0 Introduction 1.3 Missio
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1.3.3.1 Surface Imaging The Entomop
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Chapter 2.0 Entomopter Configuratio
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Chapter 3.0 Vehicle Design 3.1 Wing
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3. Density: 1.40E-2 kg/m 3 4. Press
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Chapter 3.0 Vehicle Design 3.6 Powe
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Chapter 4.0 Entomopter Flight Opera
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Chapter 5.0 Potential Payload Funct
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Chapter 6.0 Media Exposure 6.1 Intr
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Chapter 6.0 Media Exposure 6.3 Onli
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Chapter 6.0 Media Exposure 6.6 Spec
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Chapter 7.0 Conclusion Chapter 7.0
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Appendix A: Mars Atmosphere Data JP
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Appendix A: Mars Atmosphere Data Ge
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Appendix A: Mars Atmosphere Data Ge
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Appendix A: Mars Atmosphere Data Ma
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Appendix B: Sizing Results Appendix
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Appendix B: Sizing Results 30 Wing
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Appendix B: Sizing Results 16 Wing
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Appendix B: Sizing Results Length 0
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Appendix B: Sizing Results Lenght 0
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Appendix C: List of References Appe
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Appendix C: List of References 41.
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Phase II Final Report - NASA's Institute for Advanced Concepts

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