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

Chapter 3.0 Vehicle Design
3.4 Reciprocating Chemical Muscle
Advantages of this version of the fourth generation RCM can be summarized as:
1. Vibrationless
2. Internal porting
3. Guaranteed extension synchronization
4. Idler Gear sees low force and has low inertia
5. Force applied along central axis with offset arms
6. Straight rack and idler gear teeth easier to machine
7. Piston shafts can't rotate (due to idler gear)
In addition, by blocking one of the actuator pistons and removing the spur gear, the RCM can be
made operate in a single ended mode. It can also be made to function in a “one-shot” mode. In
addition the entire system has been manufactured of materials similar in coefficient of thermal
expansion, in order to minimize seizures of close tolerance components. Special perfluoro
organic and diamond like coatings will be used for high wear areas and gasketing material in a
production version.
3.4.3 Sizing of the Entomopter-based Aerial Mars Surveyor
Many of the problems associated with the miniaturization of the terrestrial RCM actuator are
relaxed when considering the scaled up Mars version. Further, the reciprocation rate required of
the Mars RCM actuator will be less than half that required for the terrestrial version, so although
the inertias of the larger component masses will be greater, the forces will be mitigated due to
the smaller accelerations of those masses.
The sizing of the Entomopter for aerial Mars survey is driven by the constraints of the Mars
environment and choices made regarding the RCM, fuel type, wing parameters, and the baseline
mission. Variables to be considered in a first order sizing analysis include the following:
RCM Actuator:
• Single Cylinder Volume (liter)
• Piston Diameter (cm)
• Piston Area (typ) (square cm)
• Single Cylinder Throw (cm)
• Cylinder Pressure (N/m2)
• Temperature of Fuel Decomposition (°K)
• Reciprocation Frequency (Hz)
• Fuel Expansion Ratio (liquid-to-gas)
• Moles of Gas required per cycle (n=PV/RT)
• Liquid Fuel Expended per flap (both cylinders) (liters)
• Liquid Fuel Capacity per min of flight (liters/min)
• Liquid Fuel Weight consumed per minute of flight (kg)
• Linear Force of both Cylinders at full pressure (N)
• Linear-to-Rotational Cam-Follower Ratio
• Combined Rotational Force available (at wing root) (N)
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