Thrust 2: Compactness

Title

2A: Chemofluidic Hot Gas Vane Motor/Pump

Project Leader

Prof. Michael Goldfarb (Vanderbilt)

Statement of Project Goals

The goal of this project is to develop, demonstrate, and characterize the performance of a monopropellant-powered vane motor for use in high bandwidth actuation of a hydraulic pump.  The first five years will primarily involve development of the motor, which is expected to deliver a continuous power in excess of 1000 W/kg (approximately a factor of five better than rare-Earth magnet brushless electric motors).  The second five years will integrate the motor into a closed-loop-controlled throttle-less hydraulic actuator to provide compact hydraulic power for small-scale fluid-powered systems, such as compact robots.

Project Role in Support of Strategic Plan

One of the stated objectives of the Center is to develop compact (i.e., human-scale) fluid powered systems.  Project 2A provides a means of efficiently powering and controlling human-scale fluid-powered systems.  The chemofluidic hot gas vane motor is not subject to the quenching or scavenging problems found in a small-scale IC engine.  In addition, unlike an IC engine, it can provide bidirectional, high-bandwidth motion and high torque at zero speed (rpm).  As such, the motor can be used for throttle-less actuation, therefore bypassing the fluid heating and inefficiency problems that plague the systems mentioned above.  Further, the liquid propellant that powers the proposed approach is not flammable, the motor can be easily started and stopped, has zero fuel consumption on idle, does not require air (i.e., can be used underwater or in space), and has completely safe reaction products (i.e., can be used indoors).  The objective of project 2A is to develop, demonstrate, and energetically characterize a complete, closed-loop controlled, throttle-less actuation system in a human-scale robot (specifically in the compact rescue crawler test bed).  If successful, project 2A will enable the use of high power density fluid-power actuators in human-scale robots, and thus will contribute directly to the fulfillment of the Center's vision.

Description and Explanation of Research Approach

Challenges in the development of the motor include friction, thermal expansion, and sealing.  These issues are being addressed by model-based design, experimental assessment, and design iteration.  The extent to which these issues can be mitigated will determine the promise of this technology.  With regard to throttle-less control, the challenges include achieving a competitive closed-loop bandwidth and achieving sufficient closed-loop positional accuracy in the presence of Coulomb friction and a non-collocated control structure.  These issues can be improved via nonlinear and model-based control techniques, but at some point provide a fundamental limitation on control performance.

Figure 1: Integration of vane motor with fixed displacement piston pump