A novel, miniature, low-mass vehicle has been created that is driven by piezoelectric stacks and a resonance structure. Preliminary tests on similar mechanisms that are used to transmit electrical power across the wall showed efficiencies of the order of 90%. The transmitted mechanical power, and signals through metallic walls using the direct and indirect piezoelectric effects in similar motors, is of the order of 50%. The transmitted power is generated inside the vehicle body, and the mechanism is applicable to any robotic system that may require an ambulation of locomotion mechanism such as a rover, a miniature vehicle, a crawler, or a flying device.

Cross-sectional view of the axis actuators and a wheel.
For this purpose, a piezoelectric stack, with a backing and stress bolt, generates ultrasonic vibrations that are transmitted through the vehicle walls. The stress wave excites a resonant structure that produces micro-motion at high frequency to create a rotary or linear actuation for the ambulation of the vehicle. This design avoids the need to use gears or bearings, as well as avoiding shafts or cabling through the wall. In addition to driving the actuators that move the wheels or robot legs, the transferred power can be used to activate sensors and other mechanisms. The elastic waves transmit mechanical power and signals through walls, and allow the performance of multiple electromechanical tasks. Tests have demonstrated using such vibrations to generate high torques at speeds as high as 900 RPM without the need for gears, bearings, or shafts. The motors are non-back-drivable, i.e., provide self-braking.

This innovation allows the driving of wheels or legs through the vehicle wall without perforating the structure. This can be critical in terrains that have harsh environments, such as Venus with its high temperature and pressure. Also, this design method can be used to drive a submarine in Titan’s lakes without concern for extremely low-temperature seals.

This work was done by Yoseph Bar-Cohen, Stewart Sherrit, and Mircea Badescu of Caltech for NASA’s Jet Propulsion Laboratory. NPO-49101

This Brief includes a Technical Support Package (TSP).
Document cover
Miniature, Multi-Functional, Self-Braking Vehicle

(reference NPO49101) is currently available for download from the TSP library.

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