Cryobotics: Extreme Cold Environment Testing of Strain Wave Gear Sets

In designing and building equipment to operate in extreme environments, including cryogenic temperature conditions, realistic performance testing is essential. The technology focus area, cryobotics, concerns robotic systems and rotating machinery that must operate at cryogenic temperatures in environments that include Earth, low Earth orbit, Mars, Moon, asteroids, Solar orbit, planetary orbit, or those encountered during travel among these destinations. Another given aspect is that cryogenic temperatures (below about 150 K) will be encountered and must, therefore, be dealt with early in the design process. The heat transmission effects of these temperatures, as well as the large temperature differences (AT) and quick changes in temperatures (thermal transients), and thermal cycling must be understood by testing in relevant environments. Knowing what factors are more relevant than others is key to being able to come up with an adequate experimental approach and build an appropriate test apparatus. The applications include mining equipment, spacecraft mechanisms, rotating machinery for superconducting power generation, cryofuel pumping systems, and so forth. Participating with science and industry partners in tribology research, dry lube technology, and material science in a collaborative way is a key facet of the focus area of cryobotics. This paper addresses the design, checkout, and testing of an extreme cold environment test chamber and the initial testing of Harmonic Drive strain wave gear sets and bulk metallic glass flexsplines in strain wave gear sets. This chamber was specifically designed for testing actuator subsystems, such as planetary gearboxes, strain wave gear sets, and full actuators in vacuum and at approximately 100 kelvin (K) and below. This chamber's capabilities include life testing while under specific loads, gear efficiency, gear wear, temperature monitoring, and other operational parameters.