Design, Analysis and Experimental Evaluation of a Gas-Fuel-Powered Actuator for Robotic Hoppers

Field robots often need to overcome obstacles multiple times their own size when exploring the environment. To address this need, we revisit a concept where a compact mechanical hopping actuator powered by gas-fuel was designed and tested. The idea is further refined, analyzed and realized in this reported study, characterized by a double-piston structure and a magnetic latch. Analysis is performed on the postcombustion dynamics to obtain the takeoff velocity of the actuator, which determines its jumping height. An experimental setup is constructed to test the design in indoor and outdoor environments. Laboratory (indoor) tests were carried out to obtain the takeoff parameters of the actuator, including the postcombustion pressure, takeoff velocity and force of the piston rod against the ground (ground reaction force). The expected high power output was observed, which justifies the actuation method for high payload applications. A takeoff velocity of 5.98 m/s was achieved at a relatively low charge pressure of propane and nitrous oxide, showing potential for higher performance at higher charge pressure to be investigated further. Finally, the outdoor experiment was performed and the actuator was demonstrated to jump 2.1 m high, with a payload of 2.43 kg and the body weight of 0.74 kg, which showed the high payload capability (~ 3.3 times body weight) of this actuator. Experiments also showed that higher postcombustion pressure and jumping height could be achieved by varying the mixing ratios of propane and nitrous oxide, peaking at the stoichiometric ratio for complete combustion. A metric defined as normalized payload was proposed as a means to compare the normalized performance of the hopping actuator against various robots with different means of power in the literature.