Flywheel Test Bench for Actuators and Transmissions
Another objective of my doctorate was to develop actuators and transmissions that are capable of modulating their output mechanical impedance and human-scale power output. In order to evaluate the performance of such devices, a test bench was designed that would allow me to monitor the complete input and output states of the system under inertial loading, as shown in Figure 14. The test bench centers around an aluminum flywheel whose rotational inertia is roughly equal to an adult human’s shank. An encoder and a torque sensor measure the position and torque, respectively, at the flywheel. The actuator and transmission would be coupled to the torque sensor, corresponding to the brushed DC motor and flexible drive shaft shown in the figure. An additional encoder and torque sensor are located at the actuator such that the dynamical behavior of the transmission can be characterized.
Figure 14 - An instrumented flywheel test bench for characterizing actuator and transmission dynamics. Here, the flywheel is shown coupled to a brushed DC motor through a 3 meter flexible drive shaft. Encoders and custom torque sensors record the positions and torques, respectively, of the input from the actuator and the output at the flywheel. Custom signal conditioning circuits were designed for the torque sensors.
Custom torque sensors and signal conditioning circuits were developed for this application, which improved the system’s integration and modularity. The geometry of the torque sensors was optimized through finite element analysis deliver maximum linear strains under full load (17 Nm) while maintaining a factor of safety against yielding of 3 (Figure 15). A pair of dual grid shear strain gages were bonded to opposite sides of the sensor at the location shown and wired to form a full Wheatstone bridge. The signal conditioning circuit was developed on a breadboard before performing the PCB layout in Altium (Figure 16).
Figure 15 - Finite element analysis of the predicted strain in the flywheel torque sensor under full load. Dual grid shear strain gages were placed at the indicated location on opposite sides of the sensor.
Figure 16 - Blank signal conditioning PCB designed for the torque sensors used for the flywheel test bench.