My team created a one-legged vertical hopping robot. The project analyzed the effect of spring stiffness on jumping efficiency (a measure of energy consumption similar to cost of transport).
This project was created as part of the MIT course 2.74, Bio-Inspired Robotics, which I took this fall. The course is taught by Sangbae Kim, creator of the famous MIT Cheetah robot.
We independently varied two stiffnesses: the passive ankle stiffness adjusted via a rubber band on the foot, and the active hip stiffness enforced by the motor control.
My role was to work on the control and optimization of the robot, using simulation to find the stiffness combination that would theoretically maximize jumping efficiency. The control scheme is divided into a jumping period where a torque impulse is applied, and a landing period where an effective stiffness is enforced actively with impedance control. The magnitude of torque impulse is computed to ensure that the robot reaches the same height for all stiffnesses, to standardize the efficiency comparisons. Simulation was done in matlab, using Lagrangian dynamics and an ODE solver.
We performed physical testing, and got results that vaguely resembled simulation. Discrepancies could be due to any of several factors not modeled in simulation: slippage of the foot on the table while landing, backlash / deadband in the leg joints, inertia of the motor (amplified by the gear ratio), and spring nonlinearity of the rubber band.
Shout-out to my other group members: Amro (simulation), Christian (mechanical design), and Skye (electronics and testing).
Comments