Hip-Energized Hopping on Jerboa

This is a project I completed while in Kod*lab at UPenn, where we managed to stabilize movement for a tailed biped named Jerboa in the sagittal plane by using hip actuators to energize the system while using the tail to keep it steady.

Unfortunately, the work remains unpublished due to scope creep, but I am quite proud of my work in tuning the controllers with the goal of increasing stability and growing the basin of attraction. At the very least, you can see it working in the video below:

Previously for Jerboa, Kod*lab was using a tail-energized/hip-stabilized controller developed by Avik De of Ghost Robotics. In the interest of developing faster and more energetic gaits, we desired a hip-actuated controller. At first, we examined how to potentially use a Virtual Pivot Point with the notion that having forces for the duration of the stance phase intersect above the center of mass would provide stability. However, trying to get that sort of controller to work while also moving the tail to shift the center of mass was difficult to deploy in simulation, let alone hardware. So we turned to essentially PID (a Proportional-Integral Derivative controller): one controller for the tail to control the pitch, and another to control a unitless “energy.” (Side note: PID is one of my favorite control schemes ever because 8/10 times it works alone, and the other 2/10 times are probably using it in some form.)