Dynamic Template-Based Behaviors in 3D Space

The templates and anchors hypothesis has been used to generate many dynamic behaviors for quadrupedal robots using the parallel or sequential composition of simple planar dynamical systems. Historically, the kinematics of the robots have limited the amount of motion outside of the sagittal plane. As it becomes more common for quadrupeds to be able to exert forces in three dimensions, anchoring these planar templates presents additional challenges.

To accomplish this, Tim has developed a novel anchoring that stabilizes the robot’s out-of-plane degrees of freedom without interfering with the sagittal plane templates and implemented it on a Ghost Robotics Spirit 40. This anchoring enabled Spirit to perform dynamic behaviors that were developed for Minitaur, using Spirit’s additional degrees of freedom to reject out-of-plane disturbances. In addition to demonstrating that defining behaviors as compositions of planar templates yields useful dynamic behaviors on modern quadrupeds, these results demonstrate that behaviors defined in this way are platform-independent. Since both Minitaur and Spirit use the same compositions of templates, they are performing the same behaviors.

Current work endeavors to demonstrate stronger stability guarantees for the controller, aiming to demonstrate its ability to stabilize any planar template. Additionally, Tim is exploring applications of the controller beyond the sagittal plane, using it to stabilize motions in three dimensions. Ultimately, the goal is to develop modular behaviors that can be composed by a motion planner to autonomously plan dynamic motions through 3D space.


Timothy Greco, Daniel E. Koditschek



AFRL grant FA865015D1845 (subcontract 669737-1)