February 2022 update

A project log for Upkie wheeled biped robots

Wheeled biped robots that can balance, go around and more. Upkies are fully open source, both hardware and software.

upkie-zeroUpkie Zero 06/05/2022 at 11:100 Comments

Here comes a shot of the robot in its natural habitat: the living room!

The main improvement in this update lies in the locomotion software, which performs smoother motions and allows the robot to crouch down further.

There is also a hack, documented in the code as the non-minimum phase trick, to improve transitions from standing to driving with the simple PID balancer. Some pointers to dig further: this hack helps handle the non-minimum phase nature of balancing systems (the fact that to go one way one first needs to go "a little" the other way, like counter-steering in bikes) without going for full model predictive control.

The small wheels (OD: 100 mm) on Upkie are nice because they are sleek, which fits well the assumption made by the PID balancer that controls the velocity of the contact points with the ground, unfortunately they are also a bit small which doesn't fit the ankle design so well. That, rather than knee torques, is actually what limits how much the robot can crouch before it starts scratching the hell out of the floor (^_^)