Rollers — skating on velocity commands

Mjlab-Velocity-Flat-MicroDuck-Rollers

Velocity tracking with passive wheels fitted under the feet. It is roller mode’s main task, the counterpart of Velocity in walk mode.

What passive wheels mean

The wheels are not driven. The robot does not move by turning them; it pushes itself along with its legs the way a person on roller skates does, and the wheels only reduce friction.

So this is a fundamentally different mode of locomotion. It has to be trained separately — you cannot tune your way there from a walking policy.

The controls change too

On a robot configured as roller (mode = "roller"), the sticks take the roller shaping automatically: asymmetric push and brake, no strafe. A becomes the crouch rather than the ground pick.

Switching modes needs no restart

Fit or remove the wheels, then hold D-pad up for three seconds: the robot quacks once for walking or twice for roller, returns to its home pose, loads that mode’s policies there, and drives again. Torque on throughout.