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Unrealistic robot sliding motion caused by positionGains, velocityGains, action repeat

Posted: Tue Jan 12, 2021 5:39 pm
by WarsellusMallace

I have the Aliengo quadruped robot (sold by Unitree Robotics) in simulation executing a simple joint trajectory that involves squatting and pivoting in place (without lifting feet).

Video of motion in real time, no sliding:

Another video of motion without sliding (note that this video is sped up):

However, if I increase the "positionGains" AND "velocityGains" for "p.setJointMotorControlArray()" AND repeat the same action for two or more simulation time steps, the robot translates along the ground in an unrealistic manner:

Video of sliding behavior (again, sped up):

Does anyone have any insight on why this is happening? Perhaps it has something to do with this statement in the PyBullet quickstart guide:
Note: the actual implementation of the joint motor controller is as a constraint for POSITION_CONTROL and VELOCITY_CONTROL . . .
Code for replication:

Clone the repo from Unitree robotics here:
Add my attached file to the directory and change its extension from .txt to .py. Then run:

Code: Select all

By modifying the constants at the top of the "" script, you can change the sliding behavior.