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

[WarsellusMallace]

Hi,

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:
https://youtu.be/iLiX88-3Fqs

Another video of motion without sliding (note that this video is sped up):
https://youtu.be/IBej4-MCf1E


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):
https://youtu.be/ZUqKuK69fik

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: https://github.com/unitreerobotics/aliengo_pybullet
Add my attached file to the directory and change its extension from .txt to .py. Then run:

Code: Select all

python aliengo_modified.py

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

Thanks