Only control specific joints in the URDF file

Dear Team,

I am working on training a policy to control a robot in Isaac Gym. The robot description is in the form of a URDF file and the robot has several joints but I just want to control specific joints. I tried to mark the joints which have to remain fixed as “fixed” in the URDF file and the training works but I want to know if there is some way to fix the joints in the RL task (child class of VecTask for the robot) rather than the URDF file.

Any help will be much appreciated. Thanks.