Joint_velocity targets never achieved and slowing down

Omniverse Isaac Sim
1

Hi, I am trying to velocity control the RidgebackFranka robot ( RidgebackFranka/ridgeback_franka.usd) in the nvcr.io/nvidia/isaac-sim:2022.1.1 docker image.

In particular I am sending the following:

a = ArticulationAction(joint_velocities=[0.2, 0., 0.], joint_indices=[0,1,2])
self._robots.apply_action(a)

The result is the following:

  • the robot over a few timesteps achieves a max. velocity of around 0.15
  • as it moves away from the origin, it then slows down. If I change the sign of the commands, it then accelerates again in the other direction, until it is further away from the origin and slows down again

So I have two questions:

  • why does it never achieve the actual target velocity but is always a bit slower
  • why does it then slow down, even though I continue to apply the same actions at each timestep?

Thank you for your help.

2

Turns out even if never setting position targets, the underlying controller will assume position targets of 0. So the solution is to simulatenously pass in the current position as a target