Wheel speed in Isaac Sim velocity mode is inconsistent (starts and stops intermittently)

Omniverse Isaac Sim
,
1

I’m controlling the wheel of a robot in Isaac Sim using velocity mode. However, instead of maintaining a constant speed, the wheel rotates for a while and then stops intermittently. What could be causing this issue, and how can I ensure the wheel rotates at a constant speed without interruptions？

here is part of my code

sim_dt = sim.get_physics_dt()
    count = 0

    min_torso_joint_value = np.array([0, 0, 0, 0]) / 180.0 * np.pi *100
    steer_joint_value = np.array([0.9250663955407291, 0.7346690973447606, 0.6716847170203316]) /2
    zero_steer_joint_value = np.array([0.0, 0.0, 0.0])
    wheel_joint_value = np.array([0.2692006686470151, 0.32073197533142844, 0.2555014677061562])*135
    wheel_joint_velocity = wheel_joint_value

    target_velocity_wheel = torch.tensor(wheel_joint_velocity,dtype=torch.float32, device="cuda:0")
    robot.set_joint_velocity_target(target_velocity_wheel, joint_ids=wheel_motor_entity_cfg.joint_ids)

    while simulation_app.is_running():

        time = count * sim_dt *10

        torso_joint_position = min_torso_joint_value
        steer_joint_position = steer_joint_value

        target_position_torso = torch.tensor(torso_joint_position,dtype=torch.float32, device="cuda:0")
        target_position_steer = torch.tensor(steer_joint_position,dtype=torch.float32, device="cuda:0")


        robot.set_joint_position_target(target_position_torso, joint_ids=torso_entity_cfg.joint_ids)
        robot.set_joint_position_target(target_position_steer, joint_ids=steer_motor_entity_cfg.joint_ids)

        scene.write_data_to_sim()
        sim.step()
        scene.update(sim_dt)
        
        count += 1

2

wheel_velocity
wheel_velocity1000×500 94.8 KB

here is the result of wheel Velocity

3

In the video, I cannot tell if the wheel stops intermittently. Could you provide another clip?

Also, what if only the wheel joint is set and no other joints? Why is set_joint_velocity_target() called instead of set_joint_velocity_targets()?

4

Hey Vick,
Thanks for pointing that out! I’ve attached another clip for your reference. Upon closer observation, the wheel doesn’t completely stop, but its velocity fluctuates instead of remaining constant, which gives the impression of intermittent stops.
As for why I didn’t set other joints, it’s because my focus is solely on the movement of the wheel. I did try using set_joint_velocity_targets(), but it resulted in the following error:
AttributeError: ‘Articulation’ object has no attribute ‘set_joint_velocity_targets’. Did you mean: ‘set_joint_velocity_target’?

It seems that only the set_joint_velocity_target() method is available for the Articulation object in this context

I was aiming for the wheel to run at a fixed velocity, but it keeps intermittently accelerating and decelerating, as shown in the velocity graph above. Let me know if you have further suggestions or insights!