Custom URDF Vehicle Moving Backwards using ROS Differential Base

I am having an issue where the differential base setup using ROS in Isaac Sim cause my wheels to move backwards for a jeep-like vehicle. The back wheels are set to drive the system as well as steer but the issue has been bothering me for so long since i have no clue how to fix it. I have set my Axis to Y for all wheels and set them to use “Acceleration” in the Angular section. It also seems that my front wheels are stiff as a brick and make my vehicle jump up and down. I have included a video of the problem I’m facing. Is there a step I am missing to configure my vehicle?

I have attached a youtube link showing my issue:

I’m still having this issue.

I assume all of your wheel joints are under your base_link? In your front wheels’ joint setup, try checking the box “Exclude from Articulation” in the Property tab under the “Revolute Joint” section. Do the front wheels now spin freely when the jeep moves? If not, also try deleting the joint’s drive, so that there’s no actuation involved for those joints, only a mechanical connection.

The driving backwards may be related to a bug we are trying to fix.

how to get imported model to move at all? without ros ? is there a simple way to do so?

If you are writing scripts, dynamic control extension have examples on how to move the joints. If you just want to see if the joints could move or not, you can open the joint’s property and set a target velocity or target position under joint drive, and then press “play”.

In case of the jeep, you should be able to select the two rear wheel joints and set a target velocity and then press play (make sure those joints are have high damping and zero in stiffness for velocity control). Your front wheels should not even have a drive component since you shouldn’t technically be able to actuate it.

Hello Qwan,

Thank you for your response. I have done as you said to exclude the front wheels from articulation, but it made no difference in changing the direction in which the vehicle moves. It still moves backwards and jumps up and down. The front wheels also do not spin freely and are stiff as a rock. I have also disabled the robot’s front wheel joints and it caused the front wheels to ragdoll and the vehicle to flip backwards and just move around freely on its axis as if it were rotating on an axle. I am not sure where to go from here and any advice would be appreciated

Update: I was able to get the front wheels to move by removing the drive component instead of the joint component so its a little better in movement albeit not perfect since it moves back and forth a lot. However, the vehicle is still moving backwards and it struggles to turn left or right.

Here is the result of the error I got:


right, don’t disable the joint, only the remove the drive component. glad you got that working.

The moving backwards is a bug that should be fixed in our next release. For now, you may need to either flip the rotation axis, or temporarily give it a negative velocity.

The first thing I would try in terms of the turning problem is tuning the wheel’s friction. Please refer to our documentation for the instructions on that. Also maybe play with the weight of your vehicle to affect friction as well.