Revolute joint not working; how to fix this and other mesh / collider issues

Hi everyone! I am creating an animation for this “cherry picker” machine:

Since I am new to Omniverse / Isaac Sim, to get started I am first modeling the revolute joint between the base of the machine and the first “rotator” link that is attached to it. However, I have not been able to successfully create a simple rotating motion, as this video shows:

Thus I would like to ask you:

  • Do you think that this could be caused by the parts colliding with each other? Please notice that each surface in this model is an independent mesh (i.e., the base of the machine is not a single mesh, but a lot of individual meshes instead). Similarly, doing changes to the collider properties could be a solution? (For example, changing their approximation from “Convex Hull” to “None”).

  • In order to simplify the model, how can I merge all the meshes while preserving their colors/materials? When I run the “Mesh Merge Tool”, surfaces of different colors all become gray in the resulting merged mesh. Or in case this is not possible, is there a quick way for choosing all the colliders and editing them in bulk? I tried using filters or the search bar, to no avail unfortunately.

  • How can I make the base of the machine become fixed to the ground, so that the only part that rotates is the rotator link? I tried adding an “Articulation Root” and a “Fixed Joint” to the base of the machine, but this didn’t work.

Here you can download the .USD file that I am using: Microsoft OneDrive

In advance, thanks for your support!

you dont need the articulation here.
Anyway to answer your questions:

  1. For the collisions if you dont have the articulation the rigid bodies connected by the joint dont collide with each other by default, if you use articulation you can uncheck self collision on articulation to disable collisions.

  2. Convex approximation is fine you should use it

  3. The whole object moves significantly because you added a very strong drive that generates large force, remove the position part, you can have a velocity drive like this for example:

  4. You dont need the fixed joint I think, you can remove it should be not needed if the drive is fixed

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Just to clarify, I did not remove the fixed joint because it prevents a “falling movement” from occuring, since the machine’s “feet” are a little bit elevated and avoid touching the ground plane by a few millimeters.

Regarding my second question, do you have any idea of how I could simplify the model by merging the meshes while preserving the colors, or also how I can edit in bulk all of the colliders at once?

Thank you very much @AlesBorovicka , your quick reply solved my main issues!

You should not need to merge those meshes in general. You could use eventually subsets for the different colors, but I dont think there is a straight forward tool for that.
Anyhow you can bulk edit the collisions, in the stage window, there is a filter on the top right side. Filter for collisions, then you can bulk change the collision approximation, but in general for your dynamic objects convex approximation or eventually bounding box are the best.
In the next IsaacSim release, there will be a feature called CollisionMergedMeshes, where you can select more mesh prims and they will get under the hood merged into one mesh that will serve as the collision representation, but right now I would stick with the convexes.


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