Issues with revolute joint in Omniverse

Omniverse Apps USD Composer
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I was hoping someone could help me with a strange issue I’m encountering when adding joints. I am making a universal joint for a robot. The joint is made up of two revolute joints with the same origin but rotated 90 degrees from each other. If I add either of the revolute joints alone, they spin fine as expected. But after I add both, it ends up acting like a spring. It’s bizarre. It has me stumped. I can’t imagine any reason joints would behave this way. I can’t tell if I’m doing something wrong or if it’s a bug in the software. I used a screen capture to make a video – the forum won’t allow me to upload it so I put it on youtube and here’s the link: https://youtu.be/OujJKs_LpaQ

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Thanks, we will take a look and get back to you.

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Thanks Richard. Looking forward to any suggestions. If you need me to send the USD scene, let me know.

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Yes can you send me the usd file please

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Hi,
The problem is that the objects collide, when you create a joint between mesh1 and mesh3 and a joint between mesh3 and mesh4, this means mesh1 does not collider with mesh3 and that does not collide with mesh4, however mesh1 collides with mesh4.
So what you can do is to select the mesh1, right click Add->Physics->filtered pairs. Then there in property window add filtered pairs rel to mesh3 and mesh4.
Then the simulation would work, but probably not as you expect. Since you are using maximal joints, there is a tolerance that would not look good here. You want to have articulated joints here. So select the Rotation_Axis_Top prim and right click Add->Physics->Articulation root.
This should do the trick, should look like this then:

Regards,
Ales

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Awesome! It is working now. Thank you so much Ales & Richard. That would have taken me days or weeks to figure out-- if ever. Much appreciated!

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Fantastic !!

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@Richard3D @AlesBorovicka

Quick question. about this if I run into it again in the future…

  1. Is there a way to visualize or know when they’re interfering or colliding?
  2. If I would have simply changed the dimensions of the mesh so that they no longer interfere, would that also resolve the problem?
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  1. You are talking about collision detection. We do not have that built in, out of the box at the moment. There might be an extension for that
  2. Yes, just reducing the scale slightly, should give enough of a gap
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Thanks!

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Yes, you can visualize that. Going into Window->Simulation->Physics->Debug you enable the debug window for physics simulation.
There in PhysX Debug visualization part you can enable it and then enable for example collision shapes and contacts. Then when you press play you will see debug draw showing whats going on in PhysX SDK.

Regards,
Ales

1 Like
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