Prismatic joint oscillating - why?

[dan.sandberg]

bad_prismatic.usd (6.6 KB)
I’m having trouble getting a prismatic joint to work properly. I made a simple test case (attached) which has a tall block GroundedCuboid, which is fixed to the ground plane, and a smaller box SliderCuboid which is attached to GroundedCuboid with a prismatic joint.

I have tried really hard to align the joint local positions and rotations, and it looks fine as far as I can tell.

When I run the simulation, both cuboids bounce around erratically even though the bigger one is fixed to the ground plane.

Appreciate if someone can point out what detail I missed. Thanks!

[toni.sm]

Hi @dan.sandberg

@dan.sandberg

the bigger one is fixed to the ground plane

It seems to be this is the problem.
To fix it just leave one of the big cuboid fixed joint relationship empty:

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Visit the Rigid-Body Simulation Joints section for more details:

“It is also possible to connect objects to the static world coordinate frame if you leave one of the joint’s Body relationships empty (which is then implicitly relating to the world frame)”.

[dan.sandberg]

Wow, thanks so much, I just spent HOURS trying to figure that out!