Hello, all. My name is Meghaj Kabra, an undergraduate student at Purdue University. I am working using Isaac sim and Lab to train a custom quadrupedal robot. Right now I am struggling with getting joints right in Isaac sim for the quadrupeds leg. I am also on a timeline crunch and would be greatlful for your help. Issues are with revolute and prismatic joints. I am trying to use revolutes for creating motion on a fixed beam within the robot but the robot hinge or part does not stay on the beam. The goal is to rotate on a beam.
#Quadruped Joint issues
compact field
narrow jolt
Hello, all. My name is Meghaj Kabra, an undergraduate student at Purdue Universi...
You should provide more clarity/details
If possible files, what is happening and what you expect to happen
compact field
Hey @narrow jolt, hope you're doing well — thanks for reaching out to help!
We've been trying to get a single leg of our custom quadruped working in Isaac Sim 5.1.0 and have gone through several approaches, all with issues:
Onshape → URDF → Isaac Sim — joints didn't translate correctly
Onshape Importer (full assembly with mates) — parts exploded or joints misbehaved
Manual joint setup in Isaac Sim — imported STLs individually, added joints by hand. D6/revolute joints wouldn't constrain bodies (parts fell off even when all axes were locked). Root cause was likely missing articulation hierarchy and incorrect joint anchor positions.
Robot Wizard (current attempt) — grouped parts into Xforms as rigid body links (upper leg, lower leg, connector, motor hinge). Created 2 revolute + 1 cylindrical joint per leg. Current issues:
Revolute joints aren't staying on the pin or rotating freely — parts separate when sim starts
Cylindrical/prismatic joint is colliding with parts of the connector body
How the leg mechanism works: The motor spins a ballscrew mechanism (prismatic joint with the connector) to push down on the shin portion to rotate the shin around a pivot point (revolute joint) that is connected to the outer thigh. To prevent xy travel along the circle around the pivot point breaking the screw, there is a hinge mechanism (revolute joint) that the motor is attached to, which allows a little bit of x y angular travel in the motors motion which prevents that screw from breaking immediately.
Would love to schedule a call to screen-share and walk through the setup live — much easier to show than describe. Let me know what works for you. Thanks!
Here are the videos: https://drive.google.com/drive/folders/1y2RCFg-r5WLLhDzsuZeUJls5htlUn6mS?usp=sharing
crimson charm
Issue was solved
amber cloud
I am facing an issue with rotation axis misalignment. I’m importing a URDF exported from a CAD assembly. The CAD model is correctly constrained/modelled, and the joint positions/origins also appear to be placed correctly. However, after importing, the rotation axes seem misaligned and the joints rotate incorrectly. Any suggestions?
https://drive.google.com/file/d/165daq3OfXll0NBVTSG_Ccaxkd25TlblJ/view?usp=sharing
https://drive.google.com/file/d/1LP930L6i4fQZmdQCaInz6G5as1Zl0XvE/view?usp=sharing