The generated spheres are not evenly distributed on the link using Lula Robot Description

[zhuceyonghu123]

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Isaac Sim Version

4.5.0
4.2.0
4.1.0
4.0.0
4.5.0
2023.1.1
2023.1.0-hotfix.1
Other (please specify):

Operating System

Ubuntu 22.04
Ubuntu 20.04
Windows 11
Windows 10
Other (please specify):

GPU Information

• Model: RTX 3070
• Driver Version: 570.86.15

Topic Description

Detailed Description

I’m using Lula Robot Description editor to generate the collision spheres for piper robot. After clicking “generate spheres”, the spheres are rather concentrated together, not evenly distributed along the link(first picture). I use ur robot to do the same thing, the generated spheres are well distribution(second picture).

piper’s urdf and mesh files are attached here:
piper.zip (2.9 MB)

There are some warnings in the terminal for both cases:
for Piper robot:

[Lula] 7722 triangles discarded from the 73166 triangles supplied in ‘triangles’. 65444 remaining in validated mesh
[Lula] 7722 triangles discarded from the 73166 triangles supplied in ‘triangles’. 65444 remaining in validated mesh

for Ur robot:

[Lula] 315 triangles discarded from the 17929 triangles supplied in ‘triangles’. 17614 remaining in validated mesh
[Lula] 315 triangles discarded from the 17929 triangles supplied in ‘triangles’. 17614 remaining in validated mesh
[Lula] 315 triangles discarded from the 17929 triangles supplied in ‘triangles’. 17614 remaining in validated mesh

What I’ve Tried

(Describe any troubleshooting steps you’ve already taken)
changing piper mesh file from STL to dae doesn’t work

[VickNV]

Thank you for providing detailed information and attaching your files. To better understand the issue with the uneven distribution of spheres on the Piper robot link, could you please upload a short video demonstrating the problem? A video showing the workflow and the resulting sphere distribution would help us diagnose the issue more effectively. Thank you!

[zhuceyonghu123]

Thanks for your reply. The video demonstration is here:

[VickNV]

Thank you for providing detailed information about your experience with the Lula Robot Description editor and for sharing your robot’s mesh and URDF files.

The uneven distribution of collision spheres is a known challenge that can occur with certain meshes. The Lula sphere generator may struggle with meshes that are non-watertight, have triangles with incorrect winding (normals pointing inward), contain excessive surface detail, or include degenerate triangles. The warning messages you see—about a high number of triangles being discarded—are a strong indication that your mesh has some of these issues.

For now, the most reliable solution is to hand-author the collision spheres for the problematic link. This process is straightforward and ensures good coverage.