Real-Time Physics Simulation Forum

Re: Programmatically create a multi-body chain

2018-10-05T01:04:06+00:00

We didn't expose spherical joints in PyBullet yet, since none of our robots have spherical joints. You can use multiple revolute joints though.

>> Is there a way to specify the joint position w.r.t. the parent body,

Yes. I would suggest first learning a bit more about URDF, that gives a better idea.
The 'linkPositions' and 'linkOrientations' allows to express the link/joint frame. In addition, you can express the inertial frame of each link, and the visual shape/collision shape have their own local frames too.

The UrdfEditor can also help, see https://github.com/bulletphysics/bullet ... fEditor.py
(you can load a URDF, then it can programmatically re-create a similar multibody as the URDF)

Statistics: Posted by Erwin Coumans — Fri Oct 05, 2018 1:04 am

Re: Programmatically create a multi-body chain

2018-09-28T17:29:25+00:00

Not sure I understand it perfectly but I maybe my example video: https://www.youtube.com/watch?v=F-Pj9AV6wfo can help you. The sourcecode is found at https://github.com/richardbloemenkamp/R ... obotdog.py. Basically I use extra small objects as joint elements. There may be better ways though.

Statistics: Posted by richardbloemenkamp — Fri Sep 28, 2018 5:29 pm

Programmatically create a multi-body chain

2018-08-21T13:09:51+00:00

I am trying to create a multibody chain in pybullet similar to the C++ example in examples/MultiBody/SerialChains.{cpp|h}. So far the plan is to use

Code:

mID = createMultibody(...)

for this purpose. So far, the following problems occured:

spherical joints do not seem to work. As far as I was able to follow the code, the problem lies in class examples/SharedMemory/PhysicsServerCommandProcessor which creates a multibody object with a ProgrammaticUrdfInterface instance. Is there a possibility to bypass the loading of an URDF file on multibody creation to directly create a btMultiBody object? Or would this need a rewriting of the pybullet/C API?
even when using rotary joints (to create a 2D representation) I was not able to create the joints between the ends of two links. Instead, the joint was always rotating around the center of mass of the parent link. Is there a way to specify the joint position w.r.t. the parent body, which I missed? I only found the linkPositions parameter specifying the position from joint to child body.

Best regards
Chris

Statistics: Posted by chhinze — Tue Aug 21, 2018 1:09 pm