build with mjcf

[kassasin]

Hello！I am now very troubled by the parallel mechanical structure. Placo can only process urdf now. If I want to solve the robot with parallel mechanical structure, I need to add qp constraints manually. Can we build the model directly from mjcf (I noticed that pinocchio supports building constrained model from mjcf) and build a complete qp problem based on it?

[Gregwar]

Hello,

I haven't investigated this, but it would definitely be interesting indeed.
If I understand properly:

• pinocchio parse the XML for equality constraints
• currently, only connect is supported, see: https://github.com/stack-of-tasks/pinocchio/blob/devel/src/parsers/mjcf/mjcf-graph.cpp#L817 other constraints could be considered, in particular weld
• the output could be retrieved in the contact model, and indeed be used to automate the creation of kinematics constraints

Maybe supporting MJCF as input format for the PlaCo wrapper would be a first step

I can't work on that right now, but will definitely consider this. We are using more and more MuJoCo as simulator, and having the same model loaded in PlaCo is really something that would be interresting

[kassasin]

Hello,

I haven't investigated this, but it would definitely be interesting indeed.
If I understand properly:

• pinocchio parse the XML for equality constraints
• currently, only connect is supported, see: https://github.com/stack-of-tasks/pinocchio/blob/devel/src/parsers/mjcf/mjcf-graph.cpp#L817 other constraints could be considered, in particular weld
• the output could be retrieved in the contact model, and indeed be used to automate the creation of kinematics constraints

Maybe supporting MJCF as input format for the PlaCo wrapper would be a first step

I can't work on that right now, but will definitely consider this. We are using more and more MuJoCo as simulator, and having the same model loaded in PlaCo is really something that would be interresting

Yes! Maybe I can do some work on this.

[Gregwar]

Constraints are still not loaded, but MJCF models can now be used by passing flag to robot wrapper:
https://placo.readthedocs.io/en/latest/basics/load_robots.html#using-direct-urdf-contents

(Pushed in the latest released wheel v0.9.15)