Closed kinematic chain simulation

[finnfi]

Hi,
We are currently trying to setup a simulation of a quadruped where each leg is designed like a five-bar-linkage system like this:

Is this closed chain kinematics supported by brax?

[btaba]

Hi @finnfi , we don't model closed kinematic chains in brax, but the way to do this in MuJoCo (or for the generalized backend) is to add a weld constraint at the paw. We don't have weld implemented in generalized right now
For spring/pbd, I would (maybe) expect such a system to sort of work (with a lot of tuning). But since we use the MJCF loader, you won't be able to create a system with a kinematic loop in Brax.
To sum it up, we'd need weld constraints implemented in Brax