I have created a new model of the ANYmal C robot with the adaptive feet described in this paper.
The instanceable asset can be downloaded here
anymal_c_softfoot_q.zip (4.2 MB)
In the folder there is the instanceable asset anymal_c_softfoot_q.usd and the anymal_c_softfoot_q_meshes.usd file containing all the meshes referenced by the instanceable asset.
These adaptive feet have a closed kinematics structure. Each foot is made up of 3 chains (right, middle and left), each made up of 9 links (5 inner and 4 outer). Each chain has 10 joints (counting also the ones that attach the entire chain to the front and back roll links).
Now, the simulation perfectly works if I leave the open kinematics structure, without attaching the last link of each chain to the corresponding back roll link. But I cannot use the feet in these way, because they would not have the adaptive feature they were designed for. So I need to close the kinematic chain.
Let’s take, for example, the left chain of the Left Front foot.
I add the 10th joint of the chain by adding a joint between the back roll link and the 9th link of the left chain, as shown in this picture
I exclude the joint from the articulation to make it work, I set the maximum joint velocity and upper/lower limits like all the other joints of the same type, keeping the joint friction equal to 0 as the joint is excluded from the articulation.
I press play and this is what happens
the robot basically disappear, it looks like it was wiped out.
While disabling this last added joint everything works (except the correct behaviour of the adaptive feet of course)
What should I do to make everything work correctly, closing the kinematics of all the chains of all the feet as needed?
Thanks a lot in advance for all your kind and precious replies.
If you could directly correct the usd file I shared and then share back the updated version I would be extremely happy and thankful. It would be greatly appreciated.