Chain of bodies that looks like a loop, is this possible?

[DarioUrbina]

I want to join a child link (i.e. Link #10), to the base link (i.e. link #-1). This is generating discrepancies when trying to run the simulation.

Since I cannot accomplish this with declared joints in my .urdf files, I have opted to restrict the motion of a body with a artificial joint (I am relying on collisions to do so). This is apparently a good solution. But when working with very complex bodies the collisions are not respected and the models behaves like in a chaotic way.

Here you can see my code: Pendulum_exercise/Inverted_pendulum_tendon_actuation.py

[erwincoumans]

You can create a fixed constraint (or point-to-point constraint etc) to create loops, using pybullet.createConstraint.
See for example: https://github.com/bulletphysics/bullet3/blob/master/examples/pybullet/examples/constraint.py
You can pass in a parent body unique id, link index and child body unique, link index. For a loop the parent and child body unique id can be the same.

We use this for example in the Minitaur quadruped robot to create a loop for each leg (5-bar linkage):
https://github.com/bulletphysics/bullet3/blob/master/examples/pybullet/gym/pybullet_envs/minitaur/envs/minitaur.py#L378

There are no links to your code (Pendulum_exercise/Inverted_pendulum_tendon_actuation.py), can you attach them as zipfile?

[DarioUrbina]

Thank you for the reply,

In the zip file you can find the files, the first to the Python code, the second to the URDF code:

I just updated the file to the version you should see, the file you saw a minute ago is not the right one, please open this one:

Inverted_pendulum_tendon_actuation.zip

You will see that even though the model looks right, when moving the pulley (wheels), it can enter into a chaotic behavior.