Simulating a closed-loop mechanism (Deta Robot)

Official Python bindings with a focus on reinforcement learning and robotics.
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Joined: Thu Apr 15, 2021 9:21 pm

Simulating a closed-loop mechanism (Deta Robot)

Post by nb789 »


I'm some-what new to Pybullet and I'm trying to simulate a Delta robot. As Pybullet will not accept closed-loops within an sdf file, I have left the sdf as an open-loop structure, with the aim of creating the spherical joints on the end-effector by using the createConstraint() function. I've been trying this for a while now but I haven't had much success; the constraint seems to initialise correctly but as I move the robot the links that are supposed to be constrained around a point move away from that point.

My question is, firstly, to make sure I understand how the function is meant to be implemented: My understanding is that you specify the position of the desired joint in the frame of the parent link (in its inertial frame) and of the child link (in its inertial frame) and then these specified points are made to be coincident (using the JOINT_POINT2POINT constraint); is this correct? I am quite sure that I've done this but it's still not working.

It's also very tricky to see if you've setup the constraints correctly because, as far as I'm aware, there is no way to display the constraint position on the GUI.

If anyone can let me know where I'm going wrong/general pointers how to go about solving this I will be very grateful!


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