Hello, I would like to define a 6-DOF free joint for a child body relative to its parent, with the intention of being able to toggle specific DOF later during runtime via mjModel's jnt_axis. This is to simulate the constraints that a threaded fastener would be subject to when attached to another body. On lines 38-39 of the attached .xml I have defined slide and hinge joints of a child body both with axis="1 1 1". However its parent also moves as shown in the attached image, so unfortunately those combined joints do not really behave as a free 6-DOF joint. Is there a better way to achieve what I'm trying to do? Apologies in advance if I'm missing something obvious, but I've been stuck on this for a while. Thanks!