Torsion Spring

[SteMuc91]

Intro

Hi!

I am a graduate research and I use MuJoCo for my research on robotic hands. I'm trying to simulate a 5 bar linkage and I need to add a torsion spring between 2 links that are adiacent but not connected through a joint. Is possible to add a spring in a connect/equality constraint?

Thank you very much for your help.

Best regards

My setup

MuJoCo 3.11, API Python

Confirmations

• I searched the latest documentation thoroughly before posting.
• I searched previous Issues and Discussions, I am certain this has not been raised before.

[v-r-a]

Hello, I am a MuJoCo user. I am unable to visualise your setup, but here is a suggestion:

You could use the mjcb_passive(m, d) callback and write the spring/damper passive law in it.

[SteMuc91]

Thank you very much for your reply. The problem is that I don't have a joint defined between the links but only a connect/equality constraint.

[v-r-a]

You can apply forces/torques wherever you wish on the bodies of interest using mj_applyFT().

For example, you wish to add a torsional spring, so compute the relative orientation between two bodies of interest, and apply equal and opposing torques via mjcb_passive. Specifying d->qfrc_passive as target in mj_applyFT will do the job.