Looking for Proper Way to Acctuate Tendon

[benjaminswervey]

Intro

Hi!

I am a graduate student at Ohio State, I use MuJoCo for my research on Compliant Mechanism Design.

My setup

I am using Mujoco 3.3.0 on Ubuntu 22.04

My question

I am trying to simulate a tendon driven mechanism in mujoco and am getting conflicting results based on how I actuate the mechanism. The first method I tried attaching the base of the tendon to a body and controlled the position of the body using a motor actuator and a slide joint. That resulted in the following geometry

Next, I tried attaching the base of the tendon to a weight and use gravity to pull the tendon. (this was inspired by the tendon demo I found on the XML reference page). This method resulted in this geometry, where you can see the basal joints bend more than the less basal joints.

As far as I can tell, both of these methods should result in a force being applied to tendon in the same way. The gravity method (where the joints bend at different rates) seems to match our physical models best but it seems impractical to control more complex mechanisms with gravity. Is there any reason why these should be different? And is there a better way to control the tendon accurately?

Minimal model and/or code that explain my question

    </body>
    </body>
</body>

Confirmations

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

[benjaminswervey]

Nevermind, when using the gravity method I forgot to account for the fact that increases in gravity would also effect the finger segments