Muscle for artificial muscle application

[martantoine]

Hi,

I'm a student and I'm trying to use MuJoCo for robots actuated with artificial muscles.

I'm looking for some help with the muscle actuator, I am not sure about how I could model McKibben actuator (pneumatic actuator).
The system has fixed, yet unknown tendon length. It also have a fixed muscle length, which I would like to specify.

From my understanding of Mujoco muscle actuator, the tendon length and muscle length are pretty much the same, except if I specify a gear value different from 1.
According to vittorione94 post here, if I set gear to 2, I should get the muscle length to be twice as large as the tendon length

However, in my case it would be much better if I could explicitly specify the muscle length. Is this possible in Mujoco ?

Another question to clear a confusion I have about the range (and not lengthrange) variable. Is this specifying soft constraints on the muscle length strain. If so, then by default the muscle length can undergo a strain of -25% and +5% right ?

Finally, why is scale equals by default to 200 and not something like 1 ?

I don't think that a model would make this issue easier to understand, but just in case here is the whole model in the description

Thank you for your help