Kp, torque and damping ratio

[ducmngx]

Intro

Hi!

I am a Ph.D. student at George Mason University, I use MuJoCo for my research on mobile manipulation and robot safety.

My setup

MuJoCo with Python for Ubuntu 20.04

My question

As I played around with these numbers, I realized that If I set kp to 0 for actuator and damping to 0 for the same joint, the joint would "fail" and my robot arm would drop to the floor due to gravity. This is the desired behavior I want for my failure injection project. However, I can't seem to find a way to trigger this during execution. They seem to be set before and not to be changed. I wonder if my assumption is true and if there is any other way to mimic this behavior.

Minimal model and/or code that explain my question

If you encountered the issue in a complex model, please simplify it as much as possible (while still reproducing the issue).

Model:

minimal XML

<mujoco>
  <worldbody>
    <light pos="0 0 1"/>
    <geom type="sphere" size="1" rgba="1 0 0 1"/>
  </worldbody>
</mujoco>

Code:

import mujoco
import mediapy as media
model = mujoco.MjModel.from_xml_string(xml)
data = mujoco.MjData(model)

with mujoco.Renderer(model) as renderer:
  mujoco.mj_forward(model, data)
  renderer.update_scene(data)

  media.show_image(renderer.render())

Confirmations

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

[ducmngx]

I am using a Fetch mobile manipulator model and I want the arm to drop suddenly to mimic hardware failure