System Identification for the Damiao actuator

[ParadoxRobotics]

Describe the feature you want

We are currently developing for the OpenArm a low-level controller for motion generation (GIK) using MINK.
We would like to get access to the system identification of the Damiao actuators (critical for sim2real).
Here are the parameters we need for our project :

• Kp, Kd gain
• motor armature
• motor joint friction (eg. friction loss in mujoco)
• motor damping value
• motor measured force range

We tried to find these values in the documentation and in the isaac sim repo, but we only found a global kp and a damping value.

Best regards,

Quentin.

[tokirobot]

Hi Quentin, thanks for reaching out and for the detailed question.

Below is the status of each parameter you listed and what we can currently provide on our side:

• Kp, Kd gains

Is there a specific reason why using the same Kp/Kd values for both the real hardware and simulation would not work on your side?
In our experience, using identical gains across real and simulated environments has not caused any issues.
So unless your simulation requires an intentionally different controller behavior, you should be able to reuse the real-world Kp/Kd values directly in MINK or MuJoCo.

• Motor armature

We do not have a dedicated armature-measurement tool in our repository.
However, the Damiao Tool provided by the manufacturer is capable of estimating this value.
You should be able to extract the armature information from there.

• Motor joint friction (e.g., MuJoCo “frictionloss”)

We have already completed an internal friction estimation pipeline, and plan to release it publicly in the near future.
Once it’s published, it should give you a friction model that aligns well with the Damiao actuators.

• Motor damping value

We currently do not explicitly model mechanical viscous damping.
Our approach is to keep the model simple for now and rely on friction terms instead.
So there is no standalone damping parameter available at the moment.

• Motor measured force range

You can refer to the official Damiao actuator catalog here:
https://github.com/dmBots/dmBot/blob/master/2024%E5%B9%B4-%E8%BE%BE%E5%A6%99%E7%A7%91%E6%8A%80-%E4%BA%A7%E5%93%81%E9%80%89%E5%9E%8B%E6%89%8B%E5%86%8C.pdf

It contains the torque/force limits for each model.

If you need any of these parameters in a specific format (e.g., MuJoCo XML, MINK config structure), feel free to let me know.
Toki

[ParadoxRobotics]

Hello Toki,

Thank you for your feedback !
It would be nice to have the current available parameters in a Mujoco XML and MINK config structure.
We would like to do admittance control and, in the long run, RL on the openArm, that's why I've asked for all these parameters. For me, the friction and the armature are critical.

Best regards
Quentin.

[tokirobot]

Hi Quentin,

The Mujoco XML file for OpenArm is available here: https://github.com/enactic/openarm_mujoco

This allows you to reference all the necessary simulation parameters directly.

We plan to release the parameter identification methodology soon to ensure high model fidelity.

Stay tuned for updates!

[xbkaishui]

Hello, how to do dynamic identification ? can you show some guide?

[ParadoxRobotics]

Hi @xbkaishui ,
Here are some actuator sys id framework i've used :

• https://github.com/Rhoban/bam
• https://github.com/based-robotics/mujoco-sysid
  It should be possible to adapt it to the openarm !