Detailed internal structure of the AX-12A motors

Use the following template to help create your post:

  1. What model of servo are you using?
    AX-12A servo motor
  2. Describe your control environment. This includes the controller or interface, and any power source.
    I intend to control the servo motor using a Raspberry Pi 4b through MATLAB with the aid of the Raspberry PI support package.
  3. Specify the operating mode for applicable models, and any firmware settings you are using.
    I’m going to use the servo in joint mode.
  4. Include pictures if possible.
  5. Include a full description of the issue.
    I’m going to give you the context of the work that I’m doing to better understand my issue. I’m studying the dynamic modelling and control of a 7 DOF robot manipulator for the purpose of visual servoing using an eye-in-hand configuration. I’m also willing to design a controller capable of compensating the dynamics of the robot arm for better control quality. My precise problem is that I require detailed information concerning the internal structure of the AX-12A motors showing the rotor structure and the gearbox precise location. These info are usually important in the case of high geared motors because the rotor apparent inertia might dominate the link inertia (to my knowledge, the AX-12A motors have a high gear ratio of 254:1 which might affect the dynamics. For more info on this matter I refer the interested reader to the book Modern Robotics by Park Lynch, Chapter 8 in which this idea is discussed in detail). Precisely, my questions are:
  1. Is there a detailed drawing of the motor taking into account the rotor of the DC motor and the gearbox (if it exists, is there a CAD model describing these details) ?? The exact info that I need are the inertia matrix of the rotor and the locations of the axis of rotation and the rotor inside the motor (these axes may not be aligned because of the gearing and motion transmission).
  2. Is there any way to access or alter the built-in controller parameters of the AX-12A motors ??
    Any help or discussion is really appreciated.

Thank you very much for your effort and attention :blush:


  1. No. ROBOTIS may not open Dynamic parameters and Gear information on AX series.

  2. Unfortunately, the built-in controller is designed in its firmware. Therefore, it might not be possible to edit the internal controller. If needed, DYNAMIXEL-X series has PWM Operating Mode which dosen’t implement the built-in controller (P.I.D and Feedfoward). Therefore, you can add your loop-controller outside if I am right.

  • Additionally, If you need Intertia information, you should probaly want to use XM/XH series as intertia inforamtion can be available at Download Center

Thank you very much for your response … I got exactly what I needed and I shall consider using the XM/XH series since as you mentioned, the inertia information are available.
Again, thanks alot for your thorough response.

1 Like

No worries,

For your reference,
ROBOTIS developed OpenManipulator-X which might be the similar application that you are planing to build (ROS Platform, Kinetic mainly, All packages are open-sourced)–DYNAMIXEL XM430 series are used. For Eye-in-Hand config, see 8.Perception

Enjoy your build, and showcase your application later at the community which will inspire other users :slight_smile: