AX-12As stopped working

My friend and I have been having trouble setting up some AX-12A servo motors. I finally got one to work a week or so ago, but we are no longer able to communicate with them.


DYNAMIXEL Actuator: AX-12A
Controller: OpenRB-150 (originally tested with an ESP-32, Arduino Uno, and OpenCM9.0.4)
PC: x64 Windows 10 Laptop, also tested with a Macbook (model/architecture unknown)
Power Supply: Bench power supply @11.1VDC, 12VDC, also tested with 11.1VDC LiPo batteries

Background & Initial Issue Description

We inherited a project from some older members of our college robotics club without any documentation regarding the state of the electrical and motor control subsystems. We were going to use my Windows laptop and an ESP32 or Arduino Uno to control the Dynamixel AX-12A servos, but we were unable to get the servos to work and I realized that the serial standards were not directly compatible. We knew that a OpenCM9.0.4 board had been used in the past, I tried one that had been lying around, but I had trouble installing the drivers and I was unable to get my laptop to recognize it. We then bought the OpenRB-150, as it is affordable and seems to be newer/better supported.

Current Issue Description

I was able to connect to and control the servos from Dynamixel Wizard 2.0 and then I disabled the test setup at the end of the meeting. When I tried to test it again a week later, it wouldn’t work. My laptop could communicate with the OpenRB-150, but both Dynamixel Wizard 2.0 and the Arduino could not see the AX-12A. Dynamixel Wizard could not detect any of our other servos either. Any help would be greatly appreciated.

Working Setup:


Broken Setup:

Power Supply:

Motor and connections:




Software (Dynamixel Wizard 2.0):


  • I haven’t tried reinstalling the software yet. Edit: The the official Dynamixel2Arduiono scan_dynamixel code cannot find the servos either.
  • I haven’t called Robotis support yet.
  • I just realized that in the photo of the working test, the OpenRB-150 red is lit, indicating that the motors are powered while it is not in the broken test’s photo. I’m not sure if that is the issue though because I remember checking and the AX-12A was receiving 12VDC. Edit: This does not appear to be the issue.

The simplest suggestion that might resolve this issue is to reupload the DYNAMIXEL2USB example code to the OpenRB and perform a firmware reset on your DYNAMIXELs. This should take care of any possible misconfiguration or firmware corruption that might have caused the issue.

Thank you for your response. I could not find anything labeled as “DYNAMIXEL2USB example code”, but I tried uploading the official Dynamixel2Arduiono scan_dynamixel code. Unfortunately, the program reported that it couldn’t find the motor and Dynamixal Wizard 2.0 is still unable to locate it as well.

PS Sorry for the delay replied, we only meet about once a week and we approaching the end of the quarter.

Edit- Additional observations:

  • My laptop can communicate with the OpenRB-150
  • When the OpenRB-150 is providing power to the servos, hot-plugging one in will cause the red status light on the servos to briefly turn on.
  • I found several more servos to try and neither worked.

The USB to DYNAMIXEL example sketch must be uploaded to the OpenRB-150 for use with DYNAMIXEL Wizard configuration software.

If you reupload that sketch, then following the firmware reset process in DYNAMIXEL Wizard will allow us to determine if this is a simple firmware corruption issue, or if your AX servos may require RMA repairs.