AX-12A Position mode dont work but velocity does.

[B-Harakat]

ISSUE TEMPLATE ver. 1.0.0

Before you open issue, please refer to ROBOTIS e-Manual

1. How to setup? (ex, U2D2, OpenCR,...)
   Im using a dynamixel shield paired with Arduino MEGA

2. Which Dynamixel have you used? and how many? (Please describe below format to all connected Dynamixels)

   • Model Name
     AX-12A

   • ID
     2

   • Baud Rate of Dynamixels
     1000000

   • Protocol Version
     1.0

3. Write down the commands you used in order

The position mode example file, both from the dynamixel2Arduino library and the Dynamixel Shield library

4. Copy and Paste your error message on terminal

SUMMARY
========

PARAMETERS
 * /baud_rate: 57600
 * /device_name: /dev/ttyUSB0
 * /ping: False
 * /ping_id: 1
 * /rosdistro: kinetic
 * /rosversion: 1.12.13
 * /scan_range: 10

NODES
  /
    single_dynamixel_controller (dynamixel_workbench_single_manager/single_dynamixel_controller)
    single_dynamixel_monitor (dynamixel_workbench_single_manager/single_dynamixel_monitor)

auto-starting new master
process[master]: started with pid [8594]
ROS_MASTER_URI=http://192.168.1.3:11311

setting /run_id to de3bd71e-728e-11e8-9f66-d8cb8af3d300
process[rosout-1]: started with pid [8607]
started core service [/rosout]
process[single_dynamixel_monitor-2]: started with pid [8618]
process[single_dynamixel_controller-3]: started with pid [8626]
[PortHandlerLinux::SetupPort] Error opening serial port!
================================================================================REQUIRED process [single_dynamixel_monitor-2] has died!
process has died [pid 8618, exit code -11, cmd /home/darby/catkin_ws/devel/lib/dynamixel_workbench_single_manager/single_dynamixel_monitor __name:=single_dynamixel_monitor __log:=/home/darby/.ros/log/de3bd71e-728e-11e8-9f66-d8cb8af3d300/single_dynamixel_monitor-2.log].
log file: /home/darby/.ros/log/de3bd71e-728e-11e8-9f66-d8cb8af3d300/single_dynamixel_monitor-2*.log
Initiating shutdown!
================================================================================
[single_dynamixel_controller-3] killing on exit
[single_dynamixel_monitor-2] killing on exit
[rosout-1] killing on exit
[master] killing on exit
shutting down processing monitor...
... shutting down processing monitor complete

5. Please, describe detailedly what difficulty you are in

I am trying to use my dynamixel motors as a servo, they used to work fine but I left them in the closet for a few month because I was busy with uni. Now that I've got more time I picked them up again for some side projects, however, the position control no longer works. However, if I were to upload the "velocity mode" example files they work fine.

When running the "position mode" script, I can hear periodic "clicking" sounds from inside the motor that matches with the timing of the script, but the motor itself is not moving. It is almost as if the motor is stalled by something even if there is no load. I've tried with multiple motors (all AX-12A) but the issue persist, so I do not think its a motor problem. I am confident my baudrate and protocol versions are correct since the example files worked a few month ago, I struggle to understand what changed to cause this issue.

I am using dynamixel2arduino 6.3 and DynamixelShield 2.0

[yun-goon]

Hi @B-Harakat
Sorry for the delayed response.

The "clicking" sound often indicates potential hardware issues. Here are some common causes and solutions:

Mechanical Blockage or Overload

Cause: Excessive load or physical blockage prevents servo movement.
Solution: Remove all attached loads and test the servo. Check and reset the Torque Limit.
Internal Gear Damage

Cause: Worn-out or misaligned internal gears.
Solution: Open the servo and inspect the gears. Replace them if damaged.
Power Supply Issue

Cause: Insufficient or unstable power supply.
Solution: Ensure a stable power source of 9V–12V. Use a high-quality adapter or fully charged battery.
Firmware Update

Cause: Older firmware may have bugs or compatibility issues.
Solution: Update the firmware of your AX-12A to the latest version using DYNAMIXEL Wizard 2.0.
Please try these steps and let us know the results!