DynamixelCommError. Mismatched baud rate

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1

Hello!

We’ve been running into an issue while homing the robot:

(base) sgupta-group@stretch-re2-2025:~$ stretch_robot_home.py 
For use with S T R E T C H (R) from Hello Robot Inc.
---------------------------------------------------------------------

[ERROR] [stretch_gripper]: DynamixelCommError. Mismatched baud rate. Expected 115200 but servo is set to -1.
[WARNING] [stretch_gripper]: DynamixelHelloXL430 Ping failed... stretch_gripper
DynamixelHelloXL430 Ping failed... stretch_gripper
Dnamixel Com error:

This occurred when we swapped out our end-effectors. We have also tried to run REx_dynamixel_id_scan.py:

(base) sgupta-group@stretch-re2-2025:~$ REx_dynamixel_id_scan.py /dev/hello-dynamixel-wrist
For use with S T R E T C H (R) from Hello Robot Inc.
---------------------------------------------------------------------

Scanning bus /dev/hello-dynamixel-wrist
Checking ID 0
Checking ID 1
Checking ID 2
Checking ID 3
Checking ID 4
Checking ID 5
Checking ID 6
Checking ID 7
Checking ID 8
Checking ID 9
Checking ID 10
Checking ID 11
Checking ID 12
Checking ID 13
Checking ID 14
Checking ID 15
Checking ID 16
Checking ID 17
Checking ID 18
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Checking ID 21
Checking ID 22
Checking ID 23
Checking ID 24
Found 0  servos on bus /dev/hello-dynamixel-wrist

To trouble-shoot, we’ve tried swapping out the end-effector with a brand new one, and also swapping out the cable that connects the robot to the end-effector with a brand new one, but still no luck.

In all cases, we observe that the red light on the end-effector flashes only once or twice when we connect the end-effector (see image below). Additionally, the yellow light on the end of the arm is blinking repeatedly. We also tried to change param.robot.tool in stretch_configuration_params.yaml according to https://docs.hello-robot.com/0.3/extending_stretch/changing_tools/ but didn’t work.

IMG_1398
IMG_13981920×2560 188 KB

Do you have any ideas to help us resolve this issue? We understand that this is limited information, so we’d be happy to get on a call to troubleshoot, if possible.

Thanks!

2

We were able to follow [Stretch2 Robot Arm PCB Issue: Gripper and Wrist Motors Not Detected - #2 by seung] for debugging, and believe we have the same issue.

Similar to the post, when bypassing the arm’s PCB and connecting the gripper directly to USB via U2D2, Dynamixel Wizard is able to detect the motors and also send torque commands.

It also seems like a part of our PCB is damaged, perhaps due to overheating (please see attached image).

Based on this, we believe the PCB in the robot’s arm may be malfunctioning. If the diagnosis seems correct, would it be possible to send us a replacement PCB?

Thank you!

IMG_5229.HEIC
IMG_5229.HEIC3024×4032 2.7 MB

3

Hi @Shaoting, thank you for the detailed post. Since the /dev/hello-dynamixel-wrist device is present on the USB bus, REx_dynamixel_id_scan.py reports that no servos are present, and the U2D2 board confirms that the servos are undamaged, I agree with your assessment that part of the “wacc” (wrist + accelerometer) PCB is damaged; likely the FTDI chip that converts the serial communication used by the Dxl bus to USB has burnt out. If you email support@hello-robot.com with your contact details and shipping address, we can send you a replacement PCB + instructions on how to perform the replacement. Thanks!

4

Thank you for the reply! I just sent an email to the support team :slight_smile: