FastSyncRead Rx Fail [Dxl Size : 16] [Error code : -3002] & Communication Fail --> SYNC_READ_FAIL

[InguChoi]

Hello, I’m trying to control multiple Dynamixels with dynamixel_hardware_interface.
My purpose is to control the LEAP robot hand which includes XC330-M288-T actuators (total 16 motors).

When I launch my package, I get the following result:

• print.txt
• Screenshot:
  

I already checked the following related issues:

• USB latency issue
• Home position issue #66
• Home position issue #333

I tried the suggested solutions (USB latency setting, home position configuration), but the error still occurs.

My questions are:

1. Is this problem related to USB latency or configuration of the dynamixel_hardware_interface parameters?
2. Are there recommended settings (baudrate, sync read/write options, etc.) when controlling 16 Dynamixels simultaneously?

Best regards,

[InguChoi]

I can control the Dynamixels using ros2 action send_goal successfully:

However, when I activate ros2_control_node, the following error message still appears:

[Woojin-Crive]

Hi @InguChoi !

Can you try to set the return delay time to 0 of all dynamixels?

https://github.com/ROBOTIS-GIT/dynamixel_hardware_interface_demos

Example ros2_control.xacro files can be access through that repo.

Thanks!

[Woojin-Crive]

And can you let us know the baudrate you are using and if it's configured with all dynamixels daisy chained?

[InguChoi]

@Woojin-Crive Thank you for reply!

1. Return Delay Time
I try to add the Return Delay Time you mention (https://github.com/ROBOTIS-GIT/dynamixel_hardware_interface_demos)
I forgot the parameter in the tag of gpio. After adding the parameter in my ros2_contro.xacro, the error code is stil existed.

2. System Spec.

• 16 Motors (XC330-M288-T)
• Update rate : 100 Hz
• Baud rate : 4 Mbps
• Hardware interface : U2D2
• Method of cabling : All dynamixels daisy chained

Thanks!

[InguChoi]

Update:
After changing the update rate from 100 Hz to 10 Hz, the error message disappeared:

So it seems that the error is related to the control frequency.
Currently, my system works at 10 Hz without any problem, but I would like to achieve a faster control loop (e.g., 50–100 Hz).

To improve this, I am considering changing the Dynamixel connection structure:

• Right now, all 16 XC330 motors are connected in a single daisy-chain.
• I am planning to try a parallel connection (splitting motors into multiple ports, e.g., per finger or group) to reduce communication bottleneck.

My additional questions are:

1. Is there a recommended connection structure (daisy-chain vs. parallel) when controlling many Dynamixels with ros2_control_node?
2. What is the practical update rate that can be achieved for 16 XC330 motors?
3. Are there specific parameter settings (baudrate, sync read/write options, etc.) that you recommend for higher control frequency?

Best regards,

[Woojin-Crive]

I recommend twisting the TTL cable to improve the electrical environment and reduce noise. I believe the issue is noise-related. In fact, having 16 DXLs on a single TTL bus can be quite challenging.

[Woojin-Crive]

1. I recommend using two U2D2s for this project. There’s also an asynchronous solution for ROS 2 Control, and I can share an example with you.
2. With two U2D2s, achieving around 400 Hz would be ideal.
3. It’s already configured with the optimal settings to achieve high frequency.

[InguChoi]

@Woojin-Crive Thanks! After I try changing the daisy-chain to a parallel structure or integrating it into a dual U2D2 system, I will briefly update the results in the issue.

[InguChoi]

@Woojin-Crive Could you share the example when I use two UD2Ds?

[Woojin-Crive]

@InguChoi

ROBOTIS-GIT/dynamixel_hardware_interface_demos#5

This is still a preparation version, but I’d like to share it with you. I’ll let you know again once it’s merged into the main branch.

[Woojin-Crive]

Also, we’ve recently opened a new Discord server for ROBOTIS — feel free to join and share your experiences or questions there: https://discord.gg/H6exk2dX