Issue with Reading Motor States on Daisy Chained Lynxmotion HT1 Integration with ROS2 Humble

[bely2803]

Hello there! I am currently integrating the Lynxmotion HT1 motors into my robot using this hardware interface. Here is a brief overview of my setup:

Hardware Setup: 4 HT1 motors wired in daisy chain configuration, all running the firmware version 370.
Software Setup: Using ROS2 Humble.

Problem Description:

I am able to send commands successfully to all 4 motors without any issues. However, I encounter a problem when trying to read the motor states:

• Only the first requested state of the first motor passed to lss::Bus::write_slot_config(DeviceIndex& index) in the function LssBusHardware::on_activate(const rclcpp_lifecycle::State &) is received.
• No states are received for subsequent motors.

Workaround:

To resolve this temporarily, I applied a patch that inserts dummy motor IDs between the actual motor IDs passed to lss::Bus::write_slot_config(DeviceIndex& index). With this workaround, I am able to receive all requested motor states.

Example: My motor IDs are {10, 20, 30, 40}, but I modify the call to include {10, 15, 20, 25, 30, 35, 40}.

Questions/Clarification Requests:

• Is this behavior expected due to some internal mechanism of lss::Bus::write_slot_config()?
• Are there recommended settings or configurations that might avoid the need for dummy IDs?
• Is there a potential bug in handling the read states across multiple motors in a daisy chain setup?

Thank you for your assistance and any guidance you can provide on resolving this issue!

[guru-florida]

Hi Yohan. I write position (+more) and read position, state, current back for 18 servos at about 50Hz or so. It should have no problem for 4 servos. Can you share your ros2-controls yaml configs?