set_multi_position_and_speed succeeds on one port, fails on the other

[ryanoldja]

I have 6 MX-64's assembled in a 6-DOF arm where 3 of the servos are connected via port /dev/ttyACM0 and the other 3 servos are connected via a second port, /dev/ttyACM1.

Through the dynamixel_joint_action_controller, I'm attempting to write commands to all 6 servos using the set_multi_position_and_speed method of the DynamixelIO object. The write command is successful for the three motors on port /dev/ttyACM0, but fails to move the motors on port /dev/ttyACM1.

Through print statements I added in dynamixel_io.py, I can see that the (motor_id, position, velocity) data tuple is properly passed in to the sync_write method, yet the motors do not move. In fact, they even fail to enable torque, which led me to try simply enabling all the motor torques via set_multi_torque_enabled. In this test, I actually succeeded to enable all motor torques over both ports. Since set_multi_torque_enabled also uses sync_write, I'm failing to understand why the set_multi_position_and_speed method is failing on me.