Hi @hehonglu123 . Yes, they do support velocity control. Hopefully it goes without saying but care should be taken when running a joint in velocity control mode to avoid collisions and manage termination conditions well.
MODE_VEL_PID and MODE_VEL_TRAJ are specific to the steppers. Functionally they are similar (though MODE_VEL_TRAJ utilizes an underlying trajectory generator, allowing you to set acceleration limits.
With the Dynamixels you can use the enable_vel and set_vel interface.
The update rate of 15-25Hz is the fastest we can achieve in Python. Note, however, that the actual control of joint velocities is done on the joint microcontrollers.
We have some ongoing work to close a Python control loop around the Dynamixel velocity commands. We’re finding that the actual performance of smooth motion is dependent on the achievable update rates. We are still working on providing more reliable update rates that are not impacted by the user process load.
We’re happy to provide additional guidance if you can tell us more about your application.