I looked at the various VIs that come with the LabView API for the Dynamixel SDK which is set up in a similar manner to the C/C++ API that I am more familiar with. And the bad news is that both APIs are not exposed at a level low enough so that a user can manipulate the Rx/Tx Flow Control at will.
The Data Flow Control implemented on the U2D2 is explained some more here (and it won’t be easy to implement from scratch in software):
If you do not want to use a USB Hub then may be your other device can be hooked up to I2C or SPI? If not you don’t have a choice but to use a USB Hub on your myRIO.
Or another approach is to use an Arduino Board to control all your Dynamixels, such as an OpenRB-150 (OpenRB-150) - then you’ll have to use C/C++. In this case, the MyRIO can be used in a supervisory level talking to the OpenRB-150 via UART Ports on both sides? Just send ASCII packets back and forth? Of course, this approach comes with a Systemic Delay via the UART Ports that can’t be avoided.
The Arduino Library is called Dynamixel2Arduino and its C source code is available here:
UPDATE: ALSO I just remembered this article about a replacement for a U2D2 via a PCB, but it was for an RPi4B’s UART Port which operates at 3.3V (which is not a problem with myRIO).
Also read this follow-up post on the same issue: