I tried the Hylands half-duplex trick of just tying together tx and rx with a UM232R. It appears to work. It basically creates a loopback where any data that is sent is received back immediately. Due to the delay in the dynamixel(s) response it is able to have the packet consumed before the response arrives. That's the theory at least.
Pros: Less parts.
Cons: Extra software required to ignore sent packets.
The big question is whether this is a good/safe idea? A secondary question is how is performance effected due to the extra data being looped back.
So after it was working I had the bright idea of removing the USB-B connector from the board so I could mount a USB-A connector off board. Maybe this time I will learn.. Taking off USB connectors is a bitch! Next time I am going to just destroy the thing leaving only the pins standing.
Of course when I get the connector off I have destroyed the vias. After soldering on the USB-A pigtail the thing no longer worked. I could easily make sure power and ground were working, but D+ and D-. Luckily there were two other tiny vias on the board. After looking at the schematic I determined that they were indeed solder spots that would work out. There were!
Here it is in its "finished" RC style shrink wrap glory. It's about twice as thick as it should be because I decided to use a dip carrier instead of more soldering directly onto the module. I'll probably end up using this as a 3.3V USB-serial device so I should make it easy enough to disassemble without destroying more pins.
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