USB Serial Adapter for TreX motor controller

Hi, I have decide to purchase a Pololu TReX Dual Motor Controller DMC01 for my dual motor project and will use the program to configure the board.
Is the Pololu USB-to-Serial Adapter item 391 the correct usb to serial adapter I should use with my pc and the Trex?

Is there a connection diagram for connecting the serial output pins to either the ttl or rs232 pins on the Trex?

Is there a sequence of events like removing jumpers, applying power, or … that needs to be done to get the adapter and configuration utility to recognize the trex.

I have searched the forum and found this:

Re: TReX Jr with USB-to-serial problem

Postby ltdan81 » Thu Nov 26, 2009 5:11 pm
I was having this same problem and it took me a while to figure it out. The problem was that I was following directions instead of what was implied, I guess… I needed to start up with the program jumper on, remove it with power on (the manual explicitly says NOT to do this!) and then attach the serial… basically the firmware flash directions, BUT without removing the mix jumper.

To clarify, here are the exact steps to connect the configuration software via serial connection.

  1. Turn off TReX Jr.
  2. Short SO and GRND
  3. Put on mix jumper
  4. power on TReX Jr.
  5. Remove SO and GRND (leaving power on)
  6. Connect serial cable
  7. Press connect on configuration software.

Is this still correct?



Yes, the Pololu USB-to-Serial Adapter could be used to connect the TReX to a PC. To connect the adapter to the TReX , you would connect the RX pin of the serial adapter to the SO pin of the TReX, the TX pin of the serial adapter to the SI pin of the TReX, and the GNDs of the two devices together. The TReX would also need to be in serial mode, which can be done by removing the mode jumper. There is no special sequence of events needed to connect with the configuration utility; just make sure the jumper is removed before the TReX is powered up so that it starts in serial mode.

  • Grant

Thanks, really appreciate the info. I am planning to configure the trex with the pc utility pgm and run my bot in RC mode at first and maybe monitor the current with my arduinos serial port.

Eventually I will use the ttl serial mode for autonomous control of my bot and use the trexs rc takeover feature when the bot gets stuck.

I am guessing that I will need to adjust one or the others motors speed and possibly acceleration and braking to make the bot drive in a straight line by adjusting the Trim tabs on my rc radio and then also via the speed value sent to the trex for each motor via ttl serial.

Did I guess correctly?


Yes, using the trim tabs is one way to compensate for motor differences. You could also change some of the TReX settings to compensate for the differences in the motors. There are several parameters you could change to accomplish this, but the easiest would probably be the PWM maximum configuration settings. From the configuration parameter documentation:

  • Grant