TReX Jr Dual Motor Controller


The TReX Jr Dual Motor Controller, a lower-power version of the TReX Dual Motor Controller, is a versatile DC motor controller designed to seamlessly blend autonomous and human control of small robots. The TReX Jr can control two bidirectional and one unidirectional motor via multiple independent control interfaces: radio control (RC) servo pulses, analog voltage, and asynchronous serial (RS-232 or TTL). Using the compact MC33887 motor driver allows for a single-board design that reduces cost while maintaining a small package. As an added benefit, the use of the MC33887 motor driver allows operation to 24V.

The TReX Jr uses five input channels to receive the RC or analog control signals. When operating in RC or analog mode, the five channels function as follows:
Channel 1: motor 1 speed and direction or, if in mix mode, turn left/right
Channel 2: motor 2 speed and direction or, if in mix mode, go forward/reverse
Channel 3: auxiliary (unidirectional) motor speed
Channel 4: can be used to enable “flipped mode”, which allows invertible robots to be controlled as normal when they are inverted
Channel 5: determines whether the motors are controlled by the channel inputs or the serial interface; this channel allows you to switch between autonomous and human control at will.

The serial interface can switch instantly with one of the other two interfaces, allowing mixed autonomous and remote control. For example, a robot could be configured to run autonomously most of the time, but a human operator could override the autonomous function if the robot gets stuck or into a dangerous situation. If the serial mode is selected as the primary interface, high-resolution measurements of all five channel input signals (be they RC pulses or analog voltages) are made available to the autonomous robot controller, allowing for complex and unlimited mixing of operator control and sensor input. 

Motor Driver: MC33887
Current sense: 0.5 V/A
Maximum PWM frequency: 10 kHz
Reverse Voltage Protection: Yes
Auxiliary Output: 1 unidirectional, 10A continuous
Speed Control: 128 steps in each direction
RC Pulse Measurement: 12-bit resolution, 1µsec accuracy
Analog Measurements: 10-bit resolution
Serial Interface: both RS-232 and TTL (logic level), bidirectional
Baud Rates: supports 11 common baud rates ranging from 1,200 to 115,200 bps
Expanded Protocol: Allows multiple Pololu servo and motor controllers on one serial line
Compact Protocol: Allow both motors 1 and 2 to be simultaneously set with just three bytes

Tech Tips:

TReX Configurator utility for Windows version 100608
TReX Jr command documentation
TReX Jr configuration parameter documentation
TReX Jr (DMCO2) Firmware version 1.2


User Manual 



RC/Analog control features

  • Battery Elimination Circuit (BEC) jumper lets the TReX Jr optionally power your RC receiver or analog controller
  • mix-mode jumper allows for single-stick motor control of differential-drive robots
  • automatic calibration for your particular RC or analog controller (the TReX Jr can learn the channel ranges)

Options accessible through the serial interface

  • all five high-resolution channel input values are available
  • remapped channel input values show what the TReX Jr would do if it were in control
  • optional 7-bit cyclic redundancy checking to ensure command/data validity
  • calibration values can be explicitly read and set
  • each channel can be reversed and parabolically scaled
  • current limit, acceleration, and maximum motor speed settings
  • the bidirectional motors can (individually) be set to coast or variable brake when in the deadband
  • upgradable firmware

Safety features

  • “safe-start” requirements prevent accidental motor activation at power-up
  • optional automatic motor shutdown on serial error, timeout, or input channel noise


Channels 3
Motor Type Brushed DC
Weight 0.53 oz (15g)
Control Input non-inverted TTL serial (2 way); RS-232 serial (1-way), RC servo pulses, analog voltage
Input Voltage Range 5 – 24V
Input Signal Voltage Range 2.7 – 5.5V
Max Current per Channel (Continuous) 2.5A
Max Current per Channel (Peak) 5A