Newer Motor Controllers Available! Pololu generally recommend Pololu's newer, easier-to-use Simple Motor Controllers over the TReX. The Simple Motor Controllers can accept RC, analog, or TTL serial inputs. Additionally they have a USB interface for quick configuration (no need for an external USB-to-serial converter like with the TReX). Pololu's newest G2 Simple Motor Controllers can also be controlled through I²C and have configurable current limiting. Each Simple Motor Controller only has a single motor channel, but they can be connected in mixing mode and used with two analog or RC joystick channels (x and y axes) to control both the motors in a differential drive robot just like the TReX. Note that unlike the TReX, the Simple Motor Controller does not have an RS-232 interface or serial override feature.
Pololu TReX Jr bottom with labels and dimensions |
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A novel blend of serial, RC, and analog motor control
The TReX Jr Dual Motor Controller, a lower-power version of theTReX 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 three 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 24 V.
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:
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. For example, the TReX would be a great motor controller for a remotely controlled balancing robot.
Pololu TReX Jr Dual Motor Controller with labels |
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Technical specifications
Dimensions | 1.75" x 1.75" x 0.5" (0.3"height without connectors) |
Supply voltage | 5 – 24 V |
Primary motor outputs | 2 bidirectional, 5 A peak, up to 2.5 A continuous (may be combined to control 1 bidirectional,5 A continuous) |
Auxiliary output | 1 unidirectional, 10 A continuous |
Speed control | 128 steps in each direction |
Control interfaces | RC servo pulses, analog voltages, or serial commands; master interface set by mode-select jumper |
Input channels | 5 (RC servo pulses or analog voltages) |
RC pulse measurements | 12-bit resolution, 1 us 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 1200to 115,200 bps |
Expanded protocol | Allows multiple Pololu servo and motor controllers on one serial line |
Compact protocol | Allows both motors 1 and 2 to be simultaneously set with just three bytes |
RC/Analog control features
Options accessable through the serial interface
Safety features
Note: The TReX Jr does not require use of the serial interface to function; it will work right out of the box as an electronic speed control (ESC). You will not have access to the full suite of features the TReX Jr provides if you do not make use of the serial interface, though.
24" (600 mm) female-female RC servo extension cable. |
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Servo cable accessories
The TReX Jr has male 0.1" headers; for direct connection to an RC receiver or serial servo controller, Pololu recommend ordering one 6" female-to-female cable, 12" female-to-female cable, or 24" female-to-female cable per channel you intend to use (the TReX Jr can use up to five channels).
People often buy this product together with:
Servo Extension Cable 6" Female - Female |
Dimensions
Size: | 1.75" x 1.75" x 0.5" |
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Weight: | 15 g |
General specifications
Motor driver: | MC33887 |
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Motor channels: | 31 |
Control interface: | non-inverted TTL serial (2-way); RS-232 serial (1-way), RC servo pulses, analog voltage |
Minimum operating voltage: | 5 V |
Maximum operating voltage: | 24 V |
Continuous output current per channel: | 2.5 A2 |
Peak output current per channel: | 5 A3 |
Continuous paralleled output current: | 5 A |
Current sense: | 0.5 V/A4 |
Maximum PWM frequency: | 10 kHz |
Minimum logic voltage: | 2.7 V |
Maximum logic voltage: | 5.5 V |
Reverse voltage protection?: | Y |
Notes:
Documentation and other information
Pololu TReX Jr User’s Guide (Printable PDF)
User’s guide for the Pololu TReX Jr motor controller
Sample C# Program for Communicating with the TReX and TReX Jr (Printable PDF)
This sample C# program (written for Microsoft Visual C# 2008) shows how you can use your computer to send and receive data from the TReX and TReX Jr motor controllers.
File downloads
TReX Configurator utility for Windows version 100608 (295k zip)
If you have the ability to connect your TReX to a computer (via serial port or USB-to-serial adapter), you can use this program to monitor the channel inputs, control the motor drivers, and configure its various settings. This version supports TReX and TReX Jr firmware versions 1.3 and below. Please manually uninstall older versions of the TReX Configurator before installing this version.
TReX Jr command documentation (100k pdf)
TReX Jr (DMC02) Firmware version 1.2 (161k trx)
This firmware fixes a bug that affected the 38,400 and 28,800 bps baud rates, and it adds a configuration parameter that lets you optionally insert a 1 ms delay between the last byte of a received command packet and the first byte of the TReX Jr’s transmitted response. Without this delay, slower controllers, such as the Basic Stamp, can miss the first byte of the TReX Jr’s response.
MC33887 motor driver datasheet (1MB pdf)
Drill guide for Pololu TReX Jr Dual Motor Controller DMC02 (85k dxf)
This DXF drawing shows the locations of all of the board’s holes.
Recommended links
Arduino example code for the TReX
This Arduino sketch, written by forum member mwomack, sets up a serial interface between the TReX and an Arduino and sends three basic data-query commands: “Get Signature”, “Get Mode”, and “Does Serial Control Motors?”. It can be used as a template for implementing additional commands.
More Arduino example code for the TReX
This Arduino sketch, written by forum member gcebiker, sets up a serial interface between the TReX and an Arduino and sends commands to drive motors in response to joystick inputs to the Arduino.
Video of the RP5 Tracked Chassis Driven by the TReX Jr
A video showing the RP5 Tracked Chassis as a radio-controlled platform driven by the Pololu TReX Jr motor controller.
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