Pololu Jrk 21v3 USB Motor Controller with Feedback

Not recommended for new designs: Pololu strongly recommend Pololu's newer and better (and smaller) Jrk G2 21v3 USB Motor Controller with Feedback over this controller, as it offers increased power and many other improvements at the same price. Pololu are continuing to offer the original Jrk 21v3 for now as a legacy product for those with systems designed specifically for this controller.

The Jrk 21v3 is a versatile, general-purpose motor controller that supports a variety of interfaces, including USB. The broad operating range from 5 V to 28 V and continuous output current of 3 A (5 A peak) allow this board to control most small DC brushed motors. Analog voltage and tachometer (frequency) feedback options allow quick implementation of closed-loop servo systems, and a free configuration utility (for Windows) allows easy calibration and configuration through the USB port. A USB A to mini-B cable (not included) is required to connect this controller to a computer.

Key improvements over competing products and earlier Pololu motor controllers with feedback include:

• USB connectivity with emulated serial (COM) port allows direct motor control from a PC.
• Ultrasonic PWM to eliminate switching-induced motor shaft hum or whine.
• Robust, high-speed communication protocol with user-configurable error condition response.
• High internal resolution (12 bits) for smooth and flexible calibration to various input and feedback devices.
• Current sensing and limiting.
• Reversed power protection.
• Field-upgradeable firmware.

The table below lists the members of the Jrk family, including the original (green) and newer G2 (black) versions, and shows the key differences among them.

	Jrk 21v3	Jrk 12v12	Jrk G2 21v3	Jrk G2 18v19	Jrk G2 24v13	Jrk G2 18v27	Jrk G2 24v21
Recommended max operating voltage:	28 V(1)	16 V	28 V(1)	24 V(2)	34 V(3)	24 V(2)	34 V(3)
Max nominal battery voltage:	24 V	12 V	24 V	18 V	28 V	18 V	28 V
Max continuous current (no additional cooling):	2.5 A*	12 A	2.6 A	19 A	13 A	27 A	21 A
USB, TTL serial, Analog, RC control:
I²C control:
Hardware current limiting:
Dimensions:	1.35" × 1.35"	1.85" × 1.35"	1.0" × 1.2"	1.4" × 1.2"		1.7" × 1.2"
1 Transient operation (< 500 ms) up to 40 V. 2 30 V absolute max. 3 40 V absolute max. * Reduced from “3 A” based on newer, more stringent tests. The value now is directly comparable to the rating for the newer G2 21v3.

Main Features of the Jrk 21v3

• Simple bidirectional control of one DC brush motor.
• 5 V to 28 V operating supply range.
• 3 A maximum continuous current output (5 A peak).
• Four communication or control options:
  1. USB interface for direct connection to a PC.
  2. Full-duplex, TTL-level asynchronous serial interface for direct connection to microcontrollers or other embedded controllers.
  3. Hobby radio control (RC) pulse width interface for direct connection to an RC receiver or RC servo controller.
  4. 0 V to 5 V analog voltage interface for direct connection to potentiometers and analog joysticks.

• Two closed-loop feedback options:
  1. 0 V to 5 V analog voltage.
  2. Frequency/tachometer digital input up to 2 MHz with 1 ms PID period.
     (Open-loop control with no feedback also available.)

• Simple configuration and calibration over USB with free configuration program for Windows.
• Configurable parameters include:
  • PID period and PID constants (feedback tuning parameters).
  • Maximum current.
  • Maximum duty cycle.
  • Maximum acceleration.
  • Error response.
  • Input calibration (learning) for analog and RC control.
• Optional CRC error detection eliminates communication errors caused by noise or software faults.
• Reversed power protection.
• Field-upgradeable firmware.
• Optional feedback potentiometer disconnect detection.
• Comprehensive user’s guide.

Specifications

The Jrk 21v3 is the smaller of two Jrk motor controllers. For a higher-power version, see the Jrk 12v12.

Included Hardware

The Jrk 21v3 is available in two versions: “fully assembled” with terminal blocks and 0.1" male header pins pre-installed (left picture above), and connector-free (right picture above). The connector-free version includes a straight 0.1" breakaway male header strip and two 3.5mm, 2-pin terminal blocks, but these parts are not soldered to the board, which allows for custom installations.

The three mounting holes are intended for use with #2 screws (not included).

Example Feedback System – 4 Methods of Control

USB control.	TTL serial control.
RC / pulse width control.	Analog control.

Dimensions

General specifications

Notes:

1

Without included hardware.

2

Autodetects baud rates between 300 and 115,200 bps, or can be set to any fixed baud rate in this range.

3

Current readings are converted to a digital number from 0-255.

4

In RC mode, the pulses can be as low as 2V.

Documentation and other information

• 

  Pololu Jrk USB Motor Controller User’s Guide (Printable PDF)

  The user’s guide for the Jrk 21v3 USB Motor Controller and the Jrk 12v12 USB Motor Controller.

• Pololu USB Software Development Kit

  The Pololu USB SDK contains example code for making your own applications that use native USB to control the Jrk Motor Controller, Maestro Servo Controller, Simple Motor Controller, or USB AVR Programmer.

• 

  Application Note: Using AutoHotkey with Pololu USB Products (Printable PDF)

  An application note about using AutoHotkey for Windows to control Pololu USB products.

File downloads

• Jrk Motor Controller Windows Drivers and Software (release 121204) (5MB zip)

  This ZIP archive contains the installation files for the Jrk Configuration Utility, the Jrk command-line utility (JrkCmd), and the Jrk drivers for Microsoft Windows.

• Jrk 21v3 settings for linear actuators (1k txt)

  Use a Jrk 21v3 to precisely control Pololu's Concentric LD series linear actuators with feedback. Instructions for using this file can be found on the linear actuator product pages.

• Dimension diagram of the Pololu Jrk 21v3 USB Motor Controller with Feedback (402k pdf)

• 3D model of the Pololu Jrk 21v3 USB Motor Controller with Feedback (10MB step)

• Pololu Jrk 21v3 USB Motor Controller with Feedback drill guide (60k dxf)

  This DXF drawing shows the locations of all of the board’s holes.

Recommended links

• The Haunted Organist

  A spooky animatronic skeleton using the Jrk USB Motor Controller. See the final result. By Mark Goodson, October 2009.

• R2D2 dome position control

  A replica of the famous Star Wars droid R2D2 that uses the Jrk USB Motor Controller for position control. See the video which shows the Jrk Configuration Utility in action, or read the blog post which has more information. By ggpipe, February 2010.

• Microsoft .NET Framework 3.5

  The Microsoft .NET Framework version 3.5 is required for many Pololu configuration, control, and utility programs under Windows. Most computers will have this installed already or can automatically install it over the internet, but you can also get .NET 3.5 directly from Microsoft at this link. If you are installing on a computer without internet access, make sure to get the Full Redistributable Package.