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WW-11 WheelWatcherTM Encoder

When the WheelWatcher servo encoder is added to a standard-size RC servo, it accurately senses direction, distance, velocity and acceleration. Installation is easy using the provided hardware and alignment tool.


  • Dead reckoning
  • Odometry (how far has it gone)
  • Closed-loop position, velocity, and acceleration control
  • Stall detection


  • Easy installation
  • Simple interface
  • Preprinted 32 stripe self-adhesive codewheel included
  • Hardware quadrature decode with 4x multiply for 128 clocks per rotation
  • Raw quadrature
  • Smart serial mode
  • Compatible with standard-size servos from Hitec, Futaba, and GWS
  • Designed for use with standard injection-molded robot wheels any color
  • Adapts to many wheels and articulated mechanisms with optional CS-040 codewheel spacer
  • Code examples for common robot controllers available
  • Fully compatible with Wheel Commander WC-132  (in quadrature mode)


The WW-11 WheelWatcher low cost incremental encoder system enables robot builders to quickly add closed-loop control to their robots. Standard ChA/ChB raw quadrature outputs, decoded Clock and Direction signals, or 38400 baud serial interface modes are available. When in Sign/Magnitude mode, the clock signal toggles at each transition of ChA or ChB, providing a 4x increase in resolution 128 clocks per servo rotation while the direction signal indicates the decoded direction of rotation, making it very easy to add to any microcontroller. Serial mode outputs the distance travelled and current velocity, both in terms of encoder ticks.

Board installation consists of removing the adhesive backing, aligning the board with the shaft, then attaching the board and servo to the robot chassis with the supplied mounting hardware. Codewheel installation is just as simple: peel off the backing, and lower onto the spline-side of the wheel; the raised hub helps align the codewheel to the axis of rotation. Accurate alignment to the servo output shaft is easy to do with the included AL-02 alignment tool.

Differences with the WW-01

The WW-11 differs in these ways:

  • 5 pin, 0.1" pitch connector rather than 8 pin (2 rows of 4) 2mm connector
  • 3 operating modes which can be selected by selectively pulling down certain connector pins:
    • quadrature (ChA/ChB)
    • sign/magnitude (CLK/DIR)
    • serial (38400 baud); outputs distance traveled as well as velocity
  • sign/magnitude mode toggles the clock line on either edge of either quadrature channel, rather than the 50us low pulse on either edge generated on the WW-01
  • thinner board material (0.031" rather than 0.063")
  • no adhesive on back of board

WW-11 encoder with alignment tool

  • Printed circuit board, preassembled
  • Alignment tool
  • Self-adhesive codewheel
  • 6" five lead color-coded cable
  • Mounting hardware
  • Servo and wheel not included
WW-11 Parts

Two wheel WW-11 kit

  • Two WW-11 servo encoders
  • One alignment tool
  • Servos and wheels not included.
WW-11 Parts

  WW-01 Installed

  WW-01 Side  WW-01 Top

Click photo to enlarge. The bottom photos show the older WW-01, though the overall concept is the same.

WheelWatcher encoder shown with servo and wheel sold separately.

 * Requires Adobe Acrobat Reader:


WARNING: the connector silkscreen on Rev A WW-11 boards is incorrect. It says + A M B for pins 1-5, but should read + B A M instead. In other  words, the pin numbering below is correct ignore the silkscreen.

Connector Pinout - J1: 0.1" Pitch
Pin Color Set A Color Set B Quadrature Mode Sign/Magnitude Mode Serial Mode Rev A Label
1. "+" red violet
Vcc (+) between 3.3v and 5.0v
2. "B" orange gray ChB Direction Serial Mode select (if low on reset)  "A"
3. "A" yellow white ChA Clock Serial TX Out (TTL level, non-inverted, 38400 baud, 8-N-1) "M"
4. "M" green black Quadrature Mode Select (if high or floating on reset) Sign/Magnitude Select (if low on reset) Serial RX In (TTL level, non-inverted) "B"
5. "-" blue brown
Gnd (-)

Block Diagram



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