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SRS Robot Level 3 Parts

The following are suggestions for components that you may want to add to your robot.


Adding encoders to the motors/wheels of your robot will enable it to measure distance traveled.

The SRS is selling WheelWatcher encoders designed specifically for the SRS Robot. There is a PCB that mounts to each motor, a striped sticker for the inside of each wheel, and cables that connect to the motor headers on the ARC board. The WheelWatchers were designed and manufactured by Pete Skeggs / Noetic Design, who makes the WheelWatchers for servo motors. Our version is similar to the WW-02, but without the quadrature decoder. We will be doing the quadrature decoding in software.

We are able to sell the SRS version of the WheelWatchers to SRS Robot owners for $35/pair. If you have purchased multiple kits, you may buy as many pairs as kits. (See the Kit Purchasing page to order.)

If you would like WheelWatchers for a project other than the SRS Robot, you can buy the WW-02 (with the quadrature decoder) from Acroname.


The documentation for our version is included in the standard WW-02 documentation, which is on the WW-02 page. Look for the section "J2: .100" Connector Pinout" for details on the wiring. Pins 1-6 correspond to the 6 pins on the motor headers on the ARC board. You will need to connect the wires from the motors to the WW-02 boards; those signals are connected to the ARC board as part of the 6-pin connection. On the WW-02, pin 2 (Motor+) is connected to SH1; connect the orange motor wire to SH1. Pin 4 (Motor-) is connected to SH2; connect the red motor wire there.

Sample Code

You can download a 9KB zip file with Sample C code in the "Level 1" style (using Util.c and Util.h). Check back for code using classes as in Level 2.

Digital Rate Gyroscope

One way to determine heading for your robot is to use a digital rate gyroscope (also called an angular rate sensor) to measure the rate at which your robot is turning. You can integrate this to figure out how far it has turned.

A gyroscope measures rotation; an accelerometer measures translation.

One popular device is the Analog Devices ADXRS150; the Evaluation Board version comes in a convenient DIP package that will work nicely in the breadboard.

Also check out the options in SparkFun's "Accelerometers" category (which also contains gyros).


For a balancing robot, you need to measure tilt, which can be done with a dual-axis accelerometer. Some options are the Analog Devices ADXL203 and Analog Devices ADXL320 (evaluation boards), and the selection of boards in SparkFun's "Accelerometers" category.

If you are interested in both a gyroscope and accelerometer, look at the Combo Boards at SparkFun.


The Level 2 kit introduced infrared (light) sensors for measuring distance. Sonar (sound) is another way to measure distance, and is generally more reliable outdoors where sunlight tends to saturate light sensors.

The SRS Robot has a chassis plate designed to hold the Devantech SRF04 Ultrasonic Range Finder. This and various other interesting components can be found at the Mark III Robot Store.


One popular compass is the Devantech CMPS03 Digital Compass.