Picture of Introduction: SpurtBot ShadowRunner
SpurtBot Shadow Runner Schematic.jpg

Spurt is an abbreviation of: School Projects using Robot Technologies. The SpurtBot ShadowRunner is a simple shadow avoiding robot. It will go straight until the sensor is in shadow, then back up and turn.

NOTE: After you have built and enjoyed your Shadow Runner, you may be able to adapt it by creating new circuits to control its behavior. I have an earlier Instructable on building a line following robot based on a similar design, but without the solderless breadboard. With a few alternative components, you should be able to adapt the SpurtBot as a line follower. Or create a whole new behavior with a circuit of your own design!

I designed this robot to be used for teaching young kids. Children can work with an assistant to build their very own SpurtBot that they can take home. If you want you can pre-build part of the robots so that wires are pre-soldered, and stripped. This way kids just need to assemble the kit.

The video below may be helpful, if you want to see someone walk through the build

Learning Objective

I've used this design and similar to run single day workshops and multi-day robotics classes for children. By making this simple robot, children and students of all ages will learn several basic concepts used in robotics. These concepts include differential steering and motor control, sensors, and automated behaviors. In addition, students will gain experience with hands on construction and prototyping a circuit on a solderless breadboard.

A version of these instructions can be found at:


The Shadow Runner will run from shadows. That is, it will drive forward in normal lighting conditions, but if you cover its light sensor with your hand or it runs into shadow, it will reverse and turn.

In many cases, this will remove the robot from shadow and it will start to drive forward again. A disadvantage of this simple robot is that if it drives too far into shadow, it will just spin in circles on one wheel! Then you will have to ‘rescue’ it.

Note that the Shadow Runner needs a well lit room to operatate properly.


Refer to the circuit diagram in the second picture. When the photo resistor sees light, the robot will drive forward. Both left and right motors are receiving 9V via the normally closed contact of the relay.

When the photo resistor is in shadow, its resistance increases dramatically, and the voltage divider formed with the potentiometer (a ‘pot’ is a variable resistor) now increases the voltage at the input of the two BC337 transistors. These transistors work like electrical switches. They turn on when they get enough voltage to their base input. When used together in a Darlington array, they can provide a lot of current. When they turn on, they provide current to the coil inside the relay, turning it on.

Now the left motor will get ground on its + lead, and 9V on its - lead, reversing the motor.

The right motor's - lead is hard wired to ground from the battery. Since the + lead of the right motor is now also getting ground, the right motor will stop.

This combination causes a stop, backup and turn maneuver. If this maneuver removes the shadow from the photo resistor, it will revert the relay to its normal position, and both motors will drive forward again. If the robot stays in shadow, it will spin in circles with the right motor stopped and the left in reverse.

makesomeso1 year ago

really cool!!

i like your all spurt robots.

Very cool, pretty clever there with the relay! I had my scouts build these. Here's mine running around the kitchen: https://www.youtube.com/watch?v=0VKtpQ8i1AU&feature=youtube_gdata_player
ignoblegnome (author)  mitch_feaster1 year ago
Yay! Nice to see the ShadowRunner worked out well for you.
You can also check out my other SpurtBot designs. You can re-use the body of the Shadow Runner and try the line follower (http://www.instructables.com/id/Build-a-SpurtBot-Line-Follower/) or light follower (http://www.instructables.com/id/SpurtBot-Light-Follower-Rocket-Brand-Studios-Tadpo/)

Have fun!
Zach0z3 years ago
Huh, well I feel silly now. Don't know how I missed that, but thanks anyway!
Zach0z3 years ago
Hey ignoblegnome,
Do you think you could post a schematic for the bot? It'd be a big help as I'm using a different relay and several other parts.
ignoblegnome (author)  Zach0z3 years ago
The schematic is posted as a picture in the Intro section. It is the 2nd picture, right at the top if the Instructable.