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Castor Bot
Building: Advanced


Building Instructions














Use two medium length wires to connect the two drive motors to ports B and C on the NXT. 

Important: Keep the left wire on the left and the right wire on the right (do not cross the wires).


Building Tip: Weight Balance

When building a robot with a castor wheel, it is important to consider the weight balance of the robot.  For good turning, you want to have most of the robot's weight over the drive wheels, if possible.  But there must also be enough weight over the castor to keep the robot stable and avoid tipping over.  If too much weight is over the castor, the robot may struggle to turn, might get caught up and stall, or the drive wheels might start slipping.  However, if too much weight is over the drive wheels, the robot may pop a wheelie if driven with a lot of power with the drive wheels in the back (see the Dragster).

As determined by the experiment below with a small scale, this Castor Bot robot has a total weight of 600 grams, with 388 grams over the drive wheels.  This works out to 65% (388/600) of the weight over the drive wheels.

The Castor Bot's total weight is 600 grams 388 grams (65%) is over the drive wheels


Castor Bot Programming

The Castor Bot is a basic two-motor drive robot with sturdy construction that turns easily.  You can use it as a starting point for your own projects, and program it however you want.  To get started, you could try the "NXT Program" feature of the NXT brick to select some simple movements using the buttons on the NXT brick.


  • Write some simple programs to make the Castor Bot move, turn, etc.  Use "Move" blocks with the motors set to C and B.  As built, the castor is on the back of the robot, so motor C is on the left and motor B is on the right, but you can just as easily drive it "backwards" if you want.

  • Make some attachments to add to the Castor Bot with sensors, etc.  For example, you could add a sound sensor to make the robot alternate between going and stopping whenever it hears a sound.

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