Page 38 - The Unofficial Guide to Lego Mindstorms Robots

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Hank is a pretty simple robot, but you still may run into trouble:

• If your robot spins in place or goes backward instead of forward, you may need to adjust the wires that connect the motors to
the outputs. Remove one of the wires and turn it 180° around. This will reverse the direction of the attached motor. If the robot
is moving backward instead of forward, turn both wires around.

• Hank may not run well on very thick carpet, because there's not much space between the bottom of the body and the floor.
Once you've got things running smoothly, read on. I'll describe Hank's most interesting features in the rest of this chapter.

Locomotion

Hank gets around in the world on a pair of treads, like a tank or a bulldozer. This is just one approach to the general problem of
locomotion. Different designs have different merits - you should choose a locomotion method based on what kind of terrain
you're expecting your robot to encounter.

T reads

Hank's treads have some interesting properties. Foremost among these is zer o turning radius, which is a fancy way of saying
that a treaded robot can turn around in one place. (I'll explain why it's a radius a little later.) Each tread is driven by one of the
motors, so all you need to do to turn is move the treads in opposite directions at the same speed. This turning, however, is
accomplished with a good deal of friction. Both treads slip on the driving surface. Tanks in Veteran's Day parades can really
c hew up roads this way.

The large surface of the treads is one of their other assets. Treads are good for driving on jagged or slippery terrain. Hank
sh ould do pretty well driving over uneven obstacles, like a small pile of LEGO bricks.

D ifferential Drive

Treads are a special kind of differential drive, in which two wheels are each driven by a motor. The wheels are mounted on
either side of the robot, like the treads. Figure 2-7 shows a top view of su ch a robot.

Independent drive wheels behave a lot like treads. If you run them both forward at the same speed, the robot moves forward.
Run the drive wheels in opposite directions, and the robot will spin in place. This design also exhibits zero turning radius, but
without the slipping of the treads.