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Hank uses bumpers that rest lightly against the touch sensors. When the bumper is pressed anywhere along its length, the touch sensor is then also pressed. A slightly different approach is to make
a bumper that is held tightly against the sensor. When the bumper collides with something, the sensor actually turns
off instead of on.
The trick with bumpers is to make them sensitive but not too sensitive. The bumper needs to trigger the touch sensor when the robot bumps into something. On the other hand, it should not trigger
the touch sensor when the robot starts or stops moving abruptly or when it's driving over a bumpy surface.
Gears
Gears are clever mechanical devices that can be used to trade speed for power or to translate motion from one axis to another. A gear, in essence, is a disk with teeth on its edge. It has a space in its
center where you can put a shaft. Gears have three primary purposes:
1. You can trade speed for power by using a small gear to drive a larger gear. The shaft on the larger gear will turn more slowly but more powerfully than the shaft on the smaller gear.
2. The opposite effect—trading power for speed—occurs if you use a large gear to drive a smaller gear. The shaft on the smaller gear will turn faster than the one on the larger gear, but with less
power.
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3. You can use gears to transfer motion from one axis to another. The gears in Hank's body transfer motion from the motors to the drive axles of the treads, as shown in Figure 2-13.
Figure 2-13.
Using gears to transfer motion
The Palette of LEGO Gears
LEGO offers an impressive array of gears. The LEGO community has adopted names for these gears, which I will use throughout this book. Refer back to Figure 2-3; it shows the gears that come
with RIS and their names. For the most part, gears are named based on the number of teeth they have. The 40t gear, for example, has 40 teeth. The number of teeth is directly proportional to the
gear's radius, so the 24t gear has a radius exactly three times as large as the 8t gear.
Specialty Gears
You're probably comfortable with the 8t, 16t, 24t, and 40t gears. They can be put together to transfer rotational motion from one axis to another. In particular, these gears are used to transfer
motion between
parallel axes.
The gears in the bottom row of Figure 2-3 can be used to transfer motion between perpendicular axes. Two of these are bevel and crown gears.
The worm gear is a real character, for two reasons:
1. While the other gears attach firmly to the shaft, the worm gear can slide freely along the shaft. If you want it to stay in one place, you'll need to anchor it down somehow.
2. The worm gear really works only one way: you drive the worm gear, and it drives another gear. There's no way to turn the other gear and have it translate to motion in the worm gear.