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OBJECTIVES:
You will learn how to use gears to increase speed of rotation
and increased torque out of a machine.
STEPS TO FOLLOW:
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A Two-Gear Gear Train: Build a wall or gear platform
to support two gears.
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Write and download a program to the RCX which
will do the following:
Reset the rotational sensor.
Display the rotation sensor value.
Run the motor for 2 seconds and brake.
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Use gears with the number of teeth specified in Table 1 on the
Student Data Sheet.
Record the rotation count for both gears in Table 1 on the
Student Data Sheet. (You will have to run your program twice for each gear combination, connecting the rotation sensor to each gear axle in turn.)
What relation do you see between the ratio of the number of teeth on the gears and the ratio of the count numbers? If the first gear turns clockwise, in what direction does the second gear turn?
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Multiple Gears/Idler Gears:
Now line up more than one gear and attach them to your frame.
Use Table 2 on the Student Data Sheet.
On your gear frame attach the combinations of gears specified
in Table 2, run your program
and read the rotation count for the input gear and the output gear. Compute the
gear ratio for the combination.
The middle gear(s) is called an idler.
What effect do the middle gears have on the gear ratio of the input to output gears? What effect do the middle gears have on the direction the output gear turns with respect to the input gear?
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MATERIALS:
LegoTM Mindstorms Robotics Invention System
with Rotation Sensor
PC computer with USB port and spreadsheet software (such as EXCEL)
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Compound Gears: What is the largest gear ratio we can obtain with our 8, 16, 24
, and 40 tooth Lego gears? We can create larger gear ratios using compound gear
trains. Build a gear box which will allow compound gears to be connected.
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Now study the gear ratio for the box. Run your program and connect the rotation sensor in turn to each of the gears in the gear box.
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Modify the gear box as shown :
Turn the left handle and then turn the right handle. What do you notice about the amount of effort it takes to turn the two?
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Snail Car: Build a snail car which will move as slowly as possible. Have a contest to see which team can build the slowest car.
Here are the rules:
Your car must be built entirely from Lego parts.
Your car cannot move backwards or sideways.
The RCX must be part of your car.
The car must be visibly moving forward at all times.
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