Racecar

Click here for instruction to build a racecar.

Can you spell racecar backwards?

Then get a ruler or measuring tape.

Start your engines ....

Put something in front of the car like a can or a box, so that the sensor shows a reading less than 10 (look at the bottom right corner of the programming screen).

Program the car so it stays in place until you remove the object.

Another start

Instead of an object in front of the car, write a program so it stays (hint: the hourglass block), and then starts when there a loud noise (mircophone block).

Time Trials

Program your racecar to move at power=8, forward, for 2 seconds. Put a stop as the final block.
Measure how far it went in 2 seconds.
Change your program for power=4 for two seconds. How far do you think it will go, farther or less?
Try it. How far did it go?
Change your program for 6 seconds. Predict how far it will go in 6 seconds. Leave plenty of space on the floor when you try!
Was your prediction close? (It might not be perfect since the wheels can slip or other interference.)

Write down how far the car travels each time. You could use a chart like this.

Power Seconds How far?

8 2

4 2

4 6

Try other combinations!

Pit Stop

Have you seen real racecars stop in the pit to change tires when they wear out?

Our Lego tires don't wear out, but let's make a pit stop to change the SIZE of tires. Your set has large and small tires. Whichever ones you built with, switch them for the other size.

Now re-run your trials. At the same speed and power, how far does the car go with different sized tires?

Modifications

Try this!

Take the blue disk off of the motor. Replace it with a small yellow donut (called a bushing). Put the red band back on.

Now re-run your trials. At the same speed and power, how far does the car go with the yellow bushing?

Switch the yellow bushing and the blue disk on the axle, so that the yellow bushing is on the axle and the blue disk is on the motor.

One more trial! Which arrangement would you recommend for a fast racecar?

Gearing Up for the next race

Right now our racecar is driven by a band which connects the motor's blue wheel to the blue wheel on the axle.

You can also use gears to do this. In fact, real cars have a box full of gears called a transmission. Let's modify our racecar. Follow these step-by-step instructions.

Take off the motor

Remove the two yellow wedges.

Remove the wheel, rubber band, and the two blue drive wheels.

Put middle-sized gears on the axle and on the motor.

Replace the wheel. Replace the motor so the teeth on the gears meet.

Try the same experiments we did before. Does the car move farther or less with the same number of seconds?

You also have a teeny gear and a big gear. Try them out in different combinations: big and small, big and medium. You'll have to put the motor in a different place with different gears so the teeth still fit together.

Which combination moves the car the farthest with the same program?

Which one is faster?

Keep track of the differences, in a chart like this.

Write down how far the car travels each time. You could use a chart like this.

Power Seconds Motor Gear - Wheel Gear How far?

6 3 Medium - Medium

6 3 Big -- Medium

6 3 Big - Small

6 3 Small - Big

Try other combinations!

EXTRA CHALLENGE !!

Here's a building and thinking challenge for you.

Build a rectangular frame, like you see here . Just the frame. Keep your racecar. Invent a way to connect it to the front or the back of your racecar.

Put the big gear on the motor and the small one on the axle.

Load up the frame piece by piece with Legos, small toys, or whatever, until the car cannot start to pull it any more.

Now switch the gears to the two medium gears. Can it pull now?

Think about how you trade speed and power.

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