How cab I make a car that will go really slow down a piece of wood?

Question

I have yet ANOTHER extra credit science project due at the end of the grading period. It's supposed to be a car that is TOTALLY hand-made and it has to go down a 3 1/2-4 ft piece of wood at about a 60 degree angle the slowest time possible. So, in other words, it will be slanting down (the highest point is about 3-4 ft. off of the ground) and it CANNOT fall off of the side....AND it has to get to the finish line (the end of the plank at the bottom) in the slowest time than anyone else to get a total of 5 points on the final grade. (That's , like, 25 points extra on a major test grade.) What should I make it out of?

The wheels ahve to be able to move....even a little bit will do.

Answer 1

Hi!
I would try to make a car that had an escapement mechanism, like that in a clock. This is a mechanism that typically rocks from side to side, each time releasing a part of a revolution of the escapement wheel. The idea is that a fork or claw form has a tooth on each side. the teeth on the escapement are almost always touching one or the other of teeth. As the pendulum rocks to one side, the tooth on one side is released, but the tooth on the other side has already engaged to escapement wheel. For more detail see:http://en.wikipedia.org/wiki/Anchor_escapement
http://www.answers.com/topic/escapement

Consider having a car with an axle across the rear with a wheel at each end, and a disc in the middle with say 15 short brads protruding, each spaced equally from the other. across the wheel. The chronometer method here shows a method of making a very accurate escapement.
http://www.abbeyclock.com/bchrono.html
This is difficult to construct.

Depending on how much you have to build yourself, and if you can use a cheap clock mechanism. If you can use a purchased clock, I would go to a craft store for a clock mechanism. These are about an inch and a half square, and cost about $5-$8. On the shaft I would mount a wood wheel with a grove filed into it, making it into a pulley. On the axle shaft, I would have another pulley made the same way. Between the two pulleys I would use a rubber band. With the wheel on the second hand shaft, the clock wheel would turn once in a minute. If the wheels were about 1 inch in diameter. the car would advance down the incline at about 3.14 inches per minute. Using the minute hand shaft, the car would advance at 1/60 of that speed. Using the hour hand shaft, anvancementwould be 1/3600 of the second hand rate. Make sure you select the motor placement correctly or the car will climb further up the grade.

If you have to make everything yourself, the easiest might be to make the drive wheel on the axle have little blades sticking out made from tongue depressors. The paddles would have to turn in a viscous liquid, such as a heavy vegetable cooking oil.

This sounds like a great challenge. I wish you well.

Answer 2

Well, I think the wheels would be a good place to start. First the smaller the diameter and softer the wheels are the more rolling friction they will have. The next step is to gum up the bearings. If you use something uneven or too sticky one wheel might drag more than another and throw the car off the track.

I'd use soft rubber wheels with as small a diameter as possible. Next you need a uniform liquid lubricant that has a high viscosity. Probably best option would be 140 wt. gear oil. That should do the trick.

Answer 3

Use lots of friction, and high coefficient of drag.
Probably best would be to just glue the wheels so they don't turn at all and use tires that have the largest coefficient of friction that you can find. Add large sails to impede motion.
If you're allowed to use a motor, put retro-rockets on it -- powered by compressed CO2-- that push the vehicle in a retrograde motion.