milliaaaa
hey I'm new to this site and i need help I'm in grade 10 and we have to build a car...wait the instructions are right here:

Build a vehicle that will travel down a ramp and then stop at a point 3m away from the base

MUST NOT BE PREFABRICATED

we get to choose the level of the ramp
rpenner
1) This is a test of your ability to come up with a rough plan or design to accomplish the stated goal, test the design and improve on the design until you are happy.
2) None of us are in your class, so we don't know what materials, budget or schedule your class is recommended to use. Tenth grade standards vary from school to school and even from class to class.
3) Depending on design, you will get different results by running your car on an indoor basketball court, clay tennis courts, concrete or asphalt blacktop.
4) Finally, even if we were willing to put our own mark on what should be your accomplishment and design, since this forum is primarily text-only, it's not the best forum in which to discuss 2-D and 3-D engineering design which often requires specialized vocabulary or pictures.

Given that, you have several basic design choices to choose from at the beginning:
1) Basic friction design. You make a car, then add dragging or rubbing parts as needed until the car travels about 3 meters on a flat surface.
2) Engineering measurement of total distance. The car measures many times the wheels turn and snaps on a brake at a predetermined point.
3) Principles of physics. Using a clock, the car snaps on a brake after a certain amount of time has elapsed.
4) Principles of physics II. Using a calculating element, a known ramp incline, and a clock, the car calculates when to apply the brake.
5) ...

All of these depend on a car frame that without the brake/friction parts goes at least 3 meters from the base of a practical incline.
ubavontuba
QUOTE (milliaaaa+Mar 19 2009, 03:08 PM)
hey I'm new to this site and i need help I'm in grade 10 and we have to build a car...wait the instructions are right here:

Build a vehicle that will travel down a ramp and then stop at a point 3m away from the base

MUST NOT BE PREFABRICATED

we get to choose the level of the ramp

Try eccentric wheels (oval/egg shaped, or wheels where the axles aren't centered).
mault
Generally 37 degrees gives most distance for speed

other than that you need to determine the mass of your car and the friction of the wheels for the surface and axels. The determine the distance you get with x length ramp at angle y and extrapolate to 3m...

AlexG
Tie a 3 meter long cord to the rear bumper and the bottom of the ramp.
Granouille
QUOTE (ubavontuba+Mar 24 2009, 09:40 PM)
Try eccentric wheels (oval/egg shaped, or wheels where the axles aren't centered).

Or use an analog solution. Someone here mentioned an analog method of finding pi.

Roll a cylinder of unit radius until it reaches 3, then shave it flat! The wheel will stop. Arrange the dimensions for your experimental setup, and be smiling!

Argyll
Make one of the axles threaded, like a worm gear. Create a block with gear teeth that match the threading of the axle. Set it up so that when the car is on the ramp, the block is off the axle, and when the car goes horizontal the block drops onto the axle.

If you set it up so that the motion of the axle pushes the block from one side to the other, and if you have the threading right, then after about 3 meters the block will be unable to travel any further and the axle will be prevented from turning, stopping the car.
milliaaaa
thanks for the help to everyone we got perfect in the race it stopped right on the dot:D
buttershug
And you did it how?

I was going to offer suggestion back when the thread was new but AlexG stole my idea out of the ether.
AlphaNumeric
QUOTE (AlexG+Mar 25 2009, 08:21 PM)
Tie a 3 meter long cord to the rear bumper and the bottom of the ramp.

It can be done in a way which doesn't require you to tie the car to anything.

Suppose the wheels are of radius R and the axles are of radius r (r<R obvious). For every turn of the wheels the car moves forward a distance 2 pi R. Suppose you have a bit of string length L and you glue an end to the front axle and the other to the back axle. For every turn of the wheels the string will wrap around the axle a length 2 pi r.

If the car is to travel a distance D then the wheels will turn N = D/(2 pi R) times. Therefore if the string is L = N (2 pi r) in length it'll only allow the car to move a distance D before the string is made taut and the car stops. To avoid tangling you initially wind the string around one of the axles (say the back one by spinning the back wheels in reverse).

Putting in the expression for N you have L = (D.r)/R, so if the wheels are, say, twice the thickness of the axles then you need a bit of string 1.5m in length.

So irrespective of how the car is propelled (a slope or using rubber bands etc) the wheels will lock after a distance D, stopping the car. Obviously I'm assuming no skidding etc which can be easily done by making the slope quite gentle.
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