# King of the Hill Competition

But what is the "Resistance" of a DC motor?I'm not sure what you're asking. Are you looking for a resistor to control the speed of the motor, or one to limit the voltage that the motor gets? If you are looking for a resistor to limit the voltage, you might want to get something like this:http://www.hobbyking.com/hobbyking/s...ducts_id=686If you are looking for a resistor to control the speed, you might want to get something like this:http://www.hobbyking.com/hobbyking/s...ducts_id=686f

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## Homework Statement

My first-year college engineering design class was tasked with building a vehicle that can make it up a ramp of 5' in length that is at a 45 degree angle. At the top of the ramp is a 2' flat platform. The ramp (both the ramp itself and the platform at the top) is covered in outdoor carpet.

We must build a vehicle that can climb the ramp, park itself securely at the top flat section, and stay there. At the same time, it must be able to ward off an approaching vehicle that will be coming up the other side of the ramp.

## Homework Equations

N/A. One stipulation is that the vehicle must not bore itself into the ramp. Another stipulation is that the vehicle cannot be remote-controlled.

## The Attempt at a Solution

This project doesn't start for another month, but the professor talked about it today in class and I want to get a jump on it.

My though is a vehicle that has only enough power to take it to the top. It must do so fast, otherwise the other "attacking" vehicle will get there first and have an advantage (it can secure itself to the top in before I get there).

I envisioned a vehicle that speedily got to the top, threw out cables on either side of the ramp with hooks to catch the carpet. This would be like burrs that catch on your clothes if you jog through the woods.

The device could also have "flailing" rigid arms that would be comprised of metal rods that rotate at the direction of an incoming vehicle.

Any other ideas? This is definitely a huge modification from the other "King of the Hill" competitions I've seen online and on Youtube.

What material has the highest coefficient of static friction on your carpet? Maybe you could get it to the top fast, drop the wheels or lower the chassis and let some velcro or something under the chassis do some work.

What material has the highest coefficient of static friction on your carpet? Maybe you could get it to the top fast, drop the wheels or lower the chassis and let some velcro or something under the chassis do some work.

I'm sure rubber would have the highest coefficient of friction on carpet. I can go to the local hobby shop and pick up four wheels from an RC car.

I like your idea for having the wheels drop to lower the chassis and then affix the car with industrial-strength velcro.

I guess the big question now is how to get the car to stop at the top and only at the top. I'd have to have a way to "wind it up" and make it stop when it's flat (maybe some kind of gyroscope)... Ideas on this?

I have an iPod Touch. I wonder if I could somehow create a simple app that interfaces with the accelerometer and causes the device to stop when it senses that the car is level.

I'm thinking a simple mercury switch could tell when it has reached the top...
You'd need a latching circuit that holds when the switch is tilted and resets when it "levels out."

I was starting to fall in love with the mercury switch idea but the professor said we can't use any dangerous chemicals or substances... And she specifically named mercury switches.

More info: the ramp is 120cm long on both legs and the plateau is 30cm long. The whole ramp is 30cm wide.

Weight of vehicle must not exceed 2kg.

Vehicle must be powered only by batteries up to 9v and totaling no more than 9v, rubber bands, or mousetraps.

I will revisit the iPod accelerometer idea. There has to be a simpler mechanical means of causing the device to stop on top...

Make your own tilt switch. You could use popsicle sticks (which are very light weight) to create a pendulum. Attach a paper clip that makes contact with a small piece of sheet metal when tilted over, say, 30 degrees.

Make your own tilt switch. You could use popsicle sticks (which are very light weight) to create a pendulum. Attach a paper clip that makes contact with a small piece of sheet metal when tilted over, say, 30 degrees.

That works for me... Mechanical, easy to make, and no chemicals. I'll try it tonight.

Now for getting up the ramp...

I want to use a small, high RPM electric DC motor such as the one here:

http://www.hobbyengineering.com/H4468.html

I know that the speed of a DC motor is directly proportional to the voltage supply. So, in theory, I should be able to hook up the DC motor to a small variable resistor to make speed adjustments... Right?

But, what kind of resistor should I get? I know Ohm's Law is V=IR (Voltage = Current * Resistance) but I'm stuck on how to apply it in this case.