Most efficient braking system

[Snake]

I intend to do a project based on the occurence of eddy currents, so I decided to do a project involving eddy currents. My project will essentially be a modified bicycle with instead of a wheel the the back will have an 1- 1 1/2 inch thick aluminum or copper disk.
I will possibly use electromagnets or some neodymnium magnets to induce eddy currents in the disk. THis is possible with the help of a friend peddling on the bike. The disk will obviously be elevated off the ground, other systems will probably include samples of rubber from high to low density to represent cost efficiency. High density being expensive, low density being cheap.
My question is is this project able to be done by April 12, and is it advisible for an 8th grader to do?

[deleted-71552]

I intend to do a project based on the occurence of eddy currents, so I decided to do a project involving eddy currents. My project will essentially be a modified bicycle with instead of a wheel the the back will have an 1- 1 1/2 inch thick aluminum or copper disk.
I will possibly use electromagnets or some neodymnium magnets to induce eddy currents in the disk. THis is possible with the help of a friend peddling on the bike. The disk will obviously be elevated off the ground, other systems will probably include samples of rubber from high to low density to represent cost efficiency. High density being expensive, low density being cheap.
My question is is this project able to be done by April 12, and is it advisible for an 8th grader to do?

Hello, Snake!

It sounds like your plan is to replace the wheel of a bicycle with the metal disc, have your friend pedal the bicycle to get the disk rotating, and then use magnets to create a frictionless braking effect on the rotating metallic disk. Do I have that right?

Bravo to you for this project idea. It sounds fascinating!

My concerns about the advisability of this project and your ability to get the project done by 4/12/2007 have nothing to do with your grade in school. I am concerned about the practical problems of creating the disk, doing the work to connect it to the bicycle, and obtaining magnets powerful enough to produce a measurable braking effect on the wheel. I think a large solid copper disk and the magnets to brake it are very expensive.

A more practical alternative would be to create an experiment on a smaller scale - a rotating disc much smaller than a bicycle wheel, or some kind of track or slide to simulate the end of a rollercoaster run. Maybe attaching metal plates to the spokes of a small bicycle wheel.

Perhaps you or some of the experts in this forum could suggest alternatives?

[deleted-71576]

I agree. While bicycle wheels are machined to very high tolerances, and are amazingly frictionless in their bearings, it's probably too much so for this. The wheels have large amount of mass, and can spin at very high rates.

It's both a good news, bad news issue. The deceleration will largely be caused by your braking, and less so by friction of the bearings and aerodynamic braking force (bicycle wheels are very aerodynamic - expensive ones are unbelievably aerodynamic.) So you should be able to get clean data.

The bad news is that I would think you would indeed need to generate a large amount of braking force, which might be a little complicated to engineer, and expensive to implement.

I agree with OneBriiguy - this sounds like a really, really interesting experiment. But time will be short, and design will be key - there won't be much time for missteps, which indeed are an integral part of science.

Certainly don't want to discourage you. Just understand that you have to hit the ground running almost instantly. There are some engineering experts here who should be able to provide help / hints, but I'd certainly get cracking on your own research.

[deleted-71588]

Do you value your sleep?

Way to ambitious a project for the time frame! Even a Wilbur and Orvil Wright type team working full time almost around the clock with a bicycle machine shop would have difficulties with this time frame.

The following is just a stream of ideas, so consider its worth, what you paid for it... (not much - the time to post and read the replies).

I'm trying to think of a good inexpensive source of DC motors in the 1/10 to 1/4 HP (horse power) range. If you had one, putting a sprocket on it combined with making a longer bicycle chain could work. If you mounted the bicycle and DC motor to a piece of 1/2" or thicker plywood so that the rear tire was off the ground and the pedals turned both the motor and the rear tire, you have almost everything you need. The only thing missing is a circuit to short out the motor windings to provide braking. You test the "rubber" brake pads on the existing bicycle braking system and use the motor back EMF and magnetic field as the electrical brake.

Even this would take a LOT more time than you think. You need to leave time to design and construct some experiments, gather the results, analyze and present them. Doing the work is only part of the job. Documenting and writing about it and coming up with a good presentation takes time too.

Better to scale it down even further. Do you have an "Erector" set?

The steel rods and brass gears with holes in them could be used to mount a piece of aluminum plate to a shaft. You could turn it with an electric drill with a friction coupling to get it up to speed and then do your braking experiments on the rotating aluminum disk.

Unless you already have powerful magnets, the time to acquire them will be a problem.

Time to go scrouging for things...

And the above all assumes you have a skilled Dad or Mom who is handy with tools and has a variety of them and who has the time and is willing to help. Don't underestimate the time it takes to setup and cleanup to leave your workspace acceptable to the rest of the family.

[Snake]

When it comes to help, my stepfather knows a shop that'll do most of of the non "child-friendly" bits such as wiring and woodwork.

What I think is most viable for the most visible results is to obtain a single speed small bike with a twelve to sixteen inch diameter disk. With the help of the shop, i should be able to lop off the front to modify it into a stand along with changing the seat to accommodate a person my age. I most probably can't use the sprocket and motor idea suggested by the previous poster, because I do not know much about the means of acquiring such motor or even being able to explain it with my very limited knowledge of electrical circuitry, and being able to call it "eddy currents". This all seems to wrap together in my head rather nicely.

An aluminum disk can most probably have holes drilled into it so screws(maybe?) can replace the wires on a bike wheel. I modify the brakes to accommodate the rubber and probably have magnets not associated with the brake system of the normal bike,but probably a friend with proper safety wear, to push two large neodymium magnets maybe a centimeter away form the wheel along with having the magnets covered in a substance able to keep them from breaking each other because they are very brittle. Or Just get one magnet.

For the board I push my experiments findings into theory and include tidbits about roller coasters braking, and the eventual cost of replacement of rubber brakes.

[deleted-71447]

Hi Snake,
Have your or your step dad explained to the shop what you want to build? Have you gotten an estimate from them of when they could be able to complete their work? If they are going to be able to do most of the work for you very quickly and cheaply, that's great - but I would be prepared to pursue some simpler alternatives, such as the scaled-down models that the experts have recommended. For example, here is an example of a eddy current brake that uses an old hard drive platter:
http://www.coolmagnetman.com/magalum.htm
Good luck!