h a l f b a k e r yYeah, I wish it made more sense too.
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As people know, car's brakes work by clamping 2 bits of friction materials onto the spinning disc that is connect to the wheel.thus the pads need replacing once in a while because they wear out.
So. I propose a magnetic braking system. This concept can be easily seen by spinning a metal gyroscope, then
putting a strong magnet near it, the spinning gyro virtually stops instantly, without touching the magnet. This works thru what's known as "eddy currents" induced by the magnetic field.
To put this into a car, electromagnets will replace the permenant magnets. And a secondary traditional brake is also present in emergencies. This idea not being cost effective, it could also be used as regenerative braking for hybrid cars, as this is able to generate small amounts of current.
The main problem lies in the fact that there'll be a need for 2 brakes on each disc instead of 1. Otherwise this is a much better version of brakes on cars.
Eddy Current Braking
http://www.pa.msu.e...index_e/3/E3_01.htm
An enormous animated GIF showing the phenomenon in action. Hope you have a T1 line . . . [bristolz, May 19 2002, last modified Oct 06 2004]
Electromagnetic Braking
http://www.a-car.co...d/messages/643.html
"Electromagnetic brakes do exist. They are of two types. First is mechanical type and the other is Eddy Current type." [bristolz, May 19 2002, last modified Oct 06 2004]
(?) Torspec Eddy Current Brakes
http://www.torspec....ec_brakes2_page.htm
Commercial (non-automotive) eddy braking systems. From the "learn something new everyday department": I guess eddy brakes form the foundation of automotive dynamometers. [bristolz, May 19 2002, last modified Oct 06 2004]
Amazing Secrets of the Third Rail
http://www.nytimes....yregion/30TUNN.html
NY Times article (free registration required) about reclaiming the energy from trains as they brake in a similar manner. [krelnik, Oct 16 2002, last modified Oct 06 2004]
[link]
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//a secondary traditional brake is also present in emergencies// |
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what counts as an emergency? The sudden cut-in of the brakes in front of, say, a set of traffic lights might actually cause an accident.. |
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I note that you say "virtually stops instantly" with regards to the stopping effect of the magnet on a gryoscope. Hope you've got some form of whip-lash prevention installed in that there automible sonny. |
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Electromagnetic braking does have some advantages over friction braking. If the power produced is stored, it provides "free" energy. Even if it is not stored, it may be easier to dissipate the power as heat somewhere other than the wheels. As a final advantage, EM braking has inherent "anti-lock" characteristics. |
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The biggest difficulties with such a thing are: (1) incorporating a proportional braking control at reasonable cost; (2) designing the braking system to be robust in case of electrical-system failure; (3) the need for a proportionally-controlled mechanical braking system to bring a vehicle to a complete stop (on any sort of hill, an EM braking system--unless actively powered--will be unable to stop the vehicle completely; the mechanical supplemental braking system must be proportionally controlled because a sudden stop from even 1mph (1.6kph) would produce a very annoying jerk. |
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should have made it more clear..
these wouldn't be used for sudden stopping, the gyro stopped quickly because it was small.
these would mainly be used for light braking and for some degree of deceleration. and hey. 1600kg for a car?? i don't think yank tanks would have anything like this, i'm looking at more a hybrid car, 900kg type.
the mechanical "emergency" brake should be a supplementary brake, to allow "harder" braking. |
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but hey. even personally i'd stick with the good ol' handbrake for the corners. |
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It seems that you are missing the full effect of such systems. |
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As braking is in fact the opposite of accelerating an electric car could theoretically, with use of a combined dynamo/electric motor unit (In their purest forms they are the same thing) which uses the unit for both propulsion & braking via the "dynamo effect". |
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Such a system would only require energy input to equal the losses(/gains) from inefficiency (e.g. The Motor/Dynamo itself, friction, wind resistance & nett gradient). So if a vehicle was 90% efficient & it took say 400,000 watts to go 100,000 km then the cost would be 1/10th this or 40,000 watts (Don't you dare take these figures as anything other than illustrative). |
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How is the state of such art ? |
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Wocca is right on. In the electric car, you could reclaim the kinetic energy of the car and generate electricity from the turning wheels, recharging the battery. |
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Probably in something like a train it would work even better. The energy harvest mechanism could even be external, since trains stop at predictable places. One could run the lights at the train stration off the power reclaimed from the arriving trains. |
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[bungston] The New York subway system does precisely what you just described, using huge flywheels to soak up energy piped back into the rails by trains as they stop. They then pipe it back into the system as electricity when needed. See link. |
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the faster the car goes, the quicker the deceleration.
a car breaking from 70mph to 50 mph would take, lets say 2 seconds. while the same car breaking from 50 to 30 would take 4 seconds* |
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*not actual tested results. |
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Almost all electric cars (and hybrids) do exactly this ("regenerative braking"). Isn't this monstrously Baked? |
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This will only partially work, perhaps as tertiary braking. Don't forget, eddy braking needs the conductor to move relative to the magnetic field, i.e., it is dysfunctional if the car is at rest. Now, this would pose a problem if you were on a slope, cos you'd keep rolling back. |
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Yes, and in fact in almost all implementations, regenerative magnetic braking is used in conjunction with ordinary friction brakes. Nothing new here. |
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i have finished my courswork on electromagnet braking. |
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it has shown me something amazing.
these are actual test results, using a DC supply of 0.1V, 3A going through each 240 turn electromagnets. |
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to stop the disk using this method, took 3m41. |
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now i further extended my project by setting up the electromagnets out of phase, using 4 capactors on one of the electromagnets. this time it was AC, 6v, 1.5A throgh one, and 3A through the other, and the results were stagering. |
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the disk stoped this time in 40 seconds!!! which is over 3 minutes faster, using the same power supply. the added advantage of having one of tem out of phase was that it stoped the wheel much faster when it was going slowly. so it could theoritaclly stop a slow moving car down a hill. |
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Yes egnor, this subject is monstrously baked to the point of cremation.
Neildm, if the vehicle had regenerative alternators fitted on each wheel (usually the case) and a DC voltage were applied to these alternators they would stay put as long as the current remained - DC makes an AC device stay put. This has been done in industry (e.g steelworks) for decades on overhead cranes and machinery for emergency braking. |
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Being an inquistively minded bloke a few months back, say about september 2002, after reading this website i began planning a project to investigate the potential applications of electromagnetic raking using eddy current braking as part of my physics A level. Well about 5 moths later i've just finished the project. Using an electromagnet positioned over the edge of a 30cm diameter rotating disc I ivestigated how the disc decelerates form various initial speeds when different currents are applied across the electromagnet. while the results are by no means perfect i have still been able to draw several cocnlusions.
The fisrt is that the rate of deceleration is based on both the current in the electromagnet and the velocity at which the disc is rotating, i.e. for a given current in the electromagnet the deceleration is not constant, it decreases as the velocity decreases. This is not entirely unexpected as the EMF generated in the disc and hence the size of the magnetic field generated is dependant on the amount of flux cut per second whcih is proportional to the velocity, i.e. the faster the disc rotates the more flux is cut. This is important because it is the magnetic field generated in the disc and its interaction with the origional magnetic field in the elctromagnet that causes the dceleration. This means therefore that to provide a constant dceleration the current in the electromagnet must be increased. However by using an on board computer this would be achievable and has been proved to work by my results which allow for the current to be set automatically to provide a range of decelations at a range of different velocities. By expanding the experiment i would be able to provide such data to aloow a car to stop at any speed safely and reliably, working as a true brake system. |
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Id be interested to see how OnTheLimit's experimnet worked cos mine manged to slow the disc from approximately 30mph to a stop in forty seconds using a 600 turn solenoid a large horse shoe iron core and a current of 4 A with a voltage of 12V. |
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ill send any one a copy of the final writeup by email if they want it, email me at edward.farnell@btinternet.com |
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Trains use a system like this called "dynamic braking". Only the power created is pushed through huge resistors on the roof, and disspated away as heat. |
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I will be hosting my project esle where very soon, i just need to go home and find it. Sorry to thos people who have been dissappointed, Ive been very busy at uni. Anyhow, new site with files coming soon. |
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Good News, my project will be available at http://www.chu.cam.ac.uk/~ef242 from the 19th April onwards, happy reading. Ed |
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P.S. Dont forget to write back with any news you have. |
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[+] because i was thinking of this exact same thing today and was going to post it but saw yours |
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What are then those thingies the trucks have on the back axle, called electromagnetic brakes?. With enormous double walled, forced air cooled discs placed each side of a mother of an electromagnet?.
A birdie told me they are used to brake when going downhill, not to stop to a complete, inmobile, total stop. |
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