Magnetic breaks - why can't they stop?

Why are magnetic brakes NOT able to completely stop a roller coaster train, or drop ride?

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Intelligence is a God given gift: Know how to use it.

http://www.magnetarcorp.com/

They will stop completly, but then drift.

Rideman?

They stop Xcel. They stop the train then the fins on the track drop and the train starts again. I think.

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"I took the highway to the danger zone"

I think they can't completely stop it because if they do then it'll start to push the vehicle backwards. So you just hafta find that point to slow it down, then continue braking with pinch.

NorCal Kid1 -

Actually, the brake run on Xcelerator does not have the snap-down steel brake fins until the flat section right before the turn into the station, but that is rarely used, only for placing one of the trains onto the transfer. The inclined brake run slows the train down to a slow speed and the train is heavy enough to "slide" off the incline.

Isn't it so that the braking gets done by electromagentic fields caused by the passing of the train (eddy current brake)?
So when the train has no speed, there's no braking because the magentic fields are not induced... That might be why they don't work as effectively on low speeds, and thus it might be difficult for such a brake to stop a train completely.

The web site that bigkirby provided explains that magnetic brakes can stop a ride, they just can't hold the train/vehicle in place. Understand that I know very little about magnets, so this is just speculation, but here's my next question: Let's say that at the end of Millennium Force's magnetic brake run, Magnetarcorp and Cedar Point installed one more set of brakes. These brakes would have the opposite polarity of th fins on the train, so they would be attracted to each other. This would hold the train in place, similar to putting two refrigerator magnets together. The brake would then be released by moving it to the side, and the train would move forward. Is this possible?

EDIT: I just noticed this, but why/how was the topic name of this thread changed?

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Intelligence is a God given gift: Know how to use it.

*** This post was edited by CoasterKrazy on 1/11/2003. ***

Heres how Knotts works, start to finish. The ride op says dispatch, you roll backwards when the Pre Staged row of lights turn on, stop when it says staged, then the count down, then the launch. As you pass each section of lowered copper fins, they raise in case of a misfire/rollback so the train will not crash into the other one. You hit the standard intamin flat track, and permanently raised copper fins are stuck out. Then you hit the box track, which has more lowerable copper fins, but they are up as you hit them, but lower as you pass them, and then raise for the next launch. So Kraxelridah, get your stuff straightened out. Then the box track flattens out, but the copper fins lower usually before you hit them, as to not go 3 MPH, but rather about 8mph. If they want to stop the train on the transfer track, all the copper fins would stay up, and the train would get stopped by friction tires on the transfer track. Then you get to the turnaround, which is all friction tires, used to propel you and stop you. http://www.twistedrails.com/kbf/apr25-06.shtml

On S:RoS @ SFA, they completely stop the train every time. If they didnt, you would drift right into the next train.

Also, the trains dont necessairly stop the train completely all the time, simply because it can move onto the next block.

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#1-MF #2-Apollo's Chariot #3-S:RoS

Coasters Ridden: 42

Those would be tires that do that.

That is exactly why the tires on S:RoS are so bald.

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SFNE Central- Online Six Flags New England Resource
Devoted Intamin Lover for Life!

CoasterKrazy said:
"Let's say that at the end of Millennium Force's magnetic brake run, Magnetarcorp and Cedar Point installed one more set of brakes. These brakes would have the opposite polarity of th fins on the train, so they would be attracted to each other. This would hold the train in place, similar to putting two refrigerator magnets together.

I don't think polarity matters at all here.
The magentic brakes used on coasters are eddy current brakes. That means that as the train goes past the fins of the brake, permanent magnets attached to the train create eddy currents (circular flows of electrons) inside the fins. These result in magnetic fields that in turn hold back the train.
An physical experiment setup can be seen on this page:
http://demoroom.physics.ncsu.edu/html/demos/192.html
Image the fins to be the rotating disc and the permanent magnet to be located in the train.

If the disc doesn't turn, not eddy current gets induced, so no braking occurs: That's why train gets never stopped completely.

Magnetic brakes cannot completely stop a ride, though they can come very close. The Magnetar brakes have an auxiliary mechanical component to provide the final stopping and holding.

Superman had it pretty much right. As the conductive fins pass through the fixed magnets the varying magnetic fields from the fixed magnets induce electrical currents in the fins which in turn create a magnetic field associated with the current that reacts with the field from the fixed magnets. If the train is not in motion, there is no induced current therefore no magnetic field, therefore no braking. The force is the greatest when the ride is moving the fastest, as it slows the force becomes less and less until it reaches zero at stop. This isn't the ideal way to slow a train, so the spacing and strength of the magnets and the gap between the magnets are adjusted to further regulate the breaking. This results in the breaking curves that you see at Magnetar's web site. Braking starts a little slowly then increases as riders adjust. It is held constant by the design of the brakes until the speed becomes very low at which point the magnetic brakes are no longer very effective.

coasterdude04 said:

On S:RoS @ SFA, they completely stop the train every time. If they didnt, you would drift right into the next train.
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#1-MF #2-Apollo's Chariot #3-S:RoS
Coasters Ridden: 42

Actually, on S:ROS when you hit the breakes, if you look closeley after you "stop", you can actually see the train moving VERY slowly forward. Slow enough to only notice it if you are on the train and looking down at the brake callipars on the side.

The neat thing about magnetic brakes is that the braking force is proportional to the speed of the train. It basically means that once adjusted, assuming that the train and magnet grouping is long enough, the train will always come out of the brakes at the same speed, regardless of how much the train weighs or how fast it was going when it entered the brake or what the weather conditions are.

But the basic Physics as outlined here goes back to the elementary concept: When you move a conductor through a magnetic field, you induce an electrical current in the conductor. When an electrical current moves through a conductor, it generates a magnetic field. The key, though, is motion. If there is no relative motion between the conductor and the magnetic field, there is no induced field. So when the coaster train stops, the braking force drops to zero.

I think we just went through this discussion in another thread talking about linear motors!

--Dave Althoff, Jr.

With magnetic brakes, would it be at all possible to harness that lost engery and use to to power launches / lift hills / mechanical brakes / etc.?

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Intelligence is a God given gift: Know how to use it.

I wouldn't think so because the energy is generated right in between the fin and caliper, right?

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SFNE Central- Online Six Flags New England Resource
Devoted Intamin Lover for Life!

Um...I would guess that the energy is lost in the electrical resistance in the fin, but I really have no idea. Where else would it go?

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Be polite and ignore the idiots. - rollergator
You must be this dumb to ride Viper. -SFGAdv.

I have noticed at S:ROS@SFDL the train stops all the way. One time i was in line and the train hit the brakes, while the other train was loading and it took the ride ops a very long time to load the next train.

I remember sttd to my friend "it sure is taking a long time to load", and if anyone's ridden this version of S:ROS they know that the que is right next to the brakes, so close you can talk to the people on the train.

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Someone Who Hopes Their Homepark wakes up and smells the coffee!

I thought they can't stop because they don't create sliding friction between the car and the brakes. Just an idea!

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Mike T.
Fly with the man of steel in 2003!