Two Twirly Spikes?

LIM and magnetic brakes are actually conceptually close to each other. The difference is that LIMs use electromagnets that change state and magnetic brakes use fixed magnets.

LIM are basically a simulation of moving magnets. Simular to magnetic brakes inability to stop a train, trains can't move at the same rate as the magnetic field. The difference is called slip. With all factors equal, the more slip, the higher the force to a point. Simular to brakes in that the faster the train moves, the harder they brake.

For the launch, the force put on the train is directly proportional to the slip or how much the train is falling behind the motion of the magnetic field. The slower the train in relations to the field, the harder the push. There is a point where the force peaks out and drops if the slip is too great. The speed of the magnetic field is adjusted to give a constant slip to maintain a constant launch force.

Say you want a vertical brake with LIMs. Basically a launch run straight up. The train is under 1 g of acceleration towards the ground due to gravity so the LIM must have a force upwards that equals the force of gravity. Do this while the train is stopped and the train will remain in position.

If the LIMS on the spike are in steady state, you run into two problems. No magnetic field is induced into the plates untill the train rolls backwards. This obviously will not stop the train. Also the motors act like short circuits and generate incredible amounts of heat.

To produce a brake, the motors must be run upwards and at enough slip to cancel out the force from gravity. Each set of passengers weighs different amounts. This means that the slip required is different too. The LIMs must be able to push the train hard enough to hold the train in place and the train has to be fully into the LIMs. Otherwise the train will slip out. Timing is also critical. Too soon and the train might not stop, too late and the train will have more momentum that the LIMs can stop.

Also, there might be the problem that the LIMs can hold a train up to a certain weight. Go above that and they won't be able to stop the train.

It comes down to being hit or miss. I wouldn't be suprised if efforts to get it to work cease due to budget constraints or other problems.

Umm is it just me or was the actual answer never covered in that post?

Maybe since I heard the Peanuts teacher when I read it, it was, but I couldn't find it. ;)

I am 99% sure that the brakes are LIMs. I think, unlike the launch LIMs, these do not "pulse" and instead simply stay on to hold the train in place.

Geauga: http://www.geaugaguide.com/photos/photo.php?id=1019
http://www.themeparkreview.com/forum/files/gl-steelvenom007__small__358.jpg

The other SV: http://www.rcdb.com/ig1920.htm?picture=6
http://www.rcdb.com/ig1920.htm?picture=11

Remember that sound it makes when it stopped? That is the LIMs running. Besides, I dont think regular friction brakes would be strong enough to hold the whole train up. *** Edited 2/6/2007 10:22:09 PM UTC by Rider***

It's so much prettier painted blue and gold rather than red.

I personally think it's a mechanical brake. If it were a LIM brake, I wouldn't think you'd feel the train bump into whatever that is when it's back on it's small journey down when the brake locks after you go up the back spike the last time.

I could be wrong tho. ;) Does anyone know if the Mr Freeze @SFSTL uses LSM/LIMS to push the train up the spike?

i definatly know that vertical velocity's r mechanical. as for which one i like better,(straight or "twirly") i like them both equally for different reasons.

Loopy said:
Umm is it just me or was the actual answer never covered in that post?

Maybe since I heard the Peanuts teacher when I read it, it was, but I couldn't find it. ;)

I guess if you want a simple answer, yes, LIMs can be applied as a brake. The LIMS have the ability to push the train hard enough to do this. In fact, that is why they are used for a launch.

Rider said:
I am 99% sure that the brakes are LIMs. I think, unlike the launch LIMs, these do not "pulse" and instead simply stay on to hold the train in place.

By pulse, do you mean the slow motion jumping action that the train makes while moving in the station at low speed?

They're LIMs. You can hear them "scream" when they hold the train, and you can actually see them when you're stalled if you're in the front row.

Is there an impulse that actually holds the trains on the spikes? I find it to be highly improbable that those brakes are designed to hold the train, for two reasons:

1. There's absolutely no need for it.
2. It's a mechanical nightmare to imagine how that would play out.

Unless I am totally off my rocker, I can't imagine a scenario where it would be desirable to hold the train on the vertical spike. The brakes would be useful as a speed-check, to insure the train doesn't go flying into the stops, but to actually hold the train?

Yes, they do. I know the SV at ValleyFair does. Its for no more than a second, but there is a definite pause at the top of the last trip up the back spike.

Okay, in that scenario it makes more sense. I was getting the impression that the discussion was in regard to some sort of safety braking setup.

No. There is a brake at the top of the spike that does a quick stop when the train peaks. It actually surprised me the first time because I didn't know it was there and I was wondering what the heck was going on.

As far as I know, all of the Intamin impulses with a straight back spike have the brake up there.

I see. I assume that the pause is for entertainment purposes, correct?

Yep.

Were you?

Actually, it scares the Granholm out of me. Or at least it did the first couple times I rode because I didn't know what it was. Once I realized that the braking was supposed to happen, its actually pretty cool, especially when in the front row, because you hang for a second staring straight down.

Jump to Conclusions said:
By pulse, do you mean the slow motion jumping action that the train makes while moving in the station at low speed?

No, sorry for my funny wording. I mean how the motors switch between attracting and repelling (or north/south) in order to pull and then push the trains down the track.

How LIMs work: http://capital2.capital.edu/admin-staff/dalthoff/lim.html

In the verticle brake I believe it no longer "switches" (a better word) and instead uses an attractive force along the length of the train to hold it in place.

^ If you were speaking of Synchronous motors, you would be correct. Induction motors aren't push-pull.

The "holding brake" is really just a set of LIM stators firing in the opposite direction of the train (up) with equal force that kind of suspends it for 3/10 of a second or something like that.

If you pay close attention, you will notice the train kind of "stutter" forward and never really stop - it comes close enough that it counts, but you get the picture.

-Josh

Rider said:
In the verticle brake I believe it no longer "switches" (a better word) and instead uses an attractive force along the length of the train to hold it in place.

That is the condition I stated with steady state. DC current to the stators, or lack of switching means steady voltage or steady state.

Jump to Conclusions said:
If the LIMS on the spike are in steady state, you run into two problems. No magnetic field is induced into the plates untill the train rolls backwards. This obviously will not stop the train. Also the motors act like short circuits and generate incredible amounts of heat.

LIMs have to induce a current into the reaction plate. If the current stays constant as in steady state or DC voltage, no induction takes place and therefore no current is induced. If there is no current there is no force. What the LIMs will do is act like magnetic brakes... poorly. The train will quickly slide out of them.

Induction is needed so the motors are ran upwards. Think of magnetic brakes attached to a conveyor belt moving upwards. The speed of the conveyor belt will control the speed of the train. The faster it runs, the more force it puts on the train.

The optimal speed is the one that will hold the train in place. Too fast and the train will move up, too slow and the train will slide down. The speed of the conveyor belt is the speed of the field of the magnets on the conveyor belt. LIMs operate by simulating this field. They produce a moving field.

The train is just trying to keep up with the field. If the field is moving upwards, the train wants to keep up with it but slips behind the field. If the field is going too slow, then the train will go down. If the field is going too fast, then the train will move up. The idea is to make the field go up at the right speed to keep the train in position. It's impossible to get it perfect, but not too difficult to get it close.

With launching the train, the idea is also to control the speed of the train. Instead of holding it still, the idea is to get it moving at a specific speed. The field has to move at a faster rate than the train, but the train will follow.

One fact that I have left out so far is how is the field speed changed. The answer is frequency. The power company sents 60hz current. We need variable frequency. The higher the frequency, the faster the field travels.

Drives are devices that operate motors. AC inverter drives chop up the power AC source and rectify it into DC voltage. This DC voltage is then fed into a special bridge with a bunch of semiconductor switches. These swtich at a high frequency and form an AC signal that looks simular to the AC that the power company sends. The difference is that we have full control over the voltage and frequency. The high pitch noise that the motors make are icaused by the inverters making their own AC waveform.