MagLev C

[Flavorflav]

Remember also that Earnshaw's theorem showed that stable levitation with permanent magnets is impossible. You might be able to make the fields form a saddle, but I doubt that it would be worth the effort under this year's rules.

[joeyjoejoe]

Considering rule 4c regarding side rail magnets being allowed, I'd get rid of the bearings, add magnets to the sides of the car and track, and get rid of the friction. Then do the calibration work.

We have tried this and had no luck. In fact, I don't know how the makers of actual maglev trains do it, but it seems impossible to have the car not touch the side rails.

EDIT: Oops! posted before reading the last post. Apparently, this Earnshaw person has proven what we have seen in the work room.

[iwonder]

http://math.ucr.edu/home/baez/physics/G ... ation.html

Looks like they can use active cancelation or diamagnetic properties of super conductors to obtain stable levitation.

[JimY]

Considering rule 4c regarding side rail magnets being allowed, I'd get rid of the bearings, add magnets to the sides of the car and track, and get rid of the friction. Then do the calibration work.

We have tried this and had no luck. In fact, I don't know how the makers of actual maglev trains do it, but it seems impossible to have the car not touch the side rails.

EDIT: Oops! posted before reading the last post. Apparently, this Earnshaw person has proven what we have seen in the work room.

I don't know if Earnshaw's theorem applies here. It seems to be for an object levitating on a flat surface without moving around, hence stable or static.

If you have side rails to cradle the car while at rest such that it isn't touching anything, you are still subject to gravity. So, if the car moves with the motor off, the magnets aren't level enough. My team hasn't started yet, so we haven't tried it. Another thought is that you might need a certain amount of vertical separation between the side rail magnets and the track magnets. Also, the strength of side rail magnets can be much less than the track magnets. You might need to find the right combination of parameters like these for it to work.

After a bit of work on the subject, I now see the inherent instability issue being discussed and have found no arrangement of side magnets that alleviate it, either on the track, the car, or both. No surprise in hindsight. If anyone finds an arrangement that does the job, I salute you.

[cnapun]

Could someone please explain why the online instructions to build a track say to have opposite polarity magnets on the opposite sides?

[iwonder]

We had a lot of discussion about this last year, and the general consensus was that it didn't really matter as long as you had the vehicle set up to levitate. If you put the same polarity facing up it's also more convenient because you won't have to switch around magnets to change the direction of the vehicle.

[chalker]

Could someone please explain why the online instructions to build a track say to have opposite polarity magnets on the opposite sides?

Mainly due to cost.. that way you can buy 1 set of normal magnets (with a north and south side), and use them on the track. There's nothing preventing you from doing all north or all south, but it typically will cost a little more.

[iwonder]

Could someone please explain why the online instructions to build a track say to have opposite polarity magnets on the opposite sides?

Mainly due to cost.. that way you can buy 1 set of normal magnets (with a north and south side), and use them on the track. There's nothing preventing you from doing all north or all south, but it typically will cost a little more.

I don't see how it costs more? Wouldn't you need magnets for both sides of the track, so you could just flip them over on one rail and have all the same polarity facing up?

[chalker]

I don't see how it costs more? Wouldn't you need magnets for both sides of the track, so you could just flip them over on one rail and have all the same polarity facing up?

No, there are 2 types of magnets people typically use for tracks:

1. Magnetic tape. These come in 2 kinds.. the cheaper run of the mill halbach array kind (http://en.wikipedia.org/wiki/Halbach_array) which doesn't really work for maglev, and the more expensive kinds that has true north / south on the entire face. This kind is typically sold in a matching pair, with adhesive or sticky stuff on the one face of each part of the pair. Thus you can't really 'flip it over' since there is adhesive covering the other side.

2. Bar magnets. Some tracks have lots of rows of bar magnets laid down the length. Since one end is N and the other is S, if you get a long enough bar magnet you can just use them like railroad ties. Obviously 'flipping them over' won't do anything since they are standard bar magnets. If you want to have the same polarity, you need to get shorted bar magnets and put 2 per row (but technically then you actually have 4 magnetic rails (N-S-S-N).

[iwonder]

Ahh, my bad. We got the Pitsco tracks last year for Maglev and I guess they were lazy and decided to make us put the adhesive down ourselves And I've never seen a track with magnets like railroad ties but that makes sense now that you mention it.