Tuesday, December 3, 2002 6:28 PM
I have been doing some research, and I had an idea. Could you build a LIM? I have this idea, if you make 2 coils with wire and a nail for say, and hook them to a power source. Then put them in a box shaped like a real LIM box? When the power is turned on, and you run say aluminum through the magnetic fields produced by the coils, would that work in propelling a coaster?
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Tuesday, December 3, 2002 6:52 PM

Well, that'll only work if the target that you're running through the field is ferrous (I think? Rideman?). i.e. it's iron

In terms of the actual E&M, it will induce a polarization in the target and draw it towards the middle of the inductor. However, once the target is past the midpoint of the inductor, the field will be pulling the target in the opposite direction: back to middle. Thus, unless you get really good at flipping the switch at the right time, this won't really help for anything but a brake.

For a more detailed explanation of LIM's check out RideMan's page (whose URL escapes me). You really need sensors to control the LIM's if you want to be efficient at all.

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Tuesday, December 3, 2002 7:54 PM
Flick the switch off when the item you're propelling reaches the magnets, and it'll work as one set of magnets. You'll need some contact or optical sensors and maybe a nice mini-PLC if you want a whole series of LIM magnets that fire in succession.

*** This post was edited by auscoasterman on 12/4/2002. ***

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Tuesday, December 3, 2002 8:13 PM

One LIM easy to make

More then one gets testy as you really have no way to fire them in succesion without some major tecnology going on.

A LIM is essesntially the same motor you have in your ceiling fan, just flat. Instead of a comutator in between magnets its the train between the magnets. Quite simple and ingenious actually.

I think I am gonna have to try my hand at making a HO scale LIM myself.

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Coming in 2003-The Spawn Of Magnum!

I AM WITTY!

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Tuesday, December 3, 2002 8:58 PM

Absolutely you could build a LIM. A mini-PLC isn't really necessary you could do it with a $4 microcontroller. They're a bit more complicated than two nail and wire electromagnets but certainly not out of the question. Realistically a LIM isn't any different from any other induction motor, except that it is commutated electronically. And of course it's not in a circle. You really don't even need electronic commutation except i don't think you have 3 phase power handy and i don't want to suggest you make a circuit that runs off 230 volt 3 phase even if you had it.

If you want to do it easily and slowly just get a basic stamp for control (www.parallax.com) and some MOSFETs to drive your coils. Get some ~20 guage magnet wire from radio shack. Probably easiest to use a 12v gell cell battery if you have one or a radio controlled car battery if you don't. the basic stamp is key; it's quite a bit more expensive than a pure microcontroller setup, and really slow, but it's also by far the easiest way to get started in microcontrollers.

As usual Rideman's explanation is excellent. The only thing i can add if you're looking to make one are the following. This is assuming you want something that functions, not necessarily something especially efficient or high powered. Certainly not something fast if you're using a basic stamp for control. But it will move.

First off, i'll say make a LSM. they're easier to understand and the commutation isn't that bad.

You'll want a multiple of three coils. I'd say six is a good number to start with. Certainly you'll want less coils than half the IO pins on your controller. I don't remember offhand how many pin that is on a basic stamp, but i'm sure it's at least 12 for the BS2. Get six button switches. Ideally these will be switches that take almost no force to depress and travel say 1/8th of an inch. position these between your coils. The sixth would go at the end of the assembly. Make some sort of striker on your vehicle such that the button depresses when the magnet on the vehicle is directly over the coil. Wire these buttons to the basic stamp as inputs. Get some logic level FETs. They're about a buck apiece from digikey. You want logic level N channel. Wire these to control your coil, with the gates connected to six output pins from the stamp.

The program would go something like this. Start with the vehicle behind the first coil. when you press the start button, have the first coil energise and the rest of the coils off. when the first button is pressed, have the first coil switch off and the second coil switch on, and so on until the last button is pressed. The basic stamp has a button command that is handy here. This will give you a very very basic variable frequency drive and with proper vehicle magnet and electromagnet strengths, it will fire. It's very inefficient, and only kinda a true AC motor, but it will fire and i could cook one up in an evening given the parts, so you can do it.

There are much better ways to build, sense and program a linear motor, but this is the easiest i could think of.

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Tuesday, December 3, 2002 9:03 PM

MagnumForce if you mean one coil, that isn't a motor it is a solenoid. Alternatively it's a coil gun depending on how you set it up. It doesn't take "major technology" to switch the field, just a bit of electronics. $10 in parts.

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--Proud member of the "More brains than common sense" club.

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Wednesday, December 4, 2002 10:58 AM

One note here. The fin on a true LIM is not magnetic. In fact, making it of a magnetic material would hurt performance. The important characteristic of the fin is electrical conductivity to maximize the "induced" currents in the fin. The fins on full size coasters are all aluminum as far as I know, though copper would also work. Actually silver would be good, but you can imagine why they don't use silver.

A magnetic material is used to back the aluminum induction fin when a one sided LIM is built, but I've never actually seen one

An LSM probably would be better for a home build.

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Wednesday, December 4, 2002 11:19 AM
How does a LSM even work. I know what it is, but I dont understand how it works. And Comatose, could you give me a website to go to to order those parts you told about? I was also kind of confused on how you told to make it, but i will have to read it a few more times
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Wednesday, December 4, 2002 11:39 AM
Comatose. No actually I mean making a motor flat instead of round basically. A solenoid would involve more of an electric switch type thing. Correct?

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Coming in 2003-The Spawn Of Magnum!

I AM WITTY!

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Wednesday, December 4, 2002 11:42 AM

Whats Rideman's website?

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Wednesday, December 4, 2002 12:14 PM

http://capital2.capital.edu/admin-staff/dalthoff/

Bookmark it. You won't be sorry.

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Wednesday, December 4, 2002 12:27 PM
i know i'm no good with magnets..... but what if you got a single-pole magnet ( lets say.. a (-) ). Then you set up normal double-poled magnets along the launch track so the (+) would be facing the car, and the (-) would be on the other side. Now what i think would happen is the negative magnet ( one poled ) would get pulled towards the opposite, positive side of the other magnet, once it reach the half-way point... it is suddenly negative to negative. That would mean they woudl repel. If you set up a line of a bunch of double-poled magnets, maybe it would work?? Does this make sense? if it doesnt, i can try to draw a diagram.

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Women was god's second mistake.

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Wednesday, December 4, 2002 12:29 PM
It must be down right now, its not coming up
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Wednesday, December 4, 2002 12:41 PM
I kindve get it, but if its not any trouble, could you draw the diargram
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Wednesday, December 4, 2002 1:51 PM

If you want, just check out what CPBound said here

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I am not the real Chris Sawyer...Or am I?...No.

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Wednesday, December 4, 2002 2:52 PM

Magnumforce if you make the motor flat instead of round how would you commutate it? unless you're postulating a brushed linear motor... that'd work but be kinda funky

Solenoids are a type of linear actuator. they are NOT a switch, except that they're often used to actuate switches.

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Wednesday, December 4, 2002 2:56 PM

DLDude13 said:
i know i'm no good with magnets..... but what if you got a single-pole magnet ( lets say.. a (-) ).


If you got a single-pole magnet (called a magnetic monopole), it'd also probably come with a Nobel prize. Magnets have only been discovered in nature as bipoles.

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

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Wednesday, December 4, 2002 3:00 PM
What makes LIM's shriek like they do?

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Säubern Sie mit Milch?

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Thursday, December 5, 2002 5:38 AM

http://uploader.axsstudios.com/images/Bipoiler.jpg

Theres a diagram of what i mean. Thanks Andy for pointing out my supidity, but i fixed it in the diagram. So do you think this would work... provided you gave the car a little shove at the beginning?

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Women was god's second mistake.

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Thursday, December 5, 2002 6:51 AM

Nope. Still wouldn't work. The problem is that the negative and positive sides on the moving magnet are relatively close, so the difference in force attracting the close end and the force repelling the far end is not that great. There is a small difference of force, though. However, it's exactly cancelled out (conservation of energy) by the large retarding force when the fixed magnets are in between the two poles of the moving magnet. You could get a weird velocity curve, but your exit velocity would be the same as your entrance velocity (conservation of energy again) in the frictionless case.

Sorry, but you're going to need to add some power if you want to speed something up (again,conservation of energy).

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*** This post was edited by ApolloAndy on 12/5/2002. ***

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