LIM

i always thought that you just created an electromagnet, and run the aluminum through it. then the aluminum would induce the current, and try and keep up with the current. DLDude13, could you explain to me how your diagram is supposed to work. I am a little confused.

The theory was that the moving (vertical) magnet would attract until it passed each group of fixed (horizontal) magents and then repel. On the surface, this seems like it would get the vertical magnet going pretty well. However, as I explained, it doesn't work.

What're LIM fins made of anyway?

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

Usually a LIM fin is aluminum.

Also i would like to remind people that LIMS and LSMs are completely two seperate things. LIMS produce electro-motion. The stator creates an AC field that induces current to the reaction plate(fin).

-----------------
So you believe that you are studying us, then kindly explain why you are the ones trapped in your seats.

For power, could i use a model train controller, that has the forward and reverse, and the different power levels on it? I think for my science project I am going to build a short track, and have a car run on it, powered by LIMs, and see if different metals that run through the LIM change velocity.

For a small load, I'd think you could build a single-phase LIM using two sets of coils, and a single-phase AC power supply. How about this: Adapt a short piece of model railroad track to carry a car a short distance down a hill to a flat launch track. The launch track features a series of metal plates with an aluminum top plate over a steel backing plate down the middle of the track.

On the bottom of the car you have a series of coils positioned to interact with the reaction plate down the middle of the track. These coils are powered by pick-up shoes (or steel wheels) in contact with the track rails. Connect an AC power supply to the rails, and let it go. With any luck, the initial energy from the slight downhill should make sure it goes in the proper direction. It might not be the most efficient LIM around, but it ought to work...!

--Dave Althoff, Jr.: http://capital2.capital.edu/admin-staff/dalthoff
Who, he confesses, has never tried building one

The more i think about it the more i think that for the purposes of launching a small model or jsut gee-whiz factor, a BRUSHED LSM would be the easiest to make. you'd need a pair of carbon (or even just metal wiper) brushes, and contact strips that coincided with the electromagnets. These would turn on the magnet they were next to when the contact strips touched them. Next you'd need to position the strips somewhat ahead of the magnet, on a boom of some sort. The timing advance would have to be arrived at empirically, but a neutral timing of half the coil distance would be a good starting spot. With neutral timing it'd be reversible as well.

I think if i still have any brain power after my final paper i'm finishing tonight and my dynamics final tomorrow i'll try my hand at making one.

Dave: I love the idea of a single phase LIM, should work Pity none of us have three phase power to our homes, it's amazing how much cheaper 3 phase motors are. Easier to build too.

How about this: Get yourself a single-phase motor and a three phase motor and mount both on a solid surface. Connect the output shafts together. Plug the single-phase motor into a wall outlet. Connect the power leads of the 3-phase motor to your 3-phase science project. Not a cheap way to do it, but it gets you 3-phase power... :)

A single-phase LIM would certainly work, the only problem is that with a single-phase motor you can't necessarily guarantee the direction of travel. But if you start the motor by giving it a shove (as you did with that rotary motor you built in high-school Physics class) that problem goes away.

For a brushed LSM, you can put the brushes wherever you want; just make sure the busbar is aligned properly... :)

--Dave Althoff, Jr.

Comatose, could you draw me a picture of what you are saying so I can understand it a little better? I would really Appreciate it. I can tell you when I am thanking people for help on my project, everyone at coasterbuzz will get a thanks!

Rideman, could you if you have the time draw me a simple picture of how i could build a simple LIM. for my science project, i am going to test what conductors are best for speed with my makeshift LIM. i would really appreciate the picture. thanks!

Hey guys, i dont mean to get annoying, and tell me if i am please, im still new here, so i dont know. But could anyone out there who could draw me a picture of what comatose or rideman is describing, sort've a diagram i could use when i construct these. i want to get a start on my science project as soon as possible. thanks

The (Edit) button between the (Info) and (Quote) buttons will be very helpful in the future, I can promise you that. :)

-----------------
- John
I got a B&M T-shirt!

Hey

It's finals week so time for me is kind of catch-as-catch-can. By the weekend i'll be done, by monday i promise you i'll have a diagram if i'm lazy or a video if i get productive

Not a bad idea for a phase convertor,Rideman.It wouldn't be real efficient, but it would work. Pick the motors up used it might not cost that much, especially if they're fractional hp.

Just thought i'd jump in here and add an update to my brushed LSM idea. I tried it today, and it took about 2 hours to get working. By working i mean travelling from one side of the motor to the other on its own power. Of course, it was a mega-super-ghetto job , but it's doable. I used about 25 turns of 26 gauge wire around seven nails (glued together for a stick nailgun) and four coils. For the magnet i used a circular magnet i found on my fridge. I used a 6v gell cell for power. My coil spacing was 3/4ths of an inch on center. The track was a C made of 1/16th inch balsa. I stuck the whole thing into pink foam.

This is a very bad design. It works for the "whee it went three inches" metric but not much else. For one, for 6v 25 turns of wire is not sufficient. Or maybe if the coils weren't insulated in the foam. The coils were .3 ohms each and so they drew about fifteen amps of current. That's 67 watts of heat dissipated from each coil. Needless to say i blistered some insulation. If you're going to do this for real go to radio shack and get some enameled magnet wire. I'd say about 100 turns of #28 or so would be about right. Plan on using a battery or power supply that can source at least a couple amps. Alkalines are iffy. Small alkalines are right out.

For brushes i just used #14 stranded wire stripped. It made impressive sparks, but life before i had to reset the brushes was about five trips, and it took a LOT of twiddling with the brushes after they burned out to get it owrking properly again. Carbon brushes are the way to go if you're going brushed.

That said, I'm not going brushed for the next version. It's jsut too much twiddling for too little results.

So my next design involves mosfets to switch the power and probably optical sensors to detect the car. Depends on how many phototransistors i can scrounge from my parts box. I also ordered some hall sensors, so if they come first i may use them. I'll probably run at 12v and try to keep the coil amperage down to two amps, which will play well with the 3 amp mosfet switch ICs i found laying around. better cores are a necessity, though I'm not sure what i'll use for that yet. Maybe I'll go into the machine shop and make something properly. Maybe

cylindrical magnets are not good at all, they mesh pretty poorly with roughly rectangular coils. Moving the coils closer together resuted in interesting behavior where the magnet would not move if the next coil was activated whereas it would move if the coil two away was. Coil spacing for the round magnet seemed best about 3/4ths inch. one inch was too much, the magnet didn't really move. half inch was too little as descibed above. The magnet is a little more than 1 inch in diameter. Better would be a neyodium bar magnet magnetized in the cross direction. Sadly I don't have one.

So in short. Brushed LSMs work. The brushes are a pain to jury-rig. Circular magnets work, but not particularly well. Get your resistance above an ohm or so so as to not cook things. I'll report on how the brushless LSM works sometime this weekend. Or maybe monday.

*** This post was edited by Comatose on 12/12/2002. ***

Comatose, how did your finals go? If you have time, could you post a diagram or pictures?

Sorry to bring abck up an old subject, but Rideman, your expertise is needed. I am doing your train track idea for my LIM, and for the aluminum down the center, i am using some old aluminum siding. Now, are there any things you would like to recomend for me?

Dave: I read your explanation on your site (again, for, like the 5th time) and I think I finally got it. However, in the model train example you've made, won't the induction in the plates slow the train down instead of speeding it up? If the coil induces a current in the plate, the plate will be just behind the coil, which will pull it against the direction of movement, no?

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

You could get reliable direction for single phase LIM, but you would need starting coils and/or a capacitor start which makes things even more complex. Overall I would thing that an LSM would be simpler for model.

Jim: The way to get reliable direction in a single phase LIM is to have the reaction plate in motion before it gets to the coils. That way you can avoid the need for starting coils. Ideally, you have a gravity start, followed by a LIM launch. To insure that the LIM is doing the work, have the launch track run uphill. So you start by rolling downhill, then cruise uphill under LIM power.

My suggestion earlier was to put the coils on the bottom of a vehicle and the reaction plate in the middle of the track, and power the coils by putting brushes or pick-up wheels on the vehicle. That way the number of coils can be minimized.

What I am not sure of is whether the reaction plate can be continuous, or if it has to be segmented so as to take advantage of edge effects on the reaction rail. Hmmm...I wonder if I still have an HO-scale flat car around here.........

--Dave Althoff, Jr.

I tried the train track thing, but it wasnt successfull. I was prolly just doing it wrong. If you could, could you tell me almost exactly how to make it, or draw a picture and i could try again.