# Linear Motor



## piotrsko (Dec 9, 2007)

space rail gun count?


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## Hollie Maea (Dec 9, 2009)

Sounds good to me!


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## PStechPaul (May 1, 2012)

There is a difference between railguns and linear induction motors:





 




 




 
Railgun:


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## Hollie Maea (Dec 9, 2009)

Yes, I know...my response was tongue in cheek. I am not super interested in rail guns at the very moment...


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## PStechPaul (May 1, 2012)

It looks like there are two basic ways to build a linear induction motor. One way is to have multiple electromagnets on the track, fed with three phase, and use a conductive metal piece into which eddy currents will be induced to cause the thrust as seen in the roller coaster as well as the less impressive motor made by Daniel. The other concept uses a three phase current source and electromagnets in the moving part, and the rails can be just conductive metal.

I'm sure it can be enhanced by using laminated iron and a linear squirrel cage construction (like a ladder) for the linear "rotor". There are also some permanent magnet synchronous designs. It should also be possible to use the principles of a switched reluctance machine.

The railgun principle uses the Lorentz force and will operate with DC or AC current without ferromagnetic components. It is the same principle as I showed in one of my videos where a current of 200 amps in a loop of wire braid causes it to "jump" and spread apart. I think the force is proportional to ampere-turns, and requires a lot of current because you really have just one turn. But I wonder if it's possible to make something with more turns (multiple rails) so lower current and higher voltage could be used?

Sounds like it could be an interesting project.


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## Hollie Maea (Dec 9, 2009)

We're just getting started on this project. Digging through the theory now...we'll start small before we scale up into the tens of megawatts.


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## kennybobby (Aug 10, 2012)

*Re: Linear Motors are fun!*

i have a some experience with several different types: induction, synchronous and PM. The induction type worked the best and could be four-quadrant controlled and it made over 15 tons of thrust in a locked-rotor test while drawing 4.5 kamps. 

One concept that is somewhat easy to consider is that of a 3-phase AC induction motor, then slit the lamination stack and unroll it out flat. Take a second motor and repeat, then stand them up with the slots facing each other and align the pole teeth, with a gap for the 'rotor', a rectangular aluminum plate about the size of the lamination stack. The windings can be wired in series, parallel, wye or delta and then use an industrial variable frequency inverter to run it. Of course you can't really unroll a lam stack and will have to build your own back iron, but here's a hint to simplify making the laminations--if you have a way to secure the windings to the back iron then the motor will work just fine or even better without the need for pole teeth in the stack and you can eliminate losses due to the end turns. Have fun!


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