Check the E-book at the top of the page For "Johnson counter" http://www.allaboutcircuits.com/vol_4/chpt_12/6.html Near the bottom of the page there are some 3PH circuits. The ones with a square wave could be used to switch some mosfets.

Don't think your going to be too successful with a linear induction. Takes to much current to generate the magnetism in the rotor/linear moving part. Have you seen these? http://www.h2wtech.com/Pages/DC-Linear-Brushless-Motors.aspx

Why are you so set against sharing what your doing? Top secret? There are a lot of other solutions to you problem if you would just share more of the requirements. There must be requirements to be met, right. Why not tell so we can help.

 

Its not that I'm trying to be specifically cryptic, I actually did not realize I was being so cryptic. My project involves a small 300-500 gram vehicle, levitated by an air cushion (similar to a hovercraft). The device is always withing a half cm of an aluminum wall, which is 5 mm thick. The idea here is to use the linear induction motor to utilize the wall as a means of propulsion, but its more like a reversed linear induction motor, because it is what is refered to as the stator moving, as in, the induced surface is actually stationary. This is not some strange or important project, this is just one of those things people do for fun, and my colleague and I (the one i mentioned is making the LIM, decided to do this as a project just for fun... No crucial importance, just as a pastime. I'm planning on having the "stator" and induced surface within a 1-2 mm distance from one another at any given point, and the power i have available can't exceed a 3s LiPo battery for the induction motor. I hope this makes more sense now... please refrain from asking me why I choose this strange project as a hobby... I hope I addressed all your questions. I hope you can all help. Thanks!

 

You do realize the the motor need a iron/magnetic, not aluminum, surface to work against, right. And that surface needs some kind of "salient" poles on it. To pull against as the magnets switch off and on in sequence.

Why not use some of the air thats trapped by the skirt of the hovercraft to push it forward? The propulsion air stream could be controlled by model airplane servos to make it go left and right and forward or reverse. Then it wouldn't need to be constrained against a wall. it could go any where then.

 

Not to be too nit-pick too much, but aluminum is a valid reaction source for linear motors. For single sided drive, a ferrous backing plate is used, but for dual sided, aluminum only. See the fifth paragraph here...... http://www.baldormotion.com/products/linearproducts/lmac.asp

 

You may have missed the part where that takes two motors with the aluminum plate between them.

" Using two LIMs facing each other can provide increased force. This is known as a double sided linear induction motor. Here the reaction plate will consist only of a 6.4mm (1/4 inch) thick aluminum plate without steel backing. The aluminum will require additional support over the length of the stroke " Fifth paragraph from the link.

Like in an induction motor the iron magnetizes to generate current in the "shorted rotor bars" (squirrel cage) of the rotor. In the use of the alum plate, it keeps the two stator/primaries apart.

Either way still don't think it can be done with 6 - 12 volts 4 amps.

 

http://emsa.gastli.net/Chapter8/Linear_Motors.pdf

See page 7.

As to previous post, dual sided is two (TOW) motors.

Agreed, the entire project seems to be beyond the limitations that have been set.

 

but there are 2 sides... the aluminum walls are on each side.. I doubt that helps, but I've seen a single sided LIM operate on aluminum, its not unheard of. A substance need not be magnetic for induction of eddy currents to occur, just conductive. Are you sure it is totally impossible? I've seen single sided aluminum based LIMS work with very little current of arround 5 amps with an similar sized air gap, again, not looking for any huge acceleration...

 

I'm wondering, if i simply used an existing ESC from a brushless motor, which should be able to drive a LIM, ignoring my previous requirement for 4 amps or lower, as I see some of these ESCs output over 25 amps peak current draw, would it then be possible to achieve some force from a LIM, even a small one? Single sided, aluminum inducted surfaces.

 

The only way to know for sure is to try it.