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Old 08-25-2015, 04:21 PM
MadMack MadMack is offline
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Join Date: Apr 2015
Posts: 73
Everyone, thank you for your interest. I'm glad to see I have the attention of some of the real builders here. If anyone can get this, it's you guys.

Charly2, yes that is what I described. Think bigger diameter & more side spacing between magnets.

Ewizard, round magnets might not make a difference but I can't say. I always used square or rectangular magnets, much easier to work with.

Everyone, I have to be very careful here because I'm bound by an NDA. I can not post the design drawings or any images and I can't reveal privileged construction details. However, anything else is fair game. I'm sure you guys can read between the lines and see my situation, and understand what I am trying to prevent.

BTW, when I write about things like this I tend to sound like I'm instructing a class of high school sophomores. Sorry, I can't seem to write any other way, so please overlook my condescending tone.

That being said.... If you are serious about looking into this be forewarned, you must be meticulous in the construction or you will fail. This has nothing to do with magnetic shielding but there may be some flux redirection involved. Later, maybe.

As Dave pointed out, it's hard to find two magnets with the exact same strength. Generally, the field varies inversely by the square of distance, at close spacing anyway, so a simple mechanical test rig can be made to determine which magnets are closest in strength. Alternately it can be used to find the weakest magnet, then to determine the distance at which the other magnets exhibit the same strength. Then you can know the clearance to use with the individual magnets. Do this with both the rotor and stator magnets before construction begins.

The closer the gap between the rotor and stator magnets the more critical the individual magnet clearances become. There is a huge difference in pull between 0.030 and 0.090 gaps. Don't forget to consider any clearance in the rotor shaft and bearings. Shoot for a tight slip fit between the bearing and shaft. Roller bearings would be a good idea I think.

If you decide to pursue this, may I suggest a two pole rig to start with? A 1 thick x 12 long flat with rectangular cross section and a shaft at dead center might make a good rotor to experiment with. One cube magnet each end on the center line, same polarity out. Now might be a good time to review the part in my first post about the rotor magnets and torque. Balance the rotor like you would a lawn mower blade. Then you could mount this parallel to another flat stock, say about 20 square, with two long stator magnets attached to it, 180 degrees and 12+ apart, N-S facing each other. With a rig like that you could try different clearances and magnet positions, etc. The first goal to achieve would be a symmetrical cancellation of magnetic drag. Balance the push and pull and get the rotor to spin past the stator magnets without magnetic drag, and without using any iron ramps.

On a side note, K&J Magnetics carries N52 neos, 1/2 cubes as well as 1/2 x 1/2 x 1 long ones, magnetized through their length. They even have the cubes with a mounting hole through their center that will accept a long machine screw if you dress the threads a little bit. Also you might be interested in looking at McMaster-Carr part number 5913K61 bearings and 1346K17 shaft.

Regards,
Mack
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