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Large Radius High Speed Stepper Motor

Hi,

I am trying to make a fan using a stepper motor where the radius of the rotor is very large, say, 1 meter, and the drive is applied at the periphery of the fan (the fan will have a rim at the outer circumference).

I want super high rotational speed. The faster the better. Natuarlly the atmospheric drag will increase with the rotational velocity, but I was hoping that I could simply increase the speed by increasing the power delivered.

I can drive the stators in any sequence at any rate with any amount of current under software control (USB).

Is there a speed beyond which there is a fundamental limitation on how fast I can pulse my stators? Can I expect to be able to get the fan to turn faster simply by increasing power? What type of efficiency can I expect (electrical power to frictional atmospheric forces?) I am assuming that efficency losses will be in joule heating and radiation, so it seems that I should be able to get high efficiency. And finally, a big one, what is the optimum geometry of the magnetic assembly at the perimeter? How many magnets should I use? Is more really better? Should I use some sort of super cap array to deliver the pulses? What types of (electro) magnets should I use? Will I have to worry about vibration? Lubrication? Metal bearings for direct contact? d-phi-b-dt effects?

I know I am asking a lot, and I don't need all the answers now, just some hints to keep me from trying all the silly things.

-Chaud Lapin-

Reply to
unoriginal_username
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You increase the speed of a stepper by increasing the step frequency. It will have a huge angular momentum, so don't try to accelerate quickly. But why a stepper motor? Surely you don't need to control the instantaneous position of a fan? I would have thought a linear induction motor operating on an aluminium band round the rim would have been a lot easier.

Paul Burke

Reply to
Paul Burke

Hi! You are indeed looking for trouble!

Of course it takes power to do work (move air)... So you're right on that one. Fast rotation of a 2m diameter rotor: kWs - and a lot of them....

You'll burn a lot in driver/coil losses.

What's the application? Sounds like a no go in my ears... I'd go for more smaller (traditional) fans.

Cheers, Anders

Reply to
Anders F

It

quickly.

induction

lot

Hi Paul,

No, I don't need to be able to control the position accurately, but I would like to be able to reverse the direction. It's ok that the blades would have high angular momentum. As a matter of fact, I was thinking that it might actually be better that there is some rotational kinetic engergy for stability.

My overall concern, I guess, is to get maximum efficieny in transfer of engery from an electrical source to the blades, either in the rotational kinetic enery or through forced movement of air by the blades. I am going to check out the linear induction motor.

-Chaud Lapin-

Reply to
unoriginal_username

more

Hallo Anders,

The application (among other things) is a wind tunnel where the input is free-atmosphere. Again, the radius of the fan needs to be 1 meter at least.

I am mostly concerned with the efficiency of transfer of energy from an electrical source. Though I have near-zero experience with stepper motors (college work is over a decade old), it seemed intuitive that placing the magnetic drive at the perimeter of a large radius and pulsing the stators under software control at just the right moments could yield some very interesting scenarios. I also get the feeling that brief pulses delivered through low-reistance coils will minimize core losses. I would use standard techniques like quadrature to determine angular position and velocity. The key in all of this would be the software, not so much to force the rotor to assume a certain rotational pattern, but to make the rotor turns as fast as possible using strategically activated pulses, more or lest opportunistically.

-Chaud Lapin-

Reply to
unoriginal_username

Do some math on the angular momentum. Since you want the rotating part of the motor to be on the circumference, the largest concentration of mass will also be there which is the worst possible place. The requirement for the tensile strength of the blades will doom the project.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs

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Reply to
Boris Mohar

will

Having some experience with a BIG fan wind tunnel Boris is right. I've worked on a large fan ( 6Mw motor, folker craft wing segments for the blades) You dont want the mass on the outside of something that big.

Pat

Reply to
Pat Ford

Remember that power goes as roughly the cube of speed. Doubling the speed takes about 8 times the power.

The stator is inductive. The rotor shunts that inductance with some resistance. All energy you put into the inductance must be removed when you stop the current. You will be sloshing around large amounts of energy. The faster you go, the higher the losses.

No, supercaps have too much internal resistance. You are better off trying to ensure that the current draw is near constant for the whole assembly.

Very expensive LN2 cooled or LHe cooled ones.

I wouldn't call it worry. Something closer to !!!!PANIC!!!! would be the right level.

If you are going fast, air bearings are the way to go.

--
--
kensmith@rahul.net   forging knowledge
Reply to
Ken Smith

It

quickly.

induction

lot

Well, I must say, I feel like a dummy. LIM is exactly what I had in mind.

Not like I thought the idea was new or anything, but all the various "extra" features that I thought I could add like rapidily discharching stored engergy using supercaps has already been done. That are several nice, big, fat juicy papers put out by U.S. Department of Energy on this subject.

-Chaud Lapin-

Reply to
unoriginal_username

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