Homebuilt handmade "3 phase" electric motor

[skimask]

This is something I've been wanting to build since I was a kid...(and I really wish I had some pictures to post)...need some help figuring out where I went wrong. I got most of my info and research from Wikipedia, so we'll see how far that gets me...

I skipped right over the regular science fair project DC motor with a couple of nails for electromagnets and went for a '3 phase' (PIC controlled of course) synchronous motor...that's probably problem number one right there...

The rotor is an 10 inch piece of carbon-fiber/kevlar arrow shaft with a piece of 6 inch long, 3 inch diameter white PVC pipe with center drilled end caps mounted on it (the arrow shaft goes thru the middle of it and it's centered very well). I've got 2 pieces of 8 ga. solid copper wire around both end caps (a bit tough to bend) with 36 pieces of 8 ga. solid copper wire connecting both ends, equally spaced (or at least as close as I could get it), and each piece of wire connecting each end is soldered to the rings at both ends. And I've got all of that secured with a good coating of clear silicone and a few zip ties.

9 total field coil windings (3 each for each of the 3 phases), each one is a steel bar (6 inch long, 1/4" x 1/2" wide/thick), with 36 turns (12 turns, 3 layers deep) of 20 ga wire, equally spaced at 40 degree intervals around the rotor. The field coil windings are oriented so the thin edge of the bar (without the wires) is facing the rotor.

The main driver is a PIC running multiple H-bridge type setups using MOSFETs and driving the field coils with +/- 24v, current limited to about 3 amps per phase. Basically, each phase is being controlled like it's driving a reversible DC motor. Each phase steps in a sine wave like fashion, +24v, 0v, -24v, 0v, +24v, etc.

The controller part works just fine. I've got it set up so I can control and monitor RPM/frequency with my 'scope and I've got red/green LEDs on each phase and coil and I can watch them sequence correctly. Everything is isolated from everything else. The PIC controller runs off a NiMH pack, feeding optoisolators, which trigger the power MOSFETs, which run the coils from their own separate lead acid battery pack. I don't see any spikes at the PIC on the 'scope when the system is running.

But the motor doesn't spin!
I've got as tight of a gap as I can get between the rotor wires and the field coils, roughly less than 1/16".
The bearings that the arrow shaft rides on are nice and smooth and practically frictionless.
The rotor seems well balanced, I can't get it to stop at any single spot repeatedly during spin tests (both horizontally and vertically (even though I don't have any sort of thrust bearing on it).
As 'wikipedia' mentioned, I offset the ends of the rings on the rotor by about 10 degrees (supposed to help start it) making it look like the interconnecting wires are on at an angle.
I even tried turning the field coil windings/bars 90 degrees so that the wires were facing the rotor instead of the blank steel end, had to increase the air gap a bit, about 1/4", so that could've killed that idea.

The idea, according to wikipedia, is that the field coils induce current into the copper wiring on the rotor to set up a counterbalancing magnetic force which either attracts or repels the field coils on either side of it.

Any ideas where I went wrong?
( I mean besides the obvious skipping over the beginner's DC motor part... )

[skimask]

This is something I've been wanting to build since I was a kid...(and I really wish I had some pictures to post)...need some help figuring out where I went wrong.

Tried a couple of things today...
-Painted a black stripe on one end of the pipe, glued a piece of foil for a reflector, added a light source and a phototransistor, wrote some code, tried to get rotor to sync up with the software/MOSFETs. The motor didn't work, but the code works, I get a good rpm reading on the LCD.
-Replaced the resistors on the regulators, upped the current limit to about 5 amps. I'm afraid if I go much higher, I'll fry up some wiring.

Any other ideas?

[mackrackit]

You need something magnetic between the copper on the rotor. Think of the rotor as a shorted transformer. The copper rings and bars are the short.

Wiki should have said the idea is to induce a magnetic field, not current.

Think of putting a nail on a magnet and the nail will then be able once the magnet is removed, to pick up a paper clip. The nail will also have a N and S pole. Rotate the magnet and the nail will try to move (compass). The rotating field of the stator is doing the same thing to the laminates on the rotor. All the copper is doing is causing a short.

There are several theories for the shorting, The one I feel is correct is to create an insulation between the magnetic parts of the rotor.

Having the electro/mechanical part of the rotor on a twist does help starting as the magnetic parts will cross phase ( in two fields at the same time ) .

Over lapping the stator coils will also make a difference but what you have should move. (spin start? maybe) The bare metal in the stator coils should be facing the rotor, like you had in the first place.

Look at this http://ww1.microchip.com/downloads/e...tes/00887a.pdf

If this does not help, I have a friend who owns a re-wind shop. I will get his input.

[skimask]

You need something magnetic between the copper on the rotor. Think of the rotor as a shorted transformer. The copper rings and bars are the short.

So, you're saying, if I were to lay the rotor out flat, it would go: copper wire (shorted to every other piece of copper wire), insulator, slab of something magnetic-able, insulator, another copper wire, etc.etc. I'll give that a shot...

Wiki should have said the idea is to induce a magnetic field, not current.

It did...but it said inducing a current is basically a side effect of the magnetic field. Same thing but different...

Having the electro/mechanical part of the rotor on a twist does help starting as the magnetic parts will cross phase ( in two fields at the same time ) . Over lapping the stator coils will also make a difference but what you have should move. (spin start? maybe) The bare metal in the stator coils should be facing the rotor, like you had in the first place.

Overlap - I've tried a few different angles so far, even angling the stators the opposite way to the rotor angles...
Spin start - no joy...
Bare metal - that's what I thought...and I've put it back that way.

I just wanna see this thing spin so I can giggle like a little 12 year old...

[mackrackit]

So, you're saying, if I were to lay the rotor out flat, it would go: copper wire (shorted to every other piece of copper wire), insulator, slab of something magnetic-able, insulator, another copper wire, etc.etc. I'll give that a shot...

Yep, but you will not need the insulator. The current created and suppressed in the copper is the magnetic insulator.

It did...but it said inducing a current is basically a side effect of the magnetic field. Same thing but different...

OK, must have been a different article, looked it up on wiki to see where you were coming from. Chicken or egg, which came first?

Overlap - I've tried a few different angles so far, even angling the stators the opposite way to the rotor angles...
Spin start - no joy...
Bare metal - that's what I thought...and I've put it back that way.

Not sure about the spin start, never seen one with straight coils. You could add a start sequence to the code like a stepper if needed.
Attached is a bad drawing of what I mean.

I just wanna see this thing spin so I can giggle like a little 12 year old...

Always nice to do something for fun, and not have a dead line.

[mackrackit]

Might be able to use welding rod between the copper on the rotor. Flux not included

[skimask]

Yep, but you will not need the insulator. The current created and suppressed in the copper is the magnetic insulator.

I meant that in terms of electrical insulator, like a thin piece of plastic or something.

Attached is a bad drawing of what I mean.

Yep, that's what it looks like, roughly...same idea all around.

I wonder, if and when I get this thing going, how much power I'll be able to pull out of it.
Rebuild it, put a bigger shaft in it, beefier wiring, bigger copper, and so on and son on...
I wonder what the limit would be...on a beer budget anyways...