Flat coils and flat stator

[Dave B]

How do you keep the coils flat when exiting the interior coil wire over the windings ? I know this only amounts to the thickness of the wire but it seems to me that unless you make the total thickness of the coils less than the thickness of your mold that when casting and squeezing the top tight you could possibly warp the mold ? Maybe this had something to do with the previous post on a warped stator ? Any tips on this before I move toward casting my stator ? Thank you,  Dave B.

[Flux]

If you screw the lid on the mould or use clamps you will likely get a warped stator.

If you put the bottom of the mould on a flat surface and you keep the lid on with weights then it will not warp.

You are quit right that the wire wastes space and complicates the moulding process.

This has come up before and there has been a fair bit of discussion on the merits of bringing out the centre as a spiral winding and winding the coil in two halves in opposite directions with the inner ends linked.

I use bits of copper tape about 1/4" wide and .010" thick and that seems to work ok.

Alternatively if you don't cast the magnets into the rotors you can bring the centre connections out at the outside and use a stepped mould with clearance beyond the magnets. This doesn't work if you cast the magnets into a block.

[Titantornado]

I simply made my stator mold a little thicker (deeper) outside the area covered by the rotors.

Details here: http://www.fieldlines.com/story/2006/5/28/134138/175

[Ungrounded Lightning Rod]

You wind them in a form with flat sides and exit the middle wire at what will be the outside portion of the coil.

The sides of the form keep the coil flat, while exiting the wire at a turnaround rather than a between-poles secion causes the winding to become marginally wider radially at the turnaround - where it won't interfere with a coil beside it.

Winding with copper strip is more problematic:  You could fold the stip on 45 degree bends to bring it up and then out parallel to the surface - and you would do that in the outer turnaround so the magnets won't cause big eddy currents in it.  But it's still going to make the form thicker by the thickness of the strip plus the clearance under it, in the region of interest.  (This sort of thing is done for the field windings of automotive starter motors, which are generally wound with copper strip.)

If I was going to cast a stator with strip-coils completely imbedded I'd use an donut-shaped intsert in the final casting form to make the region where the magnets pass (plus a bit more for airflow) thinner on the side where the strips make their exit, so the magnets can sink below the surface on that side if necessary to get the gap right.  But I'd prefer to leave the outer loops un-imbedded (except for a thin protective paint job) to serve as cooling fins for the coils - in which case I'd fold the inner run to end up edge-on to the wind to avoid blocking the cooling air.