Hi, and again, thanks for the positiv spirit.
“What did you have in mind to run this motor in, perhaps an ultralight plane?â€Â
I have though about building a paramotor back pack. I used to have a paragliding license, but I have decided to put it in a Yamaha 125TZR motorcycle to get more every day use out off it. It seems to work well, it drives the motorcycles wheel with its original gearing 16-45 = 1:2.8.
Still some work to do before I try to register the bike properly.
“My interest in electric props are not for flight but instead for an electric "air boat"... sorta like a Florida airboat-lite, without the same noise and stink!â€Â
That would be a great project!
“Was the reason for dumping the little HC controllers because of sync issues?â€Â
No, there was never a problem about sync!
It was the non-existing chance that I would get the motorcycle approved for legal road use with that set up, since the motorcycle would not be able to start reliable from zero speed and absolutely not if you would start going up hill. So: no it will not start from zero rpm with strong torque. But once spinning there is a lot of power.
“Any estimates of efficiency?â€Â
Sorry, I do not have any reliably numbers. I really would love to find out.
I imagine peak efficiency is above 90%
“Any coil cross-talk related issues that you observed? Like bizarre ESC function and jitters?â€Â
No cross talk, sometimes a litter jitter going from zero to a couple of rpm
“Does using a conductive material to hold the coils in place cause inductive heating in the material and drop efficiency?â€Â
Drop in efficiency? He, he, you better believe it!
A rotor fitted with magnets this size will heat up a 2mm thick aluminium metal sheet to over 100 degrees C (water boiling point) in few,(like 3-5) seconds if the sheet is forced to stay within 5mm distance from the spinning magnets. You need to mount the sheet very firmly to prevent it from twisting if you would like to carry out this experiment. So sorry, no simple coil-heat transfer solution there. That’s eddy currents for you!
How ever, it seems to be possible to make a carbon fibre version without the eddy current problem since the carbon is a poor conductor.
“Any coil cooling issues?â€Â
Well, that is of course just a matter of how much current you wish to run through the coils…
But a hint is: in the 7kW clip the coil temperature seems to settle at just under 50 degrees C with an ambient temperature of about 25 degrees C.
I have built several water-cooled axial flux versions as well, not this big though.So if heating will become an issue later on I will try and build this motor in water cooled version as well.
“With zero cogging loss, would making as flat of spirals as possible, and mounting the magnets with as close to zero clearance as possible be optimal?â€Â
I do not know.
I have built one stator in this diameter 4mm thick. This was the carbon fibre coated one. The carbon fibre was necessary to make the structure stiff enough.
I did not carry out extensive data collecting with this setup. I think that the problem is that the air gap that the not professionally built motor inevitably will have, starts to be quite a large percentage of the total gap between the rotors in which you also like to have the copper wire if you build extremely thin stators.
I have found 7-10mm stator thickness to suit my limited ability to produce high precision parts.
“Did your coils deform from magnetic stresses?â€Â
No, not yet.
“I would like to build a motor much like this motor. Do you have any special concerns or advise you would give?â€Â
Good question, Im still in the learning processes my self.
Be careful when running a high rpm and be sure to reinforce the magnets properly with carbon fibre. Don’t forget to mount a temperature sensor next to a coil since heat is the limiting factor.
“Things you would do differently if you could do it again?â€Â
Good question, Im still in the learning process my self.
I will have to get back to you on that one.
“What did you use for bearings in the prototype?â€Â
Ordinary cheap ball bearings with rubber sealing. Really nothing fancy.
“What thought process did you use to decide on the coreless coils? Assuming cores were a consideration.â€Â
Simply DIY-billety. It is to hard to find appropriate stator lamination material not to mention processing it.
It is possible to build this motor without a lathe. You basically only need a drill press, a bench belt sander and a hand held milling machine for wood, what is it called?
“The Jig set up at .09 in the video. Is that for building the strand count for the coils all
the same length? or the apparent carbon fibre magnet retention lamination?â€Â
It’s a simple way of measuring length and number of strands of copper wire. And picking up a little sun tan as well!
In a first build it might be easier to use a single copper wire although the coils might be a little more bouncy and give higher eddy current loses.
“Any idea of the Kv?â€Â
Yes I have. I have built several different versions. The one mounted in the Yamaha has a kv of 68rpm/v with a given set of magnets (30x10mm N45 magnetisation grade). The same magnets mounted on a rotor with a layer of iron on the backside of the magnet gives the motor a kv of 58rp/v at the cost of a 1.5kg heavier motor. On of the brilliant things building a motor yourself is that you only have to make a new stator. The rotor fits both thick and thin versions.
/Axel