Finishing Up the Coreless Motor

First, some photos taken with one of Bayley's magical cameras:

Sorry I didn't focus it well enough to achieve the full 25 megapixels of resolution, Bayley

After last round, the only thing left to make was a ring to separate the two halves of the rotor.   I CNC milled these two rings out of solid 10mm plate, using a 1/8" carbide endmill.  (Very) Subtractive manufacturing for the win.

As you can see here, I really didn't leave much clearance room around the stator.  If I had made the motor any bigger, however, it would have been too large to machine on the MITERS CNC mill, which is limited to 7" of Y-axis travel.

A problem with the stacked-parallel-plates construction is that it is really hard to actually get the stacked plates completely parallel.  I spent way too long trying to get rid of the little bit of skew between the two halves of the rotor.  I was able to make it acceptable, but not nearly as perfect as I would have liked.

As predicted, with both halves of the rotor installed, the circulating-current drag I noticed before disappears.  Here's the motor spinning up at 24 V on a generic hobbyking airplane controller:

At full speed on 24 volts, the motor draws 2.4 amps.  Not too bad, really.  The spin-down time is satisfyingly long as well.  

Drill-scoping across the leads put the motor at 97 rpm/volt, which is a bit higher than I expected.  Maybe the lost torque constant comes from my modeling of the motor about its average radius, or the magnets being a bit weaker than FEMM thought.  Still, not too bad for a first try.  If I could figure out how to easily wind it with wire, moving to a more Servodisc-style winding pattern could give a pretty decent bump in torque constant while still allowing the stator to be constant thickness.

Line-to line resistance is 100 mΩ, or 50 mΩ per phase.  So in terms of motor constant (Kt/√resistance), this thing comes a bit ahead of the venerable 80-100 "Melon" airplane motor.  I just measured one of the 170 rpm/volt flavor at 50 mΩ line-to line.  Realistically, in its current form it's probably very thermally limited, but this is still a pretty sweet result.  Now I just need to find some derpy vehicle to attach it to.