I'm making another prototype. I'm not happy with the way the field windings turned out. The second winding tends to slip off. I revised the wire guides, and have lengthened the shield to better protect the windings.

I remember a design for a two phase micro brushless motor, using the magnet from a coreless pager motor (which might be simpler to come by and should have a suitable shaft already fitted). Essentially it had two cross shaped plates at either end with four "pillars" linking them at the corners. The windings went between these pretty much the same way as in your first prototype. I did try to find the pictures, but it's most likely buried deep in the archives of rcgroups. The design has long been superseded by the single phase hall controlled motor (essentially an actuator with no rotation limits), and is mostly used for sub-gram planes. There's also brushless conversions of coreless pager motors that use the original windings, but these are three phase motors, so not really suitable to work as an instrument.

edit: Oops, I just realized I made a mistake. Coreless motors have a static magnet, so the shaft won't really be fitted to the magnet. Sorry about that. OTOH, the magnet will be a nice cylinder polarized transversally, so it ought to be still good, but the shaft will have to be fitted to it somehow.

edit2: this thread in particular: http://www.rcgroups.com/forums/showthread.php?t=596219&pp=100&page=12 might be interesting for building and winding techniques.

Wow! That's some impressive miniture work.

Got the last prototype together.




Putting 5 volts on a field winding causes the rotor to respond nicely. The next step is to get the electronics working. I've more or less completed the hardware. I'm working on revising the firmware. I started with the firmware listing from an earlier air-core gauge project which uses a PIC16F628 operating at 12 MHz. The current hardware includes a PIC16F648A operating at 20 MHz. A few tweaks are in order. I also have to re-learn how to use the Microchip IDE... It's been awhile.

I have the electronics working well enough to spin the air-core shaft. Since the shaft is indeed turning smoothly, I consider the air-core movement functional and will shift my efforts to further testing of the electronics.