On Tue, 26 Nov 2013 09:06:18 -0800, etpm wrote:

On Tue, 26 Nov 2013 00:15:06 -0600, Tim Wescott
wrote:

On Mon, 25 Nov 2013 18:20:47 -0800, etpm wrote:

I've been looking at the brushless motors used for RC planes and the
like. They are amazingly powerful for their size. And they really spin
up fast! One web site has kits you can buy to wind your own armatures.
Anyway, I have been wanting a rotary tool that is a cross between a
Dremel and an air powered tool I have. Something with an OD of about 1
inch. Like a Foredom handpiece. Faster than any of my Dremels but
slower than my small air powered hanpiece that spins at 80,000 rpm. So
I'm thinking one of the "inrunner" type motors might work. At 80,000
rpm the surface speed is about 2600 SFPM. Even though the speed drops
quickly as soon as the rotary tool contacts the work the speed is
still too high for carbide on steel and the burrs and rotary files
dull quickly, which makes them cut slower. On the other hand, the
Dremel and Foredom rotary tools are too slow and this ends up costing
time too. Something that spins about 40,000 rpm and maintains that
speed along with the smaller diameter would be great. In fact, a tool
that was .75 or even .625 diameter would be even better. I have a
dental handpiece that I use for some delicate work and it is just
under .5 diameter and is very easy to hold because of the small
diameter. If I could build an electric rotary tool with the torque of
a Dremel, 40,000 rpm, and 1/2 inch in diameter I would be very happy.
Even one that matched the Dremel torque and speed specs but was 5/8 or
1/2 inch diameter would please me greatly. So, anyone here play with
brushless RC motors?
Thanks,
Eric,

Not for what you're contemplating -- but I do have a couple of RC planes
that I fly with them.

It may work. I'd use an ESC with a helicopter "governor" mode for
steady speed. Make sure you have lots of fan cooling -- those motors
get light in part by being designed for steady airflow (they're AIRPLANE
motors!! ). I wouldn't count on the motor bearings to hold up to much
side-force,
so you'll have to provide support against that.
I of course would only be subjecting the motor to torque forces. Robust
ball bearings are needed to support the cutting tool.

I never know what someone knows...

I didn't know
about the ESC "governor mode". Thanks for that.

Please submit a full report when you're done -- I think it's a cool idea.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com