On Tue, 26 Nov 2013 12:56:10 -0800, etpm wrote:

On Tue, 26 Nov 2013 18:20:54 +0000 (UTC), Cydrome Leader
wrote:

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,

you may have problems unless them motor has internal position sensors/
more than three fat power leads. They're mean to run fans or a gearbox
and a fan with no sudden load changes. Brushless fan controllers don't
tend to like loads other than air, or they get confused and lock up and
do other nutty stuff.

The RC controllers may be more tolerant of this, but again, if the motor
lacks position sensors, it's probably not meant for dealing with abrupt
load changes or putting out lots of torque at low speeds.


I don't know how well the RC controllers will work either. My feeling is
that since they can spool up the motors pretty fast they will tolerate
some speed fluctuations from loads. I'm hoping the torque will be high
enough to keepthe speed fairly constant.
Eric

If not, the motors for RC cars have sensors. An RC car motor and ESC
combo should work down to zero speed, and not show the "nuttiness".

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com