On Tuesday, November 26, 2013 1:20:54 PM UTC-5, 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.

Outrunners are pretty tolerant of what you describe (lotsa spinning mass), inrunners might be more sensitive, but as long as it's spinning fairly quickly it should work. With no prop I've put loads on my motors with my hand- at small throttle settings, heh.

This application would work best with 'low timing', that is, not a lot of advance. There are also settings for PWM frequency.

Neither outrunner nor inrunner will like starting with a large load (which shouldn't be an issue with this app).