On Mon, 02 Dec 2013 19:27:33 +0000, David Billington
wrote:

On 02/12/13 05:00, Richard wrote:
On 12/1/2013 10:42 PM, Carl Ijames wrote:

I wanted to try one of these as a cheap alternative to a conventional
brushless dc motor in a mechanism we were prototyping at work, so I
grabbed
a couple with controllers off ebay to explore. Then I learned that the
control input needed to be a variable duty cycle digital signal,
something
like (from old memory so I'm sure it's a little off) 10 or 15 ms
period and
0-5 msec on time for 0-100% of motor speed, sigh. I used a signal
generator
to fake it for the initial tests but it would have been a pain to
drive it
with our controller if it had worked out (we were set up to output
0-5V for
0-100% motor speed). After getting the parts it was clear that the
ESC and
the motor winding could handle some pretty hefty currents to make the hp
they claimed, but there was no way they could dissipate even 10% of the
resultant heat steady state. These were airplane motors and ESC's so
they
were engineered to run for 1-2 minutes max, and then have many, many
minutes
of cool down time while the battery pack was recharged or swapped
out. The
motor bearings were pretty wimpy, too, so I was afraid that putting a
pulley
on the motor shaft and having the lateral load from a belt would kill
things
pretty quickly, but I never got that far since it was obvious that the
package wasn't what we needed. Hey, it was a fun experiment, anyway
:-).
I'll dig one out Monday or Tuesday and see what rpm it's rated for,
maybe
you could play with one.

-----
Regards,
Carl Ijames



I don't know anything about your controller, Carl, but pulse width
modulation is really fairly trivial (these days!).

http://www.instructables.com/id/QuickStart-one-transistor-DC-motor-controller/


Probably a bit over the top for controlling a hand piece. I bought a
servo tester from Conrad while I was in Munich about 20 years ago and
they still do them, see http://www.conrad.com/ce/en/product/234915/ .
That'll give manual control on the PWM that can then be supplied to the
ESC. I don't know if Conrad have a US branch but some digging might
reveal the circuit diagram which from memory was quite simple and used a
common 4000 series CMOS chip. Looking in the downloadable documents
section and the first file shows the circuit diagram and it uses a 4001
and a few discrete components, simples!.
It looks like Hobby King has a motor or two that will work. Along with
an ESC and a servo tester. I also found a circuit for building my own
servo tester. I could hook up my Basic Stamp too. But for 5 bucks I'll
get the one that comes in a box. Thanks everyone so far for the
replies. I know the inrunner motors will overheat if run at high
currents for too long. I will need to come up with some type of
cooling scheme. I am amazed by the power of these little motors. A
20mm diameter motor thats rated at 330 watts! Of course the motor
would melt if not kept cool. Maybe I should connect a coolant hose and
run LN2 from a thermos through the thing.
Eric