Yes, I know pwm is trivial these days and I've done it a few times in other
projects, but we had just finished making a board with a pic and spi 12 bit
dac to generate a 0-5v signal to drive the motor that we planned to use
because that's what that controller wanted, and I had hoped that the rc
motor and esc would drop into that without any extra fiddling. If the rc
motor had worked out as a lower cost alternative we would have redone the
board, but it didn't.

Thanks, Roger, for the explanation of why the odd timings. I knew I was
close but not quite right on the timings, but the point was to make sure
Eric knew what an rc esc needs to be fed for control so he wouldn't get the
same surprise I did after buying the motors, instead of before :-).

-----
Regards,
Carl Ijames
"Richard" wrote in message
m...

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/