Michael A. Terrell wrote:
Jamie wrote:
Michael A. Terrell wrote:
Claude Desjardins wrote:
wrote:
Unfortuantely it doesn't seem that simple. The speed control has what
looks like a some kind of semiconductor/IC (3 leads), a diode, and
maybe a fixed resistor in addition to the slide pot. I don't know if
they're doing pulse width modulation or what.
I doubt they have put a stepper motor in there, they wouldn't sell for
20$ each! -- You still should only have two leads coming out of the
motor. Confirm?
Every Dremel tool I've had apart used a universal motor, and the
speed control was a simple dimmer circuit. This one might be PWM, and
run the motor on DC.
Most of the cordless drills these days use PWM power FeT drivers.
I modified a cordless drill with a mini PIC and Bridge to
perform regulated torque control, auto reverse and then forward
again until maximum torque was no longer peaking. Did this so that
the drill would have a TAP mode in it. I stuck a mini pot on the back
side of the handle to set the torque level.
if his dremel is also cordless, It may also be using it a PWM?
who knows. how ever, with the part count, I'm guessing he's using a
corded unit with a phase control.
None of those I've seen used an IC in the speed control. Also, he
didn't mention a filter capacitor, so id may be a simple dimmer
circuit. It's hard to tell from such a vague description. Part numbers
would have been a big help.
BTW, have you seen the small DC powered clone at Harbor Freight? It
runs on 12 VDC, and comes with an AC adapter. I was thinking about
using one (or more, with different sized drills) with a homebrew CNC
machine to drill PC boards.
Hmm, No, I haven't checked into Harbor Freight in some time how ever, I
think you'll find that a lot of named brand tools we know are now being
made by the same people that make the no-name brands from China.
For example, I have a rotary tool that in all respects is a dremal.
bu t the name isn't of course.
As far as drills with PWM, the Craftsman 1/2 drive chuck cordless uses
PWM driver board which is mounted as part of the trigger. the speed pot
slider is on the board. It employs an IC chip with a logic level Power Fet.
We have some electric real movers that are still being modified by the
manufacturer because they can't seem to get one to last any longer than
2 months in our shop. First they had drive problems where it wouldn't
start half the time. This was an elaborate board with a micro driving
what looked like a Mosfet H-bridge.
Any ways, we sent them back, the next set that came our way, they
modified with the speed control in the handle of the unit. All they
did was employ a speed control trigger slide switch from some existing
cordless drill system.
Those were very simply units, a single Power Fet with a 555 timer
driving it. Not sure if it was variable freq pulsed or PWM? Anyways,
those have a switch in the slide that initially connected the + batt
lead to the Vcc and Drain of the Powerfet. the Minimum speed was too
much on initial start. Those would burned them self's up in the switch.!
oh well, so much for engineering.
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5