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----- Original Message -----
From: <stratton@...>
To: <CAD_CAM_EDM_DRO@...>
Sent: Wednesday, February 23, 2000 11:51 PM
Subject: Re: [CAD_CAM_EDM_DRO]

From: stratton@...

Joel wrote:

I'm working on a chopper drive for the motors. I have a prototype up and
running. So far I've got the current up to 3 amps/phase. With two

phases

energized it's drawing less than 500ma from my 40 volt supply. It's
designed to go up to 5 amps but I'm stopped here till I get some

instability

issues worked out. It seems to have some problems at certain motor

speeds -

I believe it's caused by the physical resonance of the motor armature.

I'm sure I'm not the only one who'd be interested in hearing what you
chose for a drive circuit, if you'd be willing to briefly describe it.

Chris

Sure Chris, I'm using discrete mosfets for drive, and a microcontroller
for brains. The micro is very flexible in that I can do half step, half
power, power saver, and reverse direction signal by reading jumpers during
initialization. The micro has two analog comparitors built-in that are used
for current sensing. The micro can program the reference voltage for the
current sense so it can do half power and power saver. Power saver is going
to 1/2 current if the controller has not received a step pulse in a second
or two - it will immediately go back to full power to make the step when it
gets another pulse. I can also program the step pulse edge + or -. The
prototype has it's own 5v logic supply derived from the 40v input. I don't
know if this list accepts attachments so here is a link to a picture of it
if you want to take a look.

www.spyparts.com/users/jj/driver.jpg

I also have some pictures of my mill there that I'm trying to CNC. they are.

www.spyparts.com/users/jj/mill1.jpg
www.spyparts.com/users/jj/mill2.jpg
www.spyparts.com/users/jj/mill3.jpg


Joel