On Sunday 28 September 2008, Ian Wright wrote:
>>>>>>>>>Ian, I think it's great that you would build your own driver.
>
>But to do so is not for the sake of saving money.
>Maybe as a learning excersize, but not to save money.>>>>>>>>>>>
>
>Thanks for the replies guys - from all the traffic I seem to have generated,
> I guess I may have bitten off more than I can chew at present. I do have a
> couple of real simple driver boards which will drive the motors but they,
> and particularly the motors, get hot as hell when the motors are not moving
> and I was a bit afraid that they may fry themselves. I had hoped that there
> may be a relatively easy way to do a chopper drive with current control - I
> had naively thought that maybe it would be possible to grab a current
> reference from a higher powered FET output stage ( maybe driven by the
> existing output FETs/ Transistors) and feed that back into one of the
> 'standard' microstepping designs - perhaps even using another PIC chip as
> the current controller. As I said before, I guess I'm somewhat out of my
> depth here and since, while the 'spares box' is full of electronics bits,
> the bank is somewhat depleted, it looks like I may just have to root out a
> few big fans and go with what I've got....
Years ago, before chopper drives came about, there used to be huge banks of
high power resistors used in series with each winding, used to control the
currents when high voltages were used to get some decent speeds out of
steppers. So heat some big resistors instead of the motors. Hot is ok, hot
as hell isn't. Set the supply to get a bit less than the motors ratings
through each winding, and/or set the resistor size and wattage to suit the
available supply. I've seen those big 200+ watt ceramic tube resistors used,
one per winding. A dozen for a 3 axis setup. OTOH, they will probably
deplete the bank account worse than the modern drives would. There isn't
much of a market, and those I need to keep our old GE transmitter running are
apparently being made to order these days, over $150 each, cash with order,
and around 8 weeks ARO.
Oh, and pipe the hot air out of the top of the resistor cabinet out of the
shop unless its wintertime & you need the heat. :)
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Martin was probably ripping them off. That's some family, isn't it?
Incest, prostitution, fanaticism, software.
-- Charles Willeford, "Miami Blues"
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