Lee,

Another slightly delayed response, but I might be able to offer some 
assistance...

First, 8A is *significant*.  What motor is this for?  If you are looking for 
~700 oz-in motors, you won't need 8A.  Check out 
http://www.seanet.com/~dmauch/ .  He has steppers in this range, which many 
people on the lathe/mill/CNC lists are happy with.  As an example, he has a 
680 oz-in motor, requiring 2A, for $95 each.

For the drivers, check out Microchip's AN906 and also the datasheet for 
National's LM18245 stepper driver chip.  These explain a lot of how to design 
a stepper driver and about microstepping, etc.

(Currently, I'm building a couple 3A bipolar stepper drivers using the LM18245 
chip for my CNC lathe conversion.)

You should also get on some of the CNC discussion lists on yahoo groups such 
as DIY_CNC, CAD_CAM_EDM_DRO, and others.

Cheers,
-Neil.



On Friday 15 October 2004 09:03 pm, Lee McLaren scribbled:
> Hi All,
>
> I am looking for a way to drive a high power stepper motor, my current
> understanding (open to correction!) is that to achieve a high step rate
> with good torque you need to drive say a 8A 3V stepper with 80v which of
> course current limits to the appropiate value once the emf builds up. From
> my research some of the commercial units use even higher voltages up to
> 180v to maintain torque at high step rates.
>
> There seems to be a lot of info on the web but very little when current and
> voltage requirement get up a bit.
>
> I have looked at the linistepper and quite a few others and have found a
> PIC based stepper driver that that does the logic conversion  but I need to
> find a suitable output stage, I am guessing that I will probably need some
> sort of switch mode current limiter as a linear current limiter would have
> a very hign dissipation (800w!). FETs seem to be common in this area but
> again I am open to suggestions.
>
> I am also looking for a source of large stepper motors in the area of 5NM
> or 700 Oz/inches holding torque.
>
> Any suggestions?
>
>
> regards
>
> Lee McLaren
>
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