RE: [CAD_CAM_EDM_DRO] Re: stepper driver help

OK, so 2mm pitch means you want speed above all else.
Never gear a stepper down. A 2:1 ratio means your stepper is spinning twice
as fast for the same table speed, and is generating half the torque, which
gets doubled by the ratio, so you're back where you started. If you need to
gear a stepper down to drive your table then your motor is too small for
the job.
As someone else pointed out, voltage gives you speed. Pick the drive that
can tolerate the highest voltage. At 2m/min, with 2mm screws, your motor is
spinning at 1000RPM, no stepper is drawing its rated current at that speed.

PK

-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of stefan_sharpe
Sent: Thursday, 27 September 2007 9:59 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: stepper driver help

> Most importantly, what screws are you using. They, more than

anything

> determine the required characteristics of the drive and motor.
> PK

The table (its a mini mill) has quite well made achme screws with a
2mm pitch- I have set these up to have very little 'backlash' (0.02-
0.03mm) and they are very free even just using the supplied backlash
adjustments, which, while they work, don`t seem to be ideal. With
some work I am thinking these can be improved on.

In the future I would like to think I`ll go to ball screws, but for
now, cost is a major factor- so el-cheapo achme it is.

I will make some toothed pullies for whatever toothed belts I can
find- this frees me up a little in terms of what reduction ratios I
can use, and previously 1:1.5 or 1:2 was mentioned. Again, I have
no experience of what the associated merits and problems are with
the stepper to lead screw conections are- I have read about
resonance being an issue but I just have not 'feel' for what is
going on here. Always nice to be right first time though- any advice
welcome!

> Gecko 201? About 100 $ see www.geckodrive.com
> 8 amps, very good.
>
> There are no restriction on using 2a bipolar chopper drives w.

nema23

> motors.
> The amps you can drive determine your torque.
> The volts determine your maximum speed & acceleration.

Thanks for that insight- these are just the kind of things I am
trying to figure out.

>
> What drives have you found ?
> There are very many drivers on the market, what is your main

concern/goal ?

> Cost ? Reliability ? Support ?
> A kit you solder ?
> It may help if you let us know what motors You have found.
> Of real interest, the most useful thing about them, is to know
> their speed/torque curve, nominal volts and inductance.

At the moment, cost is the big issue. I am also keen to solder up
my own drivers so I learn more about them as I go-

I have no motors yet.

Here are the two free circuits i found:

http://www.timeguy.com/cradek/cnc/stepper-drivers

and

here http://hans-w.com/modular_cnc.htm

>
> Ideally, you want motors that have maximum torque and speed in rpm.
> If possible, you should use motors that go to 1000-2000 rpm.
> A motor that will spin at 2000 rpm will be very much better.
> The difference may well be five-fold or more.

Thanks again for the great information. Those steppers you offered
for sale do sound good- I sent you an email regarding them- did you
get it?

Stefan




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