Re: Before I make a mistake, what do I need to know?

Balloonbuster,

Size is something that is easy to become pre-occupied with! :-)

Machines using size 23 motors are at work every day doing the type of
work you mentioned originally. Size 34 motors are available with
pretty high torques... So, IMO, you don't need to be thinking about
42's. And 42's WILL accelerate more slowly, compared to 34's, and
34's will accel/decel more slowly than 23's, etc. Since the machine
you plan will be making a series of short, small moves 42's again
will not be the best choice.

As Chris S mentioned, you have some of the venerable IBM printer
motors: 2°/step, 1.4A (so they could use "modified" 1/2 stepping,
where the current is increased when a single phase is active. This
means using 2A drives), and 4.5V. Size 34, single stack. Standard
shaft is 3/8 x 1-1/8. Made by fuji or astro-syn (japan servo). I have
used SCADS of these motors over the years...

They will work fine, and I have used them in leadscrew machines where
150ipm was achieved. Since this was 750 rpm, I can't agree with Chris
that they are only for "slow" usage. But then, slow and fast are
relative terms to begin with...

DEFINITELY use the center tap to end; regardless of bipolar or
unipolar! These are relatively high-inductance motors. The 297/298
drive will work well with these motors.

Nearly ALL the available control software will accomodate the 2°
versus 1.8° step size, so don't make it an issue. In the printers
these were originally made for, the half stepping made for 1°
rotations, and this fact makes these motors a good choice for rotary
applications.

Your last question depends on the definition of "homemade"! If you
look in the files section, you can see that Mariss shows his Gecko
drives as "homemade" :-)
Seriously, there are some EXCELLENT designs and drives made "at home"
which will easily compete with "manufactured" drives. And you can buy
drives of such quality and at such prices as to make it a hard
choice. The REAL answer is not home or mfr., but experience, design,
and execution; i.e., can you solder well? How about surface mount
parts?

Having said all this, the motors you are asking about will perform
well with a "homemade" drive. But the geckodrives are D#$% good.

Chris did a good job answering your 1 motor versus 2 question. I will
echo that it depends upon the design and size of the machine. Also
the type of linear bearings used. This second part is often
overlooked. A GOOD set of linear bearing MAY allow the use of a
single centered leadscrew, since they(the bearings) will not allow
the gantry(or table) to "skew". This level of bearing is expensive,
so it becomes, as nearly always it does with this cnc stuff, a choice
of WHERE to spend the bucks...

Hope this helps.

Ballendo

--- In CAD_CAM_EDM_DRO@y..., balloonbuster@h... wrote:
> Chris, thanks for the advice that you gave me. I still have some
> questions to ask.
> The stepper motors that I was going to use where Nema 34, 2
> degree/step unipolar ones. Since 1.8 degree/step is more common and
> since I don't want to have to change motors in the near future, I
was
> wondering what would be a better choice for motors. Should I go to
> the larger Nema 42 size. Would that give me more power plus speed
and
> what about the cost. And should I buy a true bipolar motor as
opposed
> to the unipolar ones.
> Is 2 motors necessary for the X axis for accuracy and no binding,
or
> is 1 motor enough
> Also, will a commercial controller, such as from Geckodrives, make
a
> lot of difference in preformance compared to a "home made" one.