Re: Simple stepper motor question

> From: drew@...
>
> Hi All,
>
> Given all the discussion lately about Servo systems and such,
> I hope this isn't too simple a question but I've been wanting to
> build some kind of a small simple XY platform lately and have been
> looking into stepper motors. I guess I've been using the term alot
> around the family because my daughter gave me one for my birthday.
> As luck would have it, I she picked a Minebea Astrosyn 23LQ-
> C202-01H from Jameco which is a bipolar 1.9V .75A motor. I have
> a wiring diagram and an example schematic of a driving circut
> using discreet transistors but I've been trying to find a H-bridge
> like chip which I could use instead. I want to drive the motor by
> controling the phases in software so I don't want a translator
> chip. So far about the only chip I've found which I "think" will
> work is an L293B but I'm concerned about the low motor voltage.
> From looking at the data sheets it seems that chips like the
> TI 754410 and the L298 won't work with a motor voltage of only
> 1.9 volts. Is this the case with the L293B also?
>

Even though the motor is only rated at 1.9 volts, you want to drive it
with a higher voltage to overcome its inductive reactance. This is
done using a small resistor in series with the motor to sense the
current and a circuit called a chopper which turns the juice on and
off so that the average current is within the allowable range of the
motor. This lets you issue steps much faster than if you had to wait
for the low 1.9v rated drive to ramp up to full current through the
winding inductance. The 293 may be set up to facilitate this by
putting the resistor between the bottom end of its bridge and ground.

If you get the companion translator chip, that will handle the
chopping for your. You will likely find that the motor your daughter
so thoughtfully provided is good for learning how to build a working
circuit, however it will probably be too small to run a machine tool.

Chris

--
Christopher C. Stratton, stratton@...
Engineer, Instrument Maker & Horn Player
(978)538-5179 work, (617)492-3358 home
30 Griswold Street Cambridge, MA 02138
http://www.mdc.net/~stratton