Re: houston plotter stepmotors
Posted by
ballendo@y...
on 2000-09-06 03:19:00 UTC
Bill Darby wrote:
likely. Older plotter,53 oz. in.,etc. What size are they?
<Newbie info alert>
Step motor frame sizes are usually a number which relates to the
approximate distance across the MOUNTING face. Some standard sizes
are 11(about 1.1 inches across) 17 (about 1.7 inch) 23( about 2.3
inch) 34 (3.4 inch) 42 (4.2 inch). Mostly we use the 23,34,and 42
sizes. The 23 is sometimes called a 60 (size of face in mm's) and the
34 is sometimes called a 90 (size across mount in mm's).
A second term you will hear (referring to steppers) is "stack".
Usually single, double or triple stack motors are used. The rotor
inside the motor(s)is made longer in more powerful motors of a given
frame size. And a second or third "stack" of iron is used. A 23
single stack (which I believe Bill may have in his plotter) is about
the size of a 2 1/4 inch cube. Very commonly, an older motor this
size is about 50 oz. in. torque. (new motors use better magnets for
more torque in the same size) A 23 DOUBLE stack is about 2 1/4 by 2
1/4 by 5 inches long.
</exit newbie info>
1.4 amp motors were common in old plotters and printers. The reason
is that most older inexpensive single chip(read cheap!)drivers were
limited to 2 amps.
In a type of drive mode called half step,1 then 2 coils are on and it
keeps alternating 1 then 2 coils,then 1,then 2...
This means the torque varies also. To smooth out the torque and make
the motors run more smoothly, the current is INCREASED whenever a
single coil(only) is on.
Turns out the best number to use for this is the square root of 2,
which is 1.414! So by rating the motor at 1.4 amps, we can boost the
current to our max of 2amps whenever only one coils is on, and drop
back to 1.4 amps whenever we have 2 coils on!
This so-called "modified" half-stepping was the norm when these older
plotters and printers were made. Micro-stepping was too expensive for
these run-of-the-mill products. And full stepping has more resonance
(misstep at certain RESONANT speeds)problems.
Another point when you're out shopping for surplus steppers. Most of
the older drives used Unipolar mode.(described in recent msg's)IT was
and is CHEAP! Many of the old motors have a high inductance which
will limit their top speed with today's common BIPOLAR chopper
drivers. How to tell?
Look for low volts, high amps when you're shopping. This will
GENERALLY be a low inductance motor and used with modern drives in
our typical uses will give best performance.
The older motors can: work fine,last a long time, don't rust, bust,
corrode or collect dust. But the newer motors ARE better, if you're
using the newer drives.
Ballendo
> The steppers are 3.8 amp at 1.4 volt and have 53 oz in hold.Bill, are you sure they're not 3.8 v ,1.4 A ?? Seems much more
> I realize that they are quite light but to start with <snip>
likely. Older plotter,53 oz. in.,etc. What size are they?
<Newbie info alert>
Step motor frame sizes are usually a number which relates to the
approximate distance across the MOUNTING face. Some standard sizes
are 11(about 1.1 inches across) 17 (about 1.7 inch) 23( about 2.3
inch) 34 (3.4 inch) 42 (4.2 inch). Mostly we use the 23,34,and 42
sizes. The 23 is sometimes called a 60 (size of face in mm's) and the
34 is sometimes called a 90 (size across mount in mm's).
A second term you will hear (referring to steppers) is "stack".
Usually single, double or triple stack motors are used. The rotor
inside the motor(s)is made longer in more powerful motors of a given
frame size. And a second or third "stack" of iron is used. A 23
single stack (which I believe Bill may have in his plotter) is about
the size of a 2 1/4 inch cube. Very commonly, an older motor this
size is about 50 oz. in. torque. (new motors use better magnets for
more torque in the same size) A 23 DOUBLE stack is about 2 1/4 by 2
1/4 by 5 inches long.
</exit newbie info>
1.4 amp motors were common in old plotters and printers. The reason
is that most older inexpensive single chip(read cheap!)drivers were
limited to 2 amps.
In a type of drive mode called half step,1 then 2 coils are on and it
keeps alternating 1 then 2 coils,then 1,then 2...
This means the torque varies also. To smooth out the torque and make
the motors run more smoothly, the current is INCREASED whenever a
single coil(only) is on.
Turns out the best number to use for this is the square root of 2,
which is 1.414! So by rating the motor at 1.4 amps, we can boost the
current to our max of 2amps whenever only one coils is on, and drop
back to 1.4 amps whenever we have 2 coils on!
This so-called "modified" half-stepping was the norm when these older
plotters and printers were made. Micro-stepping was too expensive for
these run-of-the-mill products. And full stepping has more resonance
(misstep at certain RESONANT speeds)problems.
Another point when you're out shopping for surplus steppers. Most of
the older drives used Unipolar mode.(described in recent msg's)IT was
and is CHEAP! Many of the old motors have a high inductance which
will limit their top speed with today's common BIPOLAR chopper
drivers. How to tell?
Look for low volts, high amps when you're shopping. This will
GENERALLY be a low inductance motor and used with modern drives in
our typical uses will give best performance.
The older motors can: work fine,last a long time, don't rust, bust,
corrode or collect dust. But the newer motors ARE better, if you're
using the newer drives.
Ballendo