I seriously just might take him up on it if you don't. It DOES sound
like a fairly powerful stepper, and that's what I'd like to use for the
tilt on the camera pan-/tilt-head I'm trying to develop. (I've already
got the pan part ready to go. Thanks, folks, but don't try to sell me a
"pre-built" kit - I know that such animals already exist, but I'm doing
it from the "scrounge-pile" purely for the sheer "Am I able to make it
happen?" of it - call it a self-administered, self-graded "Final Exam"
in computers/electronics/robotics/scavenging/MacGuyvering
)
A couple-few questions for Rich, though -
1) I know an inch-ounce is the force the pivot will see if an ounce of
weight (assuming we're at 1 earth gravity) is placed on a 1 inch lever.
And a ft-lb is the force of a pound of weight working against a 1 foot
lever. So can someone check me here? (300In/Oz) / 192 (12 inches to a
foot times 16 ounces to a pound = 192In/Oz per ft/lb?) = about 1.6
ft/lb? Or have I got the conversion hopelessly screwed up?
2) Is this 300 in/oz/1.6 ft/lb measured directly on the motor shaft, or
is this after a reduction package, and if reduction, is the geartrain a
worm, pancake type, or maybe even a combination of both?
3) How many phases (I'm assuming 4) and control wires? (Assuming 6) and
are the phases tagged, or do I have to play "What happens if I energize
in this sequence?" to find out?
4) What's the step angle per phase?
5) If it's supposed to be 3.1V@4A, got any suggestions for how I should
expect it to behave if I were to try to power it from a
[email protected] supply?
How about
[email protected]? (Besides the most intuitive "All the smoke will
probably leak out - whether it leaks out of the PS or the stepper is
questionable" scenario - IF there's a viable alternative - right now,
those are the flavors of juice I can supply easily. Hmmm... brainstorm
just hit: I've got multiples of that PS - Do SMPSes parallel OK? That'd
give me 5V@5A that I could mess with regulating down to 3.1V if I
absolutely have to.)
6) (And last - I think) What kind of physical dimensions and weight on
this unit? Shaft size? Length? Splined, smooth, or geared? Gear or
spline pitch/tooth count (if applicable)?
7) (This is really last) How many do you have/want to get rid of?
haha, OMG, you ARE serious! Half the stuff I don't know what you're even
talkin about! =)
Jase
[/QUOTE]
All but #1 and #7 are fairly important things to know about a stepper's
capabilities, with #s 2, 3, 4, and 6 being the most critical for
figuring out which one to use in your application.
#2: Torque - 300 inch-pounds of holding torque means that it will keep
300 ounces (A bit less than 19 pounds) of force from moving a lever one
inch inch long, assuming the lever pivots on the stepper's shaft. A
stepper with only 1 inch-ounce of holding torque isn't very strong at
all, and will probably not be worth trying to use for turning anything
heavy, or anything that needs tobe held to a tight positioning against
some outside force acting on it, since a fart from across the room just
might be enough to break its step. A "weak" stepper can, in effect, be
made "stronger" by having it drive a reduction geartrain, so that the 1
inch-ounce unit driving a 16:1 reduction could hold position against a
pound of force being applied to that one inch lever, instead of an
ounce. The tradeoff is, of course, speed - It's now going to take 16
turns of the stepper shaft to get one turn of the output shaft of the
geartrain, or 16 steps of the stepper to get one step worth of rotation
at the output shaft of the reduction package. Worm-and-wheel, and
"pancake" style gears are two construction methods for reduction units -
Each has its plusses and minuses that are *WAY* off topic for an
electronics newsgroup, and beyond my abilities to explain, besides.
#3: Phases/control wires - Steppers come in various "flavors" - 2 and 4
phase being most common, though others exist. Phase count influences #4
(step angle) #2 (holding torque) and wiring - A two phase stepper
probably has either 3 or 4 wires to connect, and wil have a difference
stepping sequence than a 4 phase unit. 4 phase probably has 6 or 8 wires
that need to be connected, and in both cases, one needs to know the
stepping sequence to make the stepper do anything other than sit there
and twitch spastically. Energizing one phase of a stepper results in it
taking exactly one step. Energizing the next phase in the step sequence
makes it take another step, etc, so to get it to turn, rather than
wiggle, you repeatedly energize the phases in the step sequence.
Figuring out the step sequence from a handful of wires and the info on
the stepper's nameplate can be... "interesting". "So I need to step it
as phase1, phase3, phase2, phase4 to get it to turn clockwise - OK,
which pair of wires is phase1? Repeat for phases 2-4. Now did I get the
polarity right? (IE, I've figured out that Black and Red are phase1, but
if I put the juice to it as red(+) and black(-), it steps clockwise, and
reversing the polarity makes it step counterclockwise)
#4: Step angle: How far does the shaft turn for each step that happens?
1.8 degrees per step is very common, but other angles are possible -
I've encountered 180 degrees per step units, 3 degrees per step, etc -
*LOTS* of possibilities. #3 (Phases) usually has a big impact. Smaller
step angles usually mean higher holding torque (but not always) and more
phases usually mean smaller step angles (but again, not always) Smaller
step angles ALWAYS mean more positioning precision is possible.
#5: Power requirements - Too much, and all the magic smoke leaks out of
something (maybe the power supply, maybe the stepper, maybe parts in
between) Too little, and the stepper doesn't do much of anything.
There's a "happy medium" to be found for each one. The one Rich is
talking about wants 3.1 volts at 4 amps. Volts and amps can be "fiddled
with" in various ways to make it possible to apply more amps and less
volts, or more volts and less amps, or some combination, to let you feed
the beast with what you've got. But there are limits before the smoke
leaks out.
#6: Physical properties - "Will it fit where I want to put it? And if it
will, can I get it mechanically connected to what I want it to drive?"
It's more than a bit difficult to mate a round-with-a-flat shaft to a
driven gear, ferinstance, and trying to fit a smooth round shaft to a
splined input is probably going to work about as well as a lead balooon.
Hope this helps...