Hello Gene,
On 7/14/20 12:49 AM, Gene Heskett wrote:
On Monday 13 July 2020 22:44:37 R C wrote:
well, I can calculate what the speed needs to be, also I can actually
"observe" it too.. by pointing the telescope at a star and see how
much the deviation is. I have encoder to check the actual speed of a
shaft.
I found some information in a manual/tech-sheet that comes with the
drivers, so I am trying to figure out what the best stepping rate is
and what the best way of actually sending pulses to the stepper-driver
is.
I wrote some c-code that runs the motors in pthreads, I just want to
know what the best way is. pulse lengths, pause/gap length etc.
(basically the best way to use a dm542 (all those steppers are sorta
the same I understand)
The driver tech-sheet basically says it can do pretty all it's
available micro stepping with a 1.8 degree stepper motor, I wonder if
that is really true.
In theory yes, in practice, no. There is resistor tolerances and all
sorts of errors that can creep into a motor being held by the relative
balance of the currents thru 2 sets of coils. So while a full switch
will move it 1.8 dgreees, or 1.2 with the newer 3 phase models, between
magnetics and parts tolerances, half current in each coil might be out
of balance as much as 10% in off the shelf stuff. Sometimes its fairly
obvious, I have a dm860 driver that when moving a 1600 oz/in motor at
a /8 divisor, moves 7 steps rather noisily, and the 8th step cannot be
seen or heard. Worked fine on my mill as long as I stayed below 26 ipm.
But thats too slow for rigid tapping. A 960oz/in and ac powered driver
was subbed, moves that heavy head at nearly 100 ipm, dead smooth.
Right, but I can probably get it close by calculating, and then adjust
for "tolerances" and
feedback from the encoders I have.
I also have a dm860, using it in a Sherline mill where I put a bigger
stepper motor on the Z-axis.
(I replaced all stepper motors and drivers in a Sherline mill and lathe
(they came in a Paxton/Patterson enclosure).
thanks,
Ron
Ron
On 7/13/20 8:35 PM, Chris Albertson wrote:
A fast control loop that drives each motor at a given speed and a
second slower control loop that figures out what that speed should
be. The second loop typically uses "PID" even if only in fact the
"P" is used.
That can be used to drive any number of motors all at their correct
speeds.
On Mon, Jul 13, 2020 at 7:28 PM R C <cjv...@gmail.com> wrote:
Interesting,
but I already have the motors, and the gears are on their way.
What I was really looking for is how to drive the stepper-drivers,
he DM542 series ones.
Ron
On 7/13/20 7:53 PM, cogoman via Emc-users wrote:
I recently discovered geared stepper motors.
http://www.zyltech.com/nema-17-stepper-motor-geared-planetary-gearb
ox-1-7-a-3-1-nm-435-ozin/
I've been happy with zyltech in the past. I bought one of these
for evluation, but the specs seem to be great for CNC. Low enough
current to work with a stepstick, High enough torque for a fairly
powerful machine, and less than 4 mH inductance should let it step
pretty fast.
5.18:1 gear ratio should reduce that 4 meter spur gear, but the
link below has higher gear ratios that would reduce that spur gear
greatly! Backlash could be a problem for CNC, but if you are only
going one way, the less precision gearboxes might be fine.
https://www.omc-stepperonline.com/geared-stepper-motor/?sort=p.pric
e&order=ASC
Once you visit the stepperonline web page you know as much about
them as I do, but their offerings might be just right for your
application.
On 7/9/20 2:23 PM, R C wrote:
Hello,
this is (probably) off topic, been seen that happen. If it is
please ignore it.
I am building a "motorized" telescope mount (dobsonian) with
what is called an equatorial platform, it has 3 axis which I am
going to drive with stepper motors.
The stepper motors I use with a stepper driver, those common
DM542 ones, the stepper motors themselves are 2A and 1.8 degrees
per step.
What I want to accomplish with the equatorial platform) (it
compensates for the rotation of the earth) is that, the start
and end position accuracy is not that important, smooth and
constant/consistent movement is. for the azimuth/altitude
precision is not a really big deal, but you'd want to move these
2 axis somewhat swift.
So there are a few factors to decide.
I probably want micro stepping, what settings on the driver for
pulses per rev, is best to use (or is that just trial and error?)
As with PWM itself, I am probably just not too familiar with it.
From what I understand, the voltage I use for the motors
determines how fast I can go (I am going to use a 48V switching
power supply).
as for PWM, I can of course change the length of the pulse
itself and, independently, change the time between two pulses.
What is the relation ship there? WHat does a longer width of
the pulse itself do? and what exactly does a longer gap between
the pulses do (of course the wider the gap between two pulses the
slower the motor turns).
for, especially, the equatorial platform, I want to avoid
"jerking" it, meaning starting and stopping the stepper motor
as little as possible and just go at a 'slow' constant speed.
sorry if totally of topic....
thanks,
Ron
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Cheers, Gene Heskett
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