On 7/14/20 11:48 AM, John Dammeyer wrote:
-----Original Message-----
From: Chris Albertson [mailto:albertson.ch...@gmail.com]
Sent: July-14-20 2:49 AM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor
Gene is correct when he wrote the precision might be off when
micro-stepping.
Yes. Micro-stepping is only for harmonic reduction. You cannot rely on
positioning with micro-stepping. It can take 3 or 4 micro-steps to even start
moving to overcome static friction.
Motors are mechanically built for 1.8 degree steps so that is likely to be
accurate but half steps depend on the driver.
Half steps rely on only one coil energized so you lose half the torque. For
static motion that may well be enough depending on the size of the motor and
the load.
But what I wanted to add is that when you read the speed vs. torque curve
it is for FULL steps. The amount of holding torque is reduced with
microsteps. It makes sense too, full steps use full current that is
switched between coils just 100% on or 100% off. With microsteps one
coild gets perhaps 3/8 of full current and the other gets something like
5/8. So the current is overall reduced.
70.7% is the number you are looking for.
In any case, run the motors at a step rate that causes them to run smoothly
without actually stepping. You want to see continuous motion.
BTW I'm using a DM542, the same driver you have on this vertical axis test
(link below). It has enough power even when doing 1/2 steps to move a 35
pound chunk of steel up and up at a decent rate of speed. machine is
obviously not balanced like a telescope The DM542 is set for only 2.0 amps
so it is not running at full power. SO you will be fine even with the
reduced torque.
This is the first time this axis ran. Just some jogs up and down.
https://youtu.be/tlMTksuOuZQ
Were you using LinuxCNC for this? Or did you write your own control software?
Actually, both. I have a Sherline mill and lathe that I am running
with lnux cnc and... the same motors and stepper drivers.
The telescope will have the same drivers and stepper motors, BUT
writing my own interface to try and control them,... well that before I
try to hook it up to Stellarium directly.
John Dammeyer
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