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Author Topic: stepper motor speed  (Read 2637 times)

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stepper motor speed
« on: February 18, 2015, 02:31:19 PM »
Hello chaps.

I do not have any specs on the stepper motors that i am using and i dont know what
what speed they are doing when i am at a fast feed  (G0).

This is the question.
If I connect up an odometer to the shaft of the stepper what gcode can i
give it to make it go full speed.

Maybe a stupid question - but all suggestions are sincerely appreciated

regards from south africa

fred evans
think of the trees-- use both sides of the computer paper

Offline ger21

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Re: stepper motor speed
« Reply #1 on: February 18, 2015, 03:33:56 PM »
Quote
I do not have any specs on the stepper motors that i am using and i dont know what
what speed they are doing when i am at a fast feed  (G0).

The Velocity in motor tuning.
Gerry

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JointCAM Dovetail and Box Joint software
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Re: stepper motor speed
« Reply #2 on: February 19, 2015, 04:34:47 AM »
thank you -- do I just jack it up to say 1000 ?
can I jack it up to higher??

Do stepper motors turn at the set speed even when not loaded??
So if the speed is set at 1000 un loaded  and checked with a tach at 1000
when i put it under light load will is still try to run at 1000?
using this as a benchmark i am hoping to be able establish
the max load for this motor?
 
think of the trees-- use both sides of the computer paper

Offline ger21

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Re: stepper motor speed
« Reply #3 on: February 19, 2015, 07:11:00 AM »
Steppers don't run at any "set speed. THey have the most torque when they are not spinning, and torque decreases as rpm's increase.
Many factors can affect the maximum usable speed.
Acceleration rate. friction. amount of weight your moving. Voltage.
All can have an affect on maximum usable speed. Even the specs of the motors. Two different motors with different specs can have very different top speeds.
The only way to know what your maximum speed should be set to is with lots of trial and error testing.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: stepper motor speed
« Reply #4 on: February 19, 2015, 10:56:39 AM »
thanks Ger21

Perhaps what i mean is "if a stepper is set to run at a certain speed when unloaded
will it run at the same speed when a load is applied?" ( I realize that the motor could of course
be stalled if a high load is applied- but lets presume a low load which the particular
motor could quite easily handle - will it still run at the speed it was set at unladen?)
think of the trees-- use both sides of the computer paper

Offline ger21

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Re: stepper motor speed
« Reply #5 on: February 19, 2015, 11:16:20 AM »
It depends on the particular speed and load.
There'll be a finite speed that's dependent on the load.

The answer that I think you're looking for is yes, it'll run at the same speed. If the load is too great, the motor will stall. But it will not run at a slower rate once the load is applied.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: stepper motor speed
« Reply #6 on: February 19, 2015, 02:38:05 PM »
Thank you very much-- yes that answers my question.
 i tried to enter 1000 in the velocity "window"  on motor tuning and it will
not accept the 1000
it reverts to 686 while the graph is at its highest??
think of the trees-- use both sides of the computer paper

Offline ger21

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Re: stepper motor speed
« Reply #7 on: February 19, 2015, 03:40:42 PM »
That's because your at the limit of your pulse frequency. If you want to go faster, you'll need to increase the pulse frequency.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: stepper motor speed
« Reply #8 on: February 19, 2015, 03:50:24 PM »
or ... reduce the resolution of your micro stepping. (if applicable)

Offline RICH

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Re: stepper motor speed
« Reply #9 on: February 19, 2015, 04:03:14 PM »
A stepper is pulsed to make it rotate and the pulsing rate is related to the Kernal Speed you are able to use with your computer. Mach shares time with Windows, thus,the rate that is acceptable varies with different computers. So when you go to tune the motors, the Max Velocity may be resticted by the acceptable Kernal Speed. To find what is acceptable... run the Driver Test. Additionaly some drives may limit the amount of pulsing and that in return can limit the
the motors rpm.

A stepper at high rpm has very little torque. For what ever you are trying to do, just make note that it is so much more important for the stepper to run reliably for the task than have some fast motor rpm.

FWIW,

RICH