Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: rrc1962 on November 25, 2009, 05:06:38 PM

Title: Motor tuning
Post by: rrc1962 on November 25, 2009, 05:06:38 PM
I have an interesting issue.  With speed in motor tuning set to 800IPM I can job the machine easily at that speed, but when I issue a G0 command the motors stall toward the end of the path.  I can only get 300IPM reliably from a G0 command.  The machine is a plasma table with steppers.  I was tinkering earlier and moved the pulse and direction pulse width up to 4 and it ran great at 600IPM on a test file, then after a hour or so I went back and tried running the same file and the motors were stalling again.  300IPM seems to be the magic number.  I just can't quite figure out why it will jog at 800IPM all day long but won't rapid from G code at more than 300IPM.  The acceleration settings didn't even make much difference.  Motors were still stalling set at 600IPM and an acceleration of more than 1 second.   At 300IPM I can set the acceleration to .05 seconds with no problem.

Is there something I'm missing or should I just be happy with 300IPM?
Title: Re: Motor tuning
Post by: Chaoticone on November 25, 2009, 06:33:23 PM
How many RPM are you turing at 800 IPM? What are your steps per? What is you gearing? What hardware are you using? Parallel port? Smooth Stepper?

Title: Re: Motor tuning
Post by: rrc1962 on November 25, 2009, 09:27:04 PM
Steps per inch are 3750 figured after the reduction of 5:1.  It's running through the parallel port.

I had not figured out the RPM, but if my math is correct, that's probably the problem.  In the past, I've noticed that steppers seem to hit a wall at about 1000 RPM.  In my case, I'm moving .540 per revolution.  800 / .540 = 1481RPM.  Please correct me if my math is wrong.  I'm zoned out on decongestants.

Perhaps I'll try dropping to a 3:1.  That should bring the steps per down to 2250.  That should bring the RPM at 800IPM down to about 900RPM, provided the increased torque isn't an issue.  At the very least I should be able to get the speed up to 500IPM.  500IPM at 3:1 is about the same RPM as 300IPM at 5:1.

Just out of curiosity, would a smoothstepper overcome this RPM limitation?
Title: Re: Motor tuning
Post by: Chaoticone on November 25, 2009, 11:20:51 PM
The Smooth Stepper will help if your trying to push more pulses than what you PC can reliable pulse.  You can set Mach to pulse up to 100KHz (100,000) pulses per second but your PC being able to go that high may be the issue. The Smooth Stepper can pulse over 4,000,000 (4MHz) times per second. It also reduces the load on your PCs processor. 3750 steps per at 800 IPM is 50,000 pulses per second or 50KHz if my math is right. So, if the pulses are the bottle neck, the smooth stepper could be your answer. If the Stepper RPM is the problem it will not help that at all.

Title: Re: Motor tuning
Post by: RICH on November 26, 2009, 07:40:15 AM
There are a number of things which affect the tuning of a stepper and are related as to how they will behave.
Take a look at the the first few posts in the link below where I look at steps/unit, motor speeds, torque at different speeds, to anticipate what would be acceptable settiNgs based on on some information and what you plan on doing with your machine.,12484.msg80823.html#msg80823

Title: Re: Motor tuning
Post by: rrc1962 on December 02, 2009, 09:45:32 PM
Just thought I update.  I was hitting wall with the pulse rate.  I figured that because when it stalled, everything stalled, not just the motor that was moving fast.  I tried upping the pulse rate but that didn't help, so I'm guessing it's a hardware limitation.  Anyway, I dropped to a 3:1 reduction and can now rapid all day at 500IPM with an acceleration of 30.
Title: Re: Motor tuning
Post by: Chaoticone on December 02, 2009, 10:13:52 PM