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Author Topic: The Need For Speed. . . . At least for rapids  (Read 7402 times)

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The Need For Speed. . . . At least for rapids
« on: January 07, 2009, 12:17:15 AM »
I can cut plywood, maple and MDF very consistently at 30 IPM without any lost steps, but I would like to run rapids faster.

What can I do to increase my rapids speed, without risking loosing steps?
With the below settings the maximum IPM is 93.78, no matter what number I plug in above that it defaults to 93.78.  What is limiting this speed setting?

I noticed when running the X axis (x5, x0) it would run in the + direction just fine at 93.78, but as soon as it reversed it would stall.  Hmmm any ideas why?

Even after running over a half hour the motors are just warm to the touch, never hot.  I read about everyone being concerned about hot steppers and wonder why mine don’t get hot, hey not that I’m complaining, but why not?

Hager ???

Here are my specifications:

PC running XP Pro

Steppers: 200 Oz In
   Nema: 23
   Phase: 1.5 Amps
   Volts: 12-24
   6 wire Unipolar or Bipolar (wired as Unipolar)

Power Supply: 24V
Acme Screws: ½” 10 TPI
Steps Per: 16,000
Kernel Speed: 25,000
G’s: 0.0259019
Step Pulse: 0
Dir Pulse: 0
Mr. Chips
Retired 3M'r
Re: The Need For Speed. . . . At least for rapids
« Reply #1 on: January 07, 2009, 12:38:43 AM »
The maximum speed you can enter into the motor tuning dialog is limited by your kernel speed, which is the fastest rate at which the CPU can output step pulses.  If the driver test says you must run 25kHz kernel speed, then what you've got it what you've got, and you can speed it up only by either getting a faster PC, or buying a SmoothStepper.  On most PCs, 45kHz seems to be the practical limit on kernel speed, so at best you are likely to do no more than almost double your speed, without a SmoothStepper.

ray L.
Ray L.
Re: The Need For Speed. . . . At least for rapids
« Reply #2 on: January 07, 2009, 12:42:31 AM »
Is "SmoothStepper" a brand name?

Can I just change the kernel speed and try it?

Why don't my steppers get hot?

My Processor is 3.07 Gigahertz Intel Celron
Bus Clock 133 Megahertz

What should the PC numbers be to get more speed?

« Last Edit: January 07, 2009, 12:49:11 AM by Mr.Chips »
Mr. Chips
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Re: The Need For Speed. . . . At least for rapids
« Reply #3 on: January 07, 2009, 03:00:09 AM »
SmoothStepper is an external motion control card that connects to Mach over USB. It can pulse up to 4MHz and has a nice clean pulse so can often run motors faster than the parallel port can.

Yes choose 45KHz and try it, you will need to returne your motors.

Steppers dont always get hot, depends on how much current they are getting and how much use they are being put to. For speed voltage is what you want and for torque its current but obviously there are limits to both and your drives and motors types will determine what your safe max will be.

Your computer question is not so easy to answer, basically the faster your computer with more memory the better it SHOULD be but there is no guarantee as not all computers are made equally ;) Your computer should be more than capable of running 45KHz kernal so dont worry unduely about that.

Offline simpson36

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Re: The Need For Speed. . . . At least for rapids
« Reply #4 on: January 07, 2009, 07:27:27 AM »
As others have said, your speed is restricted by the kernel speed. I'm running 20,000 steps and the same total screw lead as you. With 25k and I max out at 75IPM, which is consistent with your results.

However, the stalling is a differnet problem. First off, you don't have enough voltage in your supply. Voltage should be many times the motors rating. I know it seems odd, but s that's the way it works. Probably why your motors don't get warm. Do some homework on steppers. www.geckodrives.com has a lot of good info and calcs. You can determine if your small steppers are up to the task. This is a somewhat complicated topic which requires some study (I'm still learning).

You need to look at the acceleration. If you have it set too high, the motors will stall trying to get the mass moving, which is especially demanding during a direction reversal. Raising the speed increases this problem.

Incidentally, your computer should be way more than enough for Mach 3. Currently I am using an old Intel P3 850mghz. It is a dual processor machine, but the CPU runing Mach never goes above 25% CPU utilization. On the other hand I was using a 1.2Ghz laptop wiuth a VIA processor and it was often pegged, so obviously processor brand type does have a lot to do with it.

You might want to confirm you are using the correct pulse width.
« Last Edit: January 07, 2009, 07:41:48 AM by simpson36 »

Offline ger21

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Re: The Need For Speed. . . . At least for rapids
« Reply #5 on: January 07, 2009, 11:12:50 AM »
Instead of changing the kernel speed, you can also change your drives from 1/16 stepping to 1/8, which would allow you to set your rapids twice as fast. But as was mentioned, if you're already stalling, you have other issues. Different drives that will let you use higher voltages will give you more speed. But an even better option is to change your screws to 2 start or even 5 start. You may be underpowered for 5 start screws, but 1/2-10 2 start screws may double your speed without any other changes.

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Offline simpson36

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Re: The Need For Speed. . . . At least for rapids
« Reply #6 on: January 07, 2009, 12:02:22 PM »

Quoting from that document, "The power supply voltage should be between 3 to 25 times the motor's rated voltage. If less than 3 times, the drive may not operate smoothly and motor heating is excessive if it is more than 25 times the motor's voltage."

Unless there is something I've missed (quite possible) higher voltage will not overcome the limitation imposed by the frequency, however, it would appear that low voltage definitely will prevent the motors from performing anywhere near where they should.

I am running both 4v and 2v steppers off a 36v supply and I can tell you there is a significant difference in the  . .  shall we say 'enthusiasm' of the drives.

In the case of Gecko, some have settable step size, but my 203v do not. As I understand it from Gecko's documentation, the drive's output starts at 10x and varies automatically up to full step depending on the speed the stepper is moving, but they always take a 10x input.
Re: The Need For Speed. . . . At least for rapids
« Reply #7 on: January 08, 2009, 12:00:18 PM »
Hi, Just read your question. The main thing that comes to mind is that you have your steppers wired unipolar. If you want speed, bipolar is a must. You'll get far more torque at much higher revs.

24v power is not the problem although as Simpson36 suggested, 36v would get more grunt at top revs.

As for hot motors, A stepper motor is at it's best when it is comfy warm to the touch, meaning you can hold the stepper body in your hand for 30 seconds or more. If your first impression is "Ooh, that's warm" and let go quick then it's too hot. Cool running steppers are OK but are probably not working hard enough and would benefit with more current supplied. Be sure to do the warm check when the steppers have been doing at least an hours work and not just sitting idle as some drives reduce the current to the steppers at idle.

No amount of software tweeking will get unipolar wired steppers to achieve anything like you should expect from bipolar wired steppers.
If you can change the configuration easily, you will probably need to alter the current limiting resistor on the drive.

Re: The Need For Speed. . . . At least for rapids
« Reply #8 on: April 21, 2009, 02:46:43 AM »
I started to use Mach3 3 days ago which downloaded from Artsoft.
I want to make it faster. Kernel Speed is 25000, I choose 45000, set it,  but my speed doesn't cahange.
What can I do for it ?
My mach 3 is a trial version. This may be the reason ?
- Seda -
Re: The Need For Speed. . . . At least for rapids
« Reply #9 on: April 21, 2009, 03:08:08 AM »
Did you change the speed in your Motor Tuning for the X Y and Z axis?
Mr. Chips
Retired 3M'r