Hello Guest it is November 14, 2019, 12:52:53 AM

Author Topic: Galil/Mach3 stepper motor accuracy confusion  (Read 10029 times)

0 Members and 1 Guest are viewing this topic.

Offline bjr

*
  •  7 7
    • View Profile
Galil/Mach3 stepper motor accuracy confusion
« on: August 03, 2007, 07:32:46 PM »
Can someone please help me... I'm confused on this one:

I just received some info from Galil tech support, but there are lingering questions I have:

DMC-18x6 is only outputting step pulses. Once the steps leave the controller we really have no idea what happens to them. What this means is that the only limitation that the controller could have is the maximum frequency that this step train runs at, which for the DMC-18x6 is 6Mhz. Also keep in mind that the 6Mhz is the limitation for our steps, if the amplifier then takes those steps and microsteps then the maximum speed for the motor will be less then 6Mhz depending on the number of microsteps.

1) What is a "step train"?  Is it a microstepping amplifier that goes between the output of the Galil card and the actual stepper motor?  If so, where do I get this microstepping amplifier/device?  Seems like just Galil card/Mach3 combo alone will not do microstepping.

2) If I have a 0.45 degree stepper motor capable of doing 800 steps per revolution, and I employ microstepping with it, then does this mean I will get twice the accuracy of a 0.9 degree stepper motor?

3) How does the Mach3 software take into account and handle microstepping??  If the above is true, then it seems like Mach3 has nothing to do with microstepping and that microstepping is achieved through some kind of hardware device....

Please, if anyone (Brian?) can help, I would appreciate it.


Offline bjr

*
  •  7 7
    • View Profile
Re: Galil/Mach3 stepper motor accuracy confusion
« Reply #1 on: August 04, 2007, 03:58:55 PM »
Well, I can answer some of my own questions now - amazing how much I can learn by surfing the web.

1) The step motor I purchase will usually be mated (optionally) with a corresponding microstep driver.  This is nice, because it ensures that the two devices were tested and will work correctly with each other.  And I will most likely end up purchasing the power supply from the same folks.

2) Yes, I will get twice the resolution out of a 0.45 degree stepper over a 0.9 degree stepper.  By purchasing a 0.45 degree stepper, I've eliminated many of the el-cheapo junk brands out there... doesn't seem like a lot of companies make the 0.45 degree steppers.  Great way to narrow down the choices and keep my sanity.

3) Still don't know how Mach3 software will integrate and let me control the microstep driver that comes with the stepper motor, and how it will perform with 0.45 degree stepper motors.
Re: Galil/Mach3 stepper motor accuracy confusion
« Reply #2 on: August 04, 2007, 09:50:02 PM »
I'm wondering why you need to use .45 deg stepper?  You can buy a regular 1.8 deg stepper and a 1/16 micro step drive and you will have .1125 deg per step and will most likely cost less.

Mach3 puts out step and direction signals for the motor drives to use, either stepper motor drive or ac/dc servo motor drive.  The software doesn't do any type of micro stepping it is the drives job.   As long as the drive you have or are going to buy accept step and direction signals then Mach3 will run it fine.

Offline bjr

*
  •  7 7
    • View Profile
Re: Galil/Mach3 stepper motor accuracy confusion
« Reply #3 on: August 04, 2007, 10:35:01 PM »
Thanks for your reply.

I'm a little green when it comes to designing a micro milling machine (think really finely detailed waxes and engravings with a cutting area of at most 4X4X4" xyz)

I just thought that by going with a native motor that can do 0.45 degree steps (it was designed to do this), that the performance and accuracy will be better than a 1.9 degree motor driven with a 1/2 step.  I was under the impression that stepping modifies the signal, and depending on the quality of the step driver circuitry, may not be so accurate.

So the chain goes like this:

Mach3 -> Galli controller card -> microstepping driver -> stepper motor

I'm still hoping someone will help me understand how I can change the microstepping on the fly - is it through Mach3, a dip switch on the microstepping driver, a feedback loop from the microstepping driver to the Galli card, or what?????

Doesn't seem practical to build an entire workpiece at 1/64 step from start to finish.... I'd like to think I can remove some bulk material faster initially at 1/2 step then do the finer detail in the last stages of cutting.  Anyone?

thanks



Re: Galil/Mach3 stepper motor accuracy confusion
« Reply #4 on: August 05, 2007, 02:14:44 PM »
I don't know what max pulse rate is for a Galil card and Mach3.  But it doesn't make much difference if you run steppers at 1/4 micro step or 1/30 micro step as long as you can supply enough steps in one second you will have a some high rapids. 
On one of mine Bridgeport mills that I retrofitted with Mach3 it has a 200 step/rev motor with a 10 microstep drive with a 2:1 reduction and a 5 turn screw this gives 20,000 steps per inch and it does ~60 inch/min max travel speed this setup will give you  .00005 resolution with plenty of speed on a 4x4 machine. 

There is now way to change micro step resolution because the CNC software has no way to know when the drive changed from 1/4 to 1/16 or so.  And there is no need for something like that. 

Take a look at some of the videos here:
http://www.romaxxcnc.com/video.htm#

I'm pretty sure they are running mach3 and I would say that is plenty of speed for 99.8% of the projects and people.

So do you want your machine to be very fast or very accurate?   With the Galil card you have it will be both and then some.

Offline bjr

*
  •  7 7
    • View Profile
Re: Galil/Mach3 stepper motor accuracy confusion
« Reply #5 on: August 05, 2007, 05:38:17 PM »
Thank you very much for your input. 

I see that I need to figure out how my machine will operate with the stepper motor, driver, ball screws and linear guides.

I'm amazed that you can achieve an accuracy of 0.0005" .... that's half a thousandth or just over 0.01mm!   Did you do anything special to your bridgeport setup to eliminate any linear deviance in the x,y,z planes? 

Thanks for clearing that up about the microstepping.... I really need to start looking at the total system components and how they will work together... at the moment I don't know how to calculate the amount of travel per microstep. 

Regards
BJR