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Author Topic: Stepper Speed Factors?  (Read 6940 times)

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Offline Fastest1

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Stepper Speed Factors?
« on: February 09, 2011, 08:34:46 AM »
I have been running a few small machines with Mach 3 over the last year or more. My latest is a Dyna DM2400 with a gear reduction on each screw (not what I wanted necessarily but that is what it came with and it is very accurate). Anyway I have my kernel speed on 25000Hz. My acceleration and velocity are acceptable with no loss of steps. I run a 48v 12a power supply and a gecko g540. My cutting speeds are in the 12 ipm range and might max out at about 13.5 ipm even using a feedrate override. What are all of the factors controlling speed? If you use a wizard in Mach 3, it will show a materials page. On this page if you select aluminum for example, there is a feedrate box. Is this box responsible for max speed in that material? I usually use the above 12 ipm for cutting in aluminum but would like to play around with higher speeds, feedrate increased to 290% still only achieves 13.5 though the base feedrate was 12 ipm. No interest in new equipment, smoothsteppers or other stuff just optimizing and understanding what I have. Btw my steps per unit are in the 10160 range due to the 10:1 reduction. What would be my calculated max speed with those settings? Ideas.
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

Offline Hood

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Re: Stepper Speed Factors?
« Reply #1 on: February 09, 2011, 08:50:02 AM »
Even if you define a faster feed rate Mach will not go above the Velocity you have set in Motor Tuning so I am guessing 13.5IPM is what you have there.
Hood

Offline Fastest1

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Re: Stepper Speed Factors?
« Reply #2 on: February 09, 2011, 10:34:23 AM »
Hood, I cant imagine how many times I have thanked you but by now, I need your address for a Christmas card to say the least. Anyway i played with the velocity and it was as you said @ 13.5. I was able to tune up to about 18-20 ipm max and it seems best if the g's end up around .01 vicinity. I also misstated the kernel speed, I am tuned to 35000Hz and not missing steps or wasnt prior to changing the velocity settings a minute ago LOL. Oddly enough my Z was able to tune to the highest ipm's and all 3 steppers are the same as is the gear reductions, ? Is there any reason to have these speeds matched on each axis in regards to timing? Is the only way to increase my speed by raising the kernel speed? Ok just looking back at my tuning (when I posted I wasnt at my machine), I am running 101600 steps per unit inches in my DM 2400's case. Due to my reduction am I at my max? The velocity slider would only allow a max of around 20. Wow, I just opened another machines xml. 1 for my A2ZCNC Sherline and it is running 25000Hz but only needing 1600 steps per unit. I use 60ipm there but could slide the velocity into the 967ipm range (theoretically as I didnt bother to test it that high). I am not sure of what speeds this little machine can handle, seems like Jeff Birt claims in the 30-40 ipm with a smooth stepper. If I am at the max at this kernel speed, wouldnt a higher kernel speed allow more commands per second? I am sure there are many other factors too.   
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

Offline Hood

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Re: Stepper Speed Factors?
« Reply #3 on: February 09, 2011, 11:03:00 AM »
The kernel determines how many pulses per second can be output as a maximum, setting the kernel higher than you can get from a motor will likely not help things and may actually make your computer unstable, so if you find that your motors top out before the max allowable at 35KHz then there is likely no advantage to setting it higher.

Hood

Offline Fastest1

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Re: Stepper Speed Factors?
« Reply #4 on: February 09, 2011, 11:26:15 AM »
Does a smooth stepper some how work around this? Or is there something else at play?
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

Offline Hood

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Re: Stepper Speed Factors?
« Reply #5 on: February 09, 2011, 11:31:05 AM »
SmoothStepper has a very nice uniform pulse which may help you achieve more speed but that will depend how good the pulse is from your particular computer.
 On my Bridgeport the SmoothStepper didnt let me get any increases, the motors sounded smoother and much nicer but thats all.
On my lathe and Beaver mill however it made a big difference but that was not due to the smoother pulse but rather because these machines have AC Servos with high count encoders and the parallel port can not pulse fast enough even at 100KHz to top out these motors.
Hood

Offline stirling

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Re: Stepper Speed Factors?
« Reply #6 on: February 09, 2011, 12:09:44 PM »
Hi Fastest1 - What Hood said - but also I think maybe you're looking at it the wrong way round. The speed your motors can achieve in terms of revs/min is primarily determined by the motors, the drivers and the power supply. Mach must then use a kernel speed that most appropriately allows it to provide whatever pulse speed is neccessary to achieve that. So whilst "capping" Mach's kernel speed too low will prevent your motors from reaching their potential, increasing it above their potential is pointless.

So for example: If your motors run fine at 20 inch/min (101600*20/60 = 33,866 Hz) then the 35KHz kernel is the one to use. If however, you decide that they're more stable and therefore set your max of 13.5 inch/min in motor tuning (101600*13.5/60 = 22,860 Hz) then the 25KHz kernel is the one to use and the 35KHz kernel would then be pointless.

Ian

Offline RICH

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Re: Stepper Speed Factors?
« Reply #7 on: February 09, 2011, 12:55:16 PM »
Fastest1,
1. The most reliable Kernel speed is 25000HZ. Hood posted a nice write up by Art on the matter some time ago. Kernel speed can limit your vlecoity
and you can easily see the effect just by changing the kernel Speed to something higher and noting how how much more you can increase the velocity in motor tuning. That dosen't mean nothing if the system can't take advantage of the higher kernel speed.

2. Machining metal - There are general recomended speeds and feeds based on historical testing and also studies that have been done over time.
    What is recomended is based on chip load, spindle rpm, coolant type, cutter type , cutter material, etc and then basicaly you can derive the    hosrepower required to accomplish the machining, Of course surface finish and other things come into play.
So what i am saying is that even if you can use a high kernal speed to up the IPM it may not mean nothing if the increased speed is not applied
appropriately to what you want to machine.

3.Given some set of conditions ,such as torque to speed as defined by a motor curve, the electrical conditions such as how motors are wired and available voltage, etc can have a big affect on velocity / feedrate of the axis.

In summary, 1,2, 3 above are all interelated and one needs to keep each in perspective.  

FWIW,
RICH


Offline Fastest1

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Re: Stepper Speed Factors?
« Reply #8 on: February 10, 2011, 11:54:50 AM »
I appreciate everyones responses. I am not looking for really increasing the speeds to anything unreasonable just at times it would nice to bump it more than 10% of its feedrate. In aluminum I seem to be able to pocket at .05 doc with a .250 4 fem at 12ipm, I believe there are conditions that would allow a higher feedrate, I could go for a deeper doc and leave the feedrate as is possibly. Just looking at any kind of gains as always. Thanks
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

Offline kf2qd

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Re: Stepper Speed Factors?
« Reply #9 on: February 10, 2011, 04:27:59 PM »
The biggest limitation on you speed with that machine is caused by the gearing. The ration is so high that you are spinning the motors somewhere near their max RPM If you want highewr rappid moves you could change teh gearing to a lower ratio and gain speed for rapid moves. There would be some loss of torque, but at the ratio you are using that probably not be a problem.

Another question - Are you Microstepping? At the number of stepps you are currently running you could turn off microstepping, change teh number of stepps per unit to match the new setting and use that to  run at a higher speed.

at 100,000 steps+ per unit you have a lot of resolution that you probably can't use.