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Author Topic: Relationship of Velocity/Accel to G0...  (Read 9700 times)

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Relationship of Velocity/Accel to G0...
« on: June 23, 2010, 07:19:45 PM »
First things first..... Newbie Alert (mach that is  ::)

Next things - mach/machine setup info:

Motors: stepper - keling klh260-60-4a (4wire motors)
Drivers: gecko - G203v
transformer output - 25vac (according to marris this is about optimum for mH of motors
power module - pmdx power module
PC: asus mainboard, pci parallel port, agp? video
OS: WinXP Pro version 2002 SP3
Mach: R3.042.040
kernel: 60kHz
Steps per unit (in): 2546.479
Velocity: 1377 ipm
Accel: 137.07162
Step Pulse: 5us
Dir Pulse: 5us
A axis slaved to X

Now for the issue.  Although the motor tuning dialog runs the motors smoothly and quietly to 1377 ipm the best that G0/G28 can accomplish is about 425 ipm.  Beyond that the motors growl, stutter, stop.  I have watched the "blended spd" number on diagnostic screen and whenever that number gets to about 600 or so the motors start the growl, stutter, and stopping.  Due to gear reduction and r&p drive the rpm is a bit more than the the ipm (ie. 425 ipm = 552.5 rpm).

I can imagine that the 1377 ipm is a "theoretical" max while the motor tuning dialog is "in control" nothing else is going on (no math, no graphics, ...)

I would have thought that the "real" top speed would have been closer to 600-800 ipm (50% or so) than a paltry 425 ipm (30%) given the motor tuning of 1377 ipm.

Where is the bottleneck?  It doesn't appear to be the drive system (runs at 1377 ipm or about 1800 rpm).  Before anyone asks, the motors are secured to a test panel not the actual machine (MechMate for curious minds).

Stan

Offline ger21

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Re: Relationship of Velocity/Accel to G0...
« Reply #1 on: June 23, 2010, 08:57:26 PM »
What's the processoe speed? If you open task manager, what's CPU usage when the motors stall?
Gerry

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

JointCAM Dovetail and Box Joint software
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Re: Relationship of Velocity/Accel to G0...
« Reply #2 on: June 23, 2010, 09:46:47 PM »
ah the one thing I neglected to document.... 2133 MHz according to drivertest.

I will check cpu utilization tomorrow.

Offline stirling

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Re: Relationship of Velocity/Accel to G0...
« Reply #3 on: June 24, 2010, 09:07:53 AM »
Can I just check on a couple of things because there's something not sounding quite right here...

Although the motor tuning dialog runs the motors smoothly and quietly to 1377 ipm
How do you mean? AFAIK you can't RUN the motors from the tuning dialog.

It doesn't appear to be the drive system (runs at 1377 ipm or about 1800 rpm)
Have I misunderstood or are you saying that you can ACTUALLY get your MOTORS to spin at 1800rpm?

Because if so, OK it's not a world record but it's certainly worthy of the group stages.

Online RICH

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Re: Relationship of Velocity/Accel to G0...
« Reply #4 on: June 24, 2010, 10:42:43 AM »
   Stan,
I could not find a motor curve for your stepper motor. You really can't use info from some similar motor, yes maybe ball park,
but not good.  The info on kelings site usualy gives torque to PPS ( pulses per second ). Note that that you need to know at what voltage and how wired to compare.
Here are some ball parks figures:
pps    rps  rpm
2000  10   600
4000  20  1200
6000  30   1800
10000 50   3000
I wouldn't think that you can get 3000 or even 1800 rpm from that kind of motor.
Now if at 4000 pps, you are probably at almost no motor torque, so max speed / no torque ....poor power.
"In a way" you could actual find the peak rpm , you just turn the stepper, letting it generate a voltage and see at what rpm  the max voltage occurs.
 Then to drive it at that rpm, your controller would need to be able to provide a signal of adequate quality and voltage, etc , but you would have no power.
So if you can get 1377 i see no value in that rpm, and would practicaly think that  it would a lot lower since you are using 25 volts.

Kernel speed is ok at 60k ( 1377x 2546/60= 58431 ). You could set the motor tuning to whatever you want, that dosen't mean in reality you will get there.
To get the high speed you probably need a higher voltage, thus your limited.

Since you don't have info to get a rough idea on what to expect, then, you will have what you have based on testing with it hoooked up to the machine.
Then additionaly other things will come into play and that 425 is probably not even a reliable ipm to be had.

FWIW, off to the sidelines,
RICH

Offline ger21

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Re: Relationship of Velocity/Accel to G0...
« Reply #5 on: June 24, 2010, 11:52:42 AM »
Quote
How do you mean? AFAIK you can't RUN the motors from the tuning dialog.

Use the up and down arrow keys.
Gerry

2010 Screenset
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JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline stirling

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Re: Relationship of Velocity/Accel to G0...
« Reply #6 on: June 24, 2010, 12:36:33 PM »
Thanks Gerry - never knew that - learn something new every day - that's Mach for you...

Ian
Re: Relationship of Velocity/Accel to G0...
« Reply #7 on: June 24, 2010, 02:28:52 PM »
I knew this was going to create a lively discussion..

But with the settings posted and using the motor tuning dialog, I can press and hold the up (or down) key for just about as long as I desire.  But any gcode command that yields a "blended spd" above about 600ish the motors crap out.  This is more so with a command such as g0 x.. y..  Please note that the motors do not immediately crap out.  It is usually well after the motors have accelerated and moving at top speed.  They usually just lock up and whine until Mach starts slowing down.

And yes at 1377 ipm the motors are going to have almost no usable torque.  These motors are 4wire so there is no choice in the wiring only a choice on the motor voltage (the 25v is the xformer output, the drive input is close to 35 VDC) and/or current (I forgot to say that the G203V current resistor is set to give 6amp/phase, yes they are heatsinked).

And I totally agree that even 425 ipm may be pie-in-the-sky when it gets on a real machine.... The specs I listed are what they are... They are not completely correct and wont be until they get on a real mount, running on a real machine (hopefully this will be in the next few weeks).  I just did not want any surprises on the machine and also wanted to stay cool a bit longer....

But why the BIG difference between what I can run the motors with the motor dialog vs gcode (especially G0 and G28)?  I have even noticed a change in the motor sounds when using a usb mouse with just wiggling (the mouse not me ;-)  AND changing the Feedrate while in operation (even down from 100ipm) can cause the motors to get rough.


More discussion as I really want to understand this....


Re: Relationship of Velocity/Accel to G0...
« Reply #8 on: June 24, 2010, 03:05:01 PM »
Got around to checking CPU utilization with Task manager.... CPU rarely got above 30% and motors crapped out on the motor tuning dialog.....

This is a Intel Core2 processor machine....

I'm still in the camp of overhead that may be present in normal mach operations that are not present in the motor tuning dialog.

Stan

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Re: Relationship of Velocity/Accel to G0...
« Reply #9 on: June 24, 2010, 04:25:35 PM »
 
Quote
I have even noticed a change in the motor sounds when using a usb mouse with just wiggling
- don't / quit playing  with your mouse    >:D  ;D.......what happens when you do the driver test and move the mouse around as i would bet that
  you will see a bunch of spikes, which are interuptions to the pulsing, which when doing that will screw up the pulse stream to the drives.
  Same for changing the feedrate.

Quote
G203V current resistor is set to give 6amp/
-what are the motors rated for...a stepper can behave rather koofy when the amp rating is too high ( trust me as i have four machines, different motors and need to switch the amp selection on the dirves for them to work correctly)

Quote
motor dialog vs gcode
 
Co-ordinated Linear Motion  (Section 10.1.5 in manual)
Co-ordinated linear motion - each axis moves at constant speed and all axes move from their starting positions to their end
                                               positions at the same time, also defined as control the axes so that, at all times, each axis has completed
                                               the same fraction of its required motion as the other axes
                                            - IE; any two axes ( x,y or z ) produces motion in a straight line
                                            - the motion can be done at prevailing or rapid feedrate and may default to the slower axis feedrate
 
FEEDRATE ( unless G93 is used ) Section 10.1.6 in manual
1. X, Y, Z  + A, B, C         - without simultaneous rotation -  F =length / minute  ( along the linear path )
2. X, Y, Z  + A, B, C         - with simultaneous rotation -       F =length / minute  ( for the XYZA combination linear path ~ modified F
                                                                                                                           based on a diameter)
3. X, Y, Z  + A or B or C  - with simultaneous rotation -       F= Degrees / minute of  A or B or C
3. X, Y, Z  + A B C                                                                  F= Degrees / minute  using a blended ABC / conceptual angular motion
                                                                                                        for total time


3 Feed Rate Modes - ( Section 10.7.25 in manual )
G93        - inverse time feed rate -            F = 1/F#  minutes ( if the F number is 2.0, the move should be completed in half a
                                                                                                   Minute) 
                                                                 - if active, an F word must appear on every line which has a G1, G2, or G3 motion
                                                                 -  an F word on a line that does not have G1, G2, or G3 is ignored.
                                                                 -  does not affect G0 (rapid traverse) motions.
                                                                    It is an error if: inverse time feed rate mode is active and a line with G1, G2, or G3
                                                                    (explicitly or implicitly) does not have an F word

G94        - units per minute feed rate         F= inches / minute, mm / minute, or degrees / minute, determined by length  units are being
                                                                         used and which axis or axes are moving

G95          units per rev feed rate                F= number of inches / mm / degrees per spindle revolution, determined by what length units
                                                                         are being used and which axis or axes are moving. 

RICH