Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: StanLewis on June 23, 2010, 07:19:45 PM

Title: Relationship of Velocity/Accel to G0...
Post by: StanLewis 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

Title: Re: Relationship of Velocity/Accel to G0...
Post by: ger21 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?
Title: Re: Relationship of Velocity/Accel to G0...
Post by: StanLewis 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.
Title: Re: Relationship of Velocity/Accel to G0...
Post by: stirling 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.
Title: Re: Relationship of Velocity/Accel to G0...
Post by: RICH 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
Title: Re: Relationship of Velocity/Accel to G0...
Post by: ger21 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.
Title: Re: Relationship of Velocity/Accel to G0...
Post by: stirling on June 24, 2010, 12:36:33 PM
Thanks Gerry - never knew that - learn something new every day - that's Mach for you...

Ian
Title: Re: Relationship of Velocity/Accel to G0...
Post by: StanLewis 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....


Title: Re: Relationship of Velocity/Accel to G0...
Post by: StanLewis 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
Title: Re: Relationship of Velocity/Accel to G0...
Post by: RICH 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
Title: Re: Relationship of Velocity/Accel to G0...
Post by: ger21 on June 24, 2010, 06:08:35 PM
What if you do G0 X500? You should get a blended speed over 600 with one axis moving. Dos it still do it?

If it does, try 35Khz mode. And get a PS2 mouse.
Title: Re: Relationship of Velocity/Accel to G0...
Post by: StanLewis on June 24, 2010, 06:36:27 PM
dang it I WANT TO PLAY WITH MY MOUSE   >:D  Seriously when I went back to a ps/2 mouse the motors were slightly better.  Again points to load/overhead....

Motors are rated at 6A/phase, yeah I've seen steppers get flaky when underdriven but really flaky if overdriven (current more so than voltage).

What is the default feedrate mode?  This is a simple gantry with A - angular unchecked and slaved to x.

Start installing these on the machine..... probably tonight  :)

Stan
Title: Re: Relationship of Velocity/Accel to G0...
Post by: StanLewis on June 24, 2010, 06:39:00 PM
Sorry,  If I do a G0 X500 the motors complain a bit.  I have the feed rate override set to try to keep the G0 from running off the highend, otherwise the motors are going to complain big time..

Even if I reduce both velocity and accel in the tuning dialog to a more reasonable 425ipm which I know they will run.

Stan
Title: Re: Relationship of Velocity/Accel to G0...
Post by: ger21 on June 24, 2010, 07:45:56 PM
So if you set the velocity in motor tuning to 425, and do a G0 X500, the motor will still stall? What's the accel set to?
Title: Re: Relationship of Velocity/Accel to G0...
Post by: StanLewis on June 25, 2010, 07:24:43 AM
maybe I didn't set the accel low enough... when velocity set to 425 and accel to 42 (10%) then G0 problem still occurs..

Now I have found that using the sliders and letting mach set the number near to desired is better than entering the number in the box.

Stan
Title: Re: Relationship of Velocity/Accel to G0...
Post by: ger21 on June 25, 2010, 07:32:32 AM
Try the accel at 20
Title: Re: Relationship of Velocity/Accel to G0...
Post by: StanLewis on June 25, 2010, 05:41:19 PM
I will give it a whirl when I get the motors mounted on the real machine.  I have now taken the control panel apart a bit to start the next phase of the project.

Stan
Title: Re: Relationship of Velocity/Accel to G0...
Post by: StanLewis on June 26, 2010, 08:49:17 PM
Now that I have thought a bit more about the accel setting.....

This is missing the point....  The motors run VERY SMOOTHLY in the motor tuning dialog at 1000+IPM and accel at 100+ ips^2 but very roughly in the normal operation (esp. G0) of things....

I am trying to figure out why they would run smoothly under the motor tuning dialog and NOT SMOOTHLY elsewhere.  At this point the velocity and accel constants do not matter (not attach to a real machine....) except to give a context to the issue.  At this point, I could care less what the velocity/accel constants are.  BUT if I can only expect Mach to deliver 30% of performance in normal operations then I need to keep that in the back of my mind when I get to the real world.

This may be a good example of why I should consider a SmoothStepper and get off of the PP.

Stan
Title: Re: Relationship of Velocity/Accel to G0...
Post by: ger21 on June 26, 2010, 11:28:47 PM
You might want to try asking this on the Yahoo group. I may have seen an answer to this before, but don't remember. Art or Brian might have the answer.

On my PC, I get exactly the same performance in motor tuning and running g-code.
Title: Re: Relationship of Velocity/Accel to G0...
Post by: StanLewis on June 27, 2010, 09:02:15 AM
Cool, I will ask there as well...

Stan
Title: Re: Relationship of Velocity/Accel to G0...
Post by: RICH on June 27, 2010, 09:56:04 AM
Stan,
A SS will provide for an increase in the number of pulses that can be provided to the drives. The question is ....... are the drives and motors capable of using the pulses. The SS is generating the signal and not the PC/PP. The signal quality may be better at higher rates than from the pc and motor preformance will be improved.

The problem I am having is that you are trying to make a correlation of how a stepper motor will preform  running unloaded as to compared to one
loaded ( hooked to something ). That makes no sense at all from a practical point or theory. There is a world of difference. And depending on the application you should care about velocity and accel at this time. Well maybe not, since you already have the motor and you got what you got. You could use a motor sizing program and quickly see what the affects of varing  conditions provided you have known motor characteristics ( which you don't have ) and would see how velocity and acceleration comes into play at a given load.
Why do you think manufactures provide preformance motor curves?

Like Gerry, I get  the same performance in motor tuning and running g-code also.

Unloaded motor  you are mention IPM, yes relative is a sense only, since when a load is attached you will find that if your operating the stepper motor past some point of say max power the feedrate is no longer linear  because the torque is decreasing and as such the feedrate will no longer be linear
and any addition increase to the feedrate will be less than commanded. In fact you can almost generate a curve for your motor until it stalls based on the load!

RICH