Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: ex apprentice on September 19, 2010, 08:44:16 PM
-
So Far so good,I have connected motors to drive boards, set mach ports and pins, mach is taking control of the motors everything seems OK until??
When I power up the control box for the boards the motors seem to be buzzing, if I go into motor tuning I can alter the speeds and velocities on all Axis
and if I press the up / down keys the motors spin as they should, forward or reverse even the slave axis is working
BUT
they seem very erratic and some times seem to stall or stop and just sit there sounding like they are spinning
They get rather warm so I have stopped playing and have spent time checking my settings etc all seem OK apart from the erratic running and stopping
The motors are not on the machine so no friction or binding they are just sat on the bench.
I have reset the motor drives back to full step rather than 1/4 step no change
Has anyone out there had this happen or can someone please guide me in the right direction
Soooo close yet so far away
-
Servos or steppers?
Post info on your driver and motors.
How are the motors wired?
Post your xml file
Sounds like you may have the amp setting to high for the motor if they are steppers , thus they will get warm and can behave strangely.
But rather than guessing give the above info for someones review.
RICH
-
My guess by this statement is steppers
they seem very erratic and some times seem to stall or stop and just sit there sounding like they are spinning
That is normal for a stepper when its overloaded and overloading can also mean setting acceleration or velocity beyond the capabilities of the motor and drive. Settings for steppers need to be done on the machine and is a case of trial and error to see what works. No harm in testing on the bench to get a feel for things but just dont spend too much time trying to fine tune things as it will all need done again when you fit to the machine.
As for temp, steppers do get hot and it is normal, most modern drives have current reduction when an axis is not moving but some dont. If a motor gets too hot to hold onto then you may want to look at current settings as Rich mentioned but if not then dont stress to much about it as its the nature of the beast.
Hood
-
Hi Rich & Hood
Thank you for your assistance
Rich; I am using steppers,I cant post xml as the system is on a stand alone PC with no connections outside of itself, the motors are wired in parallel - 8 wires
I do not have the info for the motors or driver boards (yet)
Hood; thank you for your calming words of advise.
As always when you do these things it was late and I just wanted to try things out, I will go back through the settings and check, check and check again
I didn't see any smoke?? so hopefully no damage has been done
I have reduced the current and speed (approx 100 rpm) all motors run at lower speed continuously in either direction without stopping
As soon as I increase the speed the problem of erratic stopping returns, its like the motors are loosing the signal to run
Will get onto the supplier today and discuss !!!!
thanks again
-
I have reduced the current and speed (approx 100 rpm) all motors run at lower speed continuously in either direction without stopping
As soon as I increase the speed the problem of erratic stopping returns, its like the motors are loosing the signal to run
Acceleration may be to high, its a juggling act with steppers to find the sweet spot. May also need a wider pulse, depends on make of drives and sometimes the computer but try setting Pulse Width and Dir prechange to 5.
Hood
-
I am using steppers.
I use Geco drives and what i did was provide, via dip switchs ( some have used a PP switching box ), such that they switch between using
Mach or DeskCNC as the controling software. Frankly, even though i did that it is never used and wasted my time.
Sounds like you have them working and Hood's reply applies.
Find the max velocity until they skip and lower it by 30%,then play with acceleration until they skip and lower it 30%. This is done with the motors installed on the machine since the motors will see a different loading when installed. Yes, you want speed but reliablity is more important.
Reliable operation at max power ( speed x torque ) so it's a comprimize and no two machines are alike.
Motor torque decreases as the speed increases. No value in having a fast machine and the stepper skips as soon as you cut sonething.
I suggest you go to the Geco site as it provides a lot of information on steppers.
RICH
-
I will add that often acceleration is more important than rapid speed, well that is if you cant have both like you can with servos ;)
On my Bridgeport I had 2500mm/min rapids but Accel was maxed at 40 if I remember. I dropped the Vel to 2200 and got the Accel up to 120 ( I think, been months since I have even had the Bridgeport powered up) and what a difference in machining times. Yes rapids are slower but the decrease in actual cutting time due to faster accel far outweighs that IMO.
Hood
-
Hello all
Thank you all for your advice and direction
I now have the motors running and seem OK, the only concern is the speed / rpm (or lack of it)
I can run the demo g codes and the motors appear to follow the commands
I have ignored the theory bit of setting the steps and entered values that made the motors spin (1000 steps / velocity 1000 acceleration 30
I also set the pulse & step width to 10 uS (I might need to refine that)
I did speak to the supplier and they are sending the specs, but I have found out I can set the boards to a power save mode that stops them buzzing when not moving
The speed thing is my next challenge, how to increase the rpm to approx 500 without losing steps or the motors stalling
Is the demo version of mach restricted in any way that might cause me problems with the above? (apart from the limit of 200 lines of code)
During the driver test I can achieve 75 K and the it tell me its stable and excellent (at the start i get the message pulsing to fast - but that then goes green +excellent)
what effect does this setting have on the system??
As I say in my profile all things mechanical are simple to me but this side of the project is new and the learning curve is steep.
But with all your help and and guidance I am sure I will start to understand whats what??
Thanks again
Peter
-
Peter,
You may skip the theory part but some understanding of it will help you achieve what your trying to achieve.
You need the steps per unit to be correct or the axis moves will not be correct. Sort of like having having big tires on a truck and it screws up the speedometer reading.
Your motors may not be able to run at 500 rpm when connected to the machine. Steppers run approx to 1000 rpm. Could be like using a grass cutter engine in a big truck. It dosen't have enough power to start moving the truck and stalls or the truck moves but should someone push back on the truck it comes to a stop.
Got to go but will try a different level of writing when responding.
RICH
-
I presume you are set up in metric units if so then it may be that the code you are running is set in imperial units. I am not sure what code you are running but sounds like it may be the roadrunner and I know it doesnt have a G20 in the code to define it as Imperial units, because of that your machine will think its metric so will run slow and small. What I mean is the code may ask for a 1 inch move at a feedrate of 2IPM , so your machine thinks that is a metric move so will move 1mm at a feedrate of 2mm/ min so it will take 30 seconds to move that 1mm.
Hood
-
Hi Rich
Thank you for your reply
Sorry i didn't mean it to sound that the theory part wasn't important, its just that I needed to get the system going for peace of mind
rather than a expensive pile of wire and bits for a paper weight.
I know that I will have to read lots more and do loads more research and that is only to be expected, I do want to understand how it all
comes together and what makes it tick
Although my goal is to build a machine to help my business, this part is like a hobby, I must start to spend less time enjoying playing and learning
and spend more time on the mundane work bit (customers!!!)
I have done the calcs for the steps through the gearing and final drive but will go back to that now I know the system does operate
The target is to achieve approx 400" / min travel for the X & y axis according to my numbers below
From 500 rpm on the motor, bearing in mind I will have a 2:1 reduction in rpm onto
the drive gear so that will give me 250 rpm at the out put
The Drive gears have a PCD of 26mm which calculates to 81.68mm per revolution (or two revs of the stepper)
(400 inches a minute = 10,160mm/min)
10,160 mm/min = 124.387 rpm at the output gear = 250 rpm at the stepper
On top of that rpm will be rapid feed for positioning hence it would be nice to get nearer the 500 rpm (without losing steps)
I hope this makes some sort of sense??
Hood
I have just read your reply, spot on I will have to look at the config, does sound hopeful though (Clutching at Straws)
I will let you know what I find out
Peter
-
Just a word of warning, you need to keep to one set of units for your setup, ie if under the Config menu you have the default units set to Metric you need to calculate your steps per unit as metric and vice versa.
That does not mean you can not use Imperial code, all you need to do is tell Mach that it is imperial by having a G20 at the start of the code, if its metric code it would be a G21.
Hood
-
BTW what drives do you have?
Hood
-
Hi Hood
sorry but what does the BTW stand for?? I am sure I will feel even dumber when you reply!!
Peter
-
By The Way :)
Hood
-
BTW
I did say I would feel dumber!! :-[
Peter
-
;D
No need to feel dumb, I would say you were dumb if you hadnt asked, its the way to learn, whether its internet abbreviations or Mach setup.
Questions are always good :)
Hood
-
Hi all, again
Can someone explain what below means and does, trying to learn mach speak??
During the driver test I can achieve 75 K and the system tells me its stable and excellent
(at the start i get the message pulsing to fast - but that then goes green +excellent)
what effect does this setting have on the mach control and motor control systems??
Peter
-
The kernel is what Mach can pulse at, so for example if you had it set at 25KHz that would be a max of 25,000pulses per second that Mach could output for an axis.
If for example you have 1000 steps per mm then that would mean you Max velocity that is possible at 25KHz would be 25000/1000 = 25mm per second or 1500mm per min. So if you were wanting faster than that and of course if your motors were capable of faster, then you would need to increase the kernel to suit.
With your steps per unit and the probable max speed then I think 25KHz would be fine and using higher would not help and may actually hinder as it would possibly use more of your computers processing power.
Hood
-
Hi all
Following on from Hood's explanation of mach reading road runner as it comes (no G20 to tell mach its English / imperial)
How do I load the sample roadrunner G code and then edit it to put the G20 code at the beginning to tell mach its in English / imperial?
simple question I know and it is probably written or on a video somewhere
Peter
-
Load the code then once open in Mach click the Edit button, it should open in notepad and yo can then type in G20 on the first line of the code. Close it and it will ask if you want t save, say OK and then thats it.
Hood
-
Hi Hood
Did try the edit button, the load screen (Please wait generating path)flashes and then nothing, no notepad, maybe its because i have the demo version?
Peter
-
Do you have the code opened in Mach first before pressing edit?
If so then go to Config menu then General Config and you will see at the top in the middle section the editor address, choose browse and go to C:\Windows\ and choose notepad.exe
Hood
-
Hood
Your a star, thank you.
Worked a treat, just got to sort out with the supplier the motor speed limitations
and then buy the license for mach
Hopefully this is the start
I can then look at doing some drawings etc and converting to code to run through mach
Then start the table build (easy'ish bit)
Peter
-
Sorry
not yet the start, still have to work out the limits, homes, soft limits, Z axis (floating)THC, etc etc etc so will be a few more posts I think and a lot more questions for definite
thank you for everything so far
Peter
-
No probs :)
Hood