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Motors are buzzing???Help
« 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

Offline RICH

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Re: Motors are buzzing???Help
« Reply #1 on: September 19, 2010, 10:53:02 PM »
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
« Last Edit: September 19, 2010, 10:54:48 PM by RICH »

Offline Hood

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Re: Motors are buzzing???Help
« Reply #2 on: September 20, 2010, 03:06:41 AM »
My guess by this statement is steppers
Quote
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
Re: Motors are buzzing???Help
« Reply #3 on: September 20, 2010, 04:25:01 AM »
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

Offline Hood

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Re: Motors are buzzing???Help
« Reply #4 on: September 20, 2010, 04:43:49 AM »

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

Offline RICH

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Re: Motors are buzzing???Help
« Reply #5 on: September 20, 2010, 06:32:31 AM »
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 

Offline Hood

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Re: Motors are buzzing???Help
« Reply #6 on: September 20, 2010, 06:52:15 AM »
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
Re: Motors are buzzing???Help
« Reply #7 on: September 21, 2010, 06:13:13 AM »
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

Offline RICH

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Re: Motors are buzzing???Help
« Reply #8 on: September 21, 2010, 06:46:27 AM »
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

Offline Hood

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Re: Motors are buzzing???Help
« Reply #9 on: September 21, 2010, 07:25:10 AM »
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