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  #1  
Old Mon 23 February 2009, 22:29
MariusL
Just call me: Marius #22
 
Centurion
South Africa
Loosing steps - noise interference problems

I opted for a 4:1 reduction on all motors.
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  #2  
Old Mon 02 March 2009, 12:02
MariusL
Just call me: Marius #22
 
Centurion
South Africa
. . . . loosing steps. I find with my machine being big (and heavy) it seems to be more prone to this loosing steps story. Has anyone played with higher current settings on the Geko drives?
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  #3  
Old Mon 02 March 2009, 12:17
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Marius, first get your motor accel. settings right before you wonder why you have lost stops. Your accel setting should be around 450 to 500 mm /s /s. With those 4:1 reductions you shouldn't need more torque.
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  #4  
Old Mon 02 March 2009, 13:22
MariusL
Just call me: Marius #22
 
Centurion
South Africa
Gerald,
My motor accel. is set to 500 mm/s/s. The pulse widths are set to 2us each. My Geko drives (201) current is set for somewhere between 3.5 to 4 amps.
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  #5  
Old Mon 02 March 2009, 19:37
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Your y-car is not any heavier that those of us who run spindles, so I don't see that your arrangement is much heavier - your big motors and belt reductions should be laughing at the load.

Under what conditions do you "loose steps"? Can you hear a noise when it happens?

To make any comments on the motor current, we need to know motor/drive types, motor wiring config, power supply voltage/capacitance etc.
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  #6  
Old Mon 02 March 2009, 22:50
MariusL
Just call me: Marius #22
 
Centurion
South Africa
Gerald,
It would seem to happen under acceleration (rapid move) and it makes buzzing noise when it happens.
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  #7  
Old Mon 02 March 2009, 23:44
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Does it happen on both X and Y axes?

The buzzing I am not familiar with. I know lost steps as a clatter noise. Maybe the difference is your belts softening the noise. I wonder if your PC is keeping up on the electrical side and that your noise is electrically induced?

Has it happened with normal cutting moves, or only with high-speed jogging moves? Could you try setting your max jog speed a bit slower?
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  #8  
Old Mon 02 March 2009, 23:45
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Are your motors getting anywhere near warm? Should be if your currents and voltages are correct.
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  #9  
Old Tue 03 March 2009, 14:01
Kobus_Joubert
Just call me: Kobus #6
 
Riversdale Western Cape
South Africa
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one more thing came to mind. Your setup with those big motors, big reduction gearbox and bigger motor mounting plate has more weight than my machine. As you are using the same springs that Gerald has on his drawings,could it not be a problem that the springs cannot hold the pinion against the rack when a change in direction occurs. Maybe give that spring a little more tention. Also make sure all the nuts / grubscrews are tight. Now I go to sleep again.
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  #10  
Old Tue 03 March 2009, 22:56
MariusL
Just call me: Marius #22
 
Centurion
South Africa
Gerald, what kind of tension should there bee on the spring?
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  #11  
Old Tue 03 March 2009, 23:01
gmessler
Just call me: Greg #15
 
Chicago IL
United States of America
Hi Marius,

I think this is what you're looking for.

Quote:
Originally Posted by Gerald D View Post
From the first post in this thread: "The springs for loading the motors should have a tension of about 12kg [25 lbs] while extended to about 128mm [5"] between the centers of the eyes at the ends of the springs. None of these specs need to be very exact."

Maybe someone else, with the same type of springs as you, could give you the dimension. What springs do you have?

It will also be influenced by the pinion diameter, thickness of d-sided tape, and height of the ground rail, but it isn't really that critical. The ballpark is 12kg [25 lbs] of tension.
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  #12  
Old Tue 03 March 2009, 23:20
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The quick answer is that there should be at least enough tension to stop the pinion from jumping out of the rack. (On this point I believe you have enough tension because the noise does not indicate your pinion is slipping when the fault occurs)

Then you need a bit more than the minimum (tooth jumping) to prevent the teeth from loosing contact inside the "groove" when taking a sudden hard cut. You can manually jerk the router and see if the motors want to move out of engagement.

Too much tension puts unnecessary load on the pinion shaft and bearings (I am a bit nervous of your long thin pinion shaft outside the bearing, but that is not related to the loosing steps issue in this thread)

In the original design I settled for 12kg spring tension, putting about 25kg pressure between the rack & pinion (due to the leverages involved), which I think was the limit allowed by Oriental Motor.
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  #13  
Old Tue 03 March 2009, 23:24
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Thanks Greg, my answer wasn't as quick as I had hoped and you slipped in while I was typing

Anyway, I think we can put the spring side to bed - that doesn't appear to be Marius's problem.
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  #14  
Old Wed 04 March 2009, 05:51
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
If you run the axes full length at different speeds, do you have the problem at all speeds?

Stepper motors resonate at certain speeds (shake and vibrate excessively). On non-CNC applications, those speeds are avoided. On a CNC machine, where an axis is expected to run at any speed required to synchronize with the other axes, resonance can be a problem.

The Gecko G201 has two options that might help. The trim-pot can be adjusted when the motor is moving very slowly (1/4 turn per second) . Adjust the trim-pot until the motor runs as smoothly as possible. There is also a Jumper option for use with large motors (frame size 42). I know that your motors are not that large, but some larger frame size 34 motors have many of the characteristics of the larger frame size 42 motors.

Some of my older PH299-03AA motors just didn't work well with the Gecko stepper drivers. (They were the older round motors with a 3/8-inch shaft.)

Also, did you install a 470uF capacitor directly across the power supply terminals on each G201 stepper driver? That capacitor is required if the stepper driver is more than one-foot (300mm) away from the motor. The G202 has that capacitor built in and the G203v does not require that capacitor.
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  #15  
Old Sun 15 March 2009, 05:34
MariusL
Just call me: Marius #22
 
Centurion
South Africa
Copied from another thread:

We call it the monster machine. It has impacted our production so much that even the folk working on the line has great respect for it. Something of a holy nature to them. We are doing our first big 3D mould in the week comming. probably about 36 hours of continues cutting.

I had to put the Pc and the driver electronics on a UPS and so solved all the noise interference problems. She runs solid now.
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