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  #1  
Old Wed 31 December 2008, 05:04
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Gecko / Motor Tuning

Recently when I tried tuning the Gecko drives with the motors, there didn't seem to be much difference in the performance of the drives as we moved the pot on the Gecko.

I sent a note to Gecko and Marcus sent me the following informtion that might be useful to others.

"For adjusting the drives we recommend you set the motors to about 1RPS (60RPM) as that will create the most noticeable difference in settings. If you are running at higher speeds the changes will be negligible and will go unnoticed."

With this information, I will look at the motors again though I believe they are running very smoothly.

Hope this helps.
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  #2  
Old Wed 31 December 2008, 05:15
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The 60 rpm is the motor speed . . . . before the gearbox. If you have a 7.2 gearbox attached, and a 1.5" diameter pinion, you are talking around 40 inches per minute.

Easiest way to feel the vibration is to hold one hand on the motor while tuning with the other hand.
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  #3  
Old Wed 31 December 2008, 06:26
J.R. Hatcher
Just call me: J.R. #4
 
Wilmington, North Carolina
United States of America
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On a gecko 203V you can see the adjustment screw. Is this adjusting so exact that you could set one, then match that screw position on all others, if all motors were the same???
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  #4  
Old Wed 31 December 2008, 08:18
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I found that the screw position is the same.

Some might think that the tuning is not important because the cutting speeds are generally much higher than 40 ipm . . . . . . .

Not true! If you cut out a circle, a motor's speed varies sinusoidaly from zero, to max, to zero, to min, to zero. At 4 points along that circle's circumference, that motor WILL be turning at the resonance speed. If you examine a circle cut on a MM , particularly with a direct drive motor, you can clearly see the points where the cut is a bit rough. A bad one is when the resonance speeds are at the 45 degree points (NE. NW, SE, SW compass points). That means the X and Y motors are resonating at the same point on the circle, making the cut quality worse than twice as bad - the motors get each other "shaking". And if you have a flimsy gantry that resonates at the same point as the motors, you get a violent reaction. (early SB's)
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  #5  
Old Mon 05 April 2010, 12:37
Kobus_Joubert
Just call me: Kobus #6
 
Riversdale Western Cape
South Africa
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I hope I am posting in the correct place.
I noticed something this weekend.
I was worried that my motors was running a little bit on the HOT side and decided to drop my current limiting resistor to limit the current.
Well, from my experience it did not change much. The steppers still run nice and hot, but now I notice that I can move the gantry while the steppers are energised.
On my 5 - 6 Amp setting everything was solid as a rock. Now at 4 Amp I can push and pull and I move the steppers...
Is this what one would expect ?
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  #6  
Old Mon 05 April 2010, 17:41
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Reducing the current reduces the holding torque of the motor, so you may be able to move the axis by hand if you lower the current drawn by the motors.

I prefer to lower the voltage to reduce heat. Reducing the voltage mostly affects the top speed of the motors. In a CNC router application, we rarely use the top speed. Going from 1,500 RPM down as low as 750 RPM makes little real difference because, even at 750 RPM, with a 7.2:1 gearbox and a 1.5-inch diameter spur gear, the axis will move at 490 inches per minute. Eight inches per second, even while jogging is pretty good.

Amps X Voltage = Watts; so, to lower the wattage, you can either lower the current (Amps) or you can lower the voltage.
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  #7  
Old Mon 05 April 2010, 23:56
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Kobus, I would be curious to hear what the actual (measured) temperature of your motors were when you decided they were a little too hot. Also, did the major heating occur while standing idle, or while cutting a long file?

Your ability to move the gantry by hand relates to:
- using non-geared drives (motor with pinion gear direct on its shaft)
- the type of drives you use and the extent to which they go into "current-limit" mode when the axis has been idle for a second or so.

If you drop the current by 10%, the torque should also drop by 10%.
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  #8  
Old Tue 06 April 2010, 05:44
Kobus_Joubert
Just call me: Kobus #6
 
Riversdale Western Cape
South Africa
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I never measured the temperature, just had my hand on it.
They get hot when working like a long 3D cut where they move in all directions ALL the time.
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  #9  
Old Tue 06 April 2010, 07:42
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
How long do you think you can hold your hand without saying EINA!? If it is 3-4 seconds, the temp is not too bad.
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  #10  
Old Tue 06 April 2010, 12:13
Kobus_Joubert
Just call me: Kobus #6
 
Riversdale Western Cape
South Africa
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Ja longer than 4 seconds...but I am tough...or dumb..
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