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Offline comet

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A couple of questions re servo's
« on: December 28, 2011, 11:06:02 AM »
Hi and Merry Christmas/happy new year!
firstly I'm doing a bf20 conversion using gecko 320x drives. my x an y are 24 volt and my z is 36 volt.
I have a 36v powersupply and I'm thinking as long as i don't try and run the 24volt servos past there rated rpm at 24 volt I should be OK powering them from the 36 volt power supply?
  Also fat32 or ntfs whats the best for mach? I know audio recording software works better with fat32 because it writes in realtime rather than blocks ala NTFS,would this be an advantage ?
Finally (for now) how have you guys got around the limeted space on the y axis when fitting ballscrews?
   regards
 Tony
Re: A couple of questions re servo's
« Reply #1 on: December 28, 2011, 02:16:37 PM »
No, I would guess that's probably not a smart thing to do.  The Gecko uses PWM, which means it is switching the full supply voltage on and off to control the RMS (average) current.  Running the Geckos at above rated voltage for the motors would not only leave open the possibility of cooking the motors if the Gecko fails, andI would think it would also be likely to result in the motors running hotter than they would if run within their ratings.  If you want to get a definitive answer, I would contact Gecko tech support directly.

Regards,
Ray L.
Regards,
Ray L.

Offline comet

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Re: A couple of questions re servo's
« Reply #2 on: December 28, 2011, 02:40:20 PM »
well my thinking is that rpm and volta\ge are linked and ive checked this ie at 2800 rpm on a gecko the motor is drawing 24 volt
Re: A couple of questions re servo's
« Reply #3 on: December 28, 2011, 03:44:57 PM »
well my thinking is that rpm and volta\ge are linked and ive checked this ie at 2800 rpm on a gecko the motor is drawing 24 volt

The motor does not "draw" voltage.  Voltage is applied by the driver, at the power supply voltage, and that voltage induces current in the motor windings.  Most motor ratings are determined by thermal limitations.  What you measure with a voltmeter is an average value, but with a PWM drive, like a Gecko, it is the instantaneous values, which CANNOT be measured with a simple meter, that will get you into trouble.

Regards,
Ray L.
Regards,
Ray L.

Offline comet

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Re: A couple of questions re servo's
« Reply #4 on: December 28, 2011, 06:42:42 PM »
OK, so ,whats the best way of knocking down my 36v to 24V and still deliver 2 x 6amps @24v ? would a couple of 317 voltage regulators (3amps each) wired in parallel per motor do it?
Re: A couple of questions re servo's
« Reply #5 on: December 28, 2011, 09:07:32 PM »
Wiring 3-terminal regulators in parallel is not wise.  One will invariably be set to a slightly different voltage than the other, and end up doing most of the work.  The right way to do it is to build a high-current regulator using a pass transistor capable of handling the full load current.  An analog regulator will also be very inefficient, since 1/3 of the energy will be lost as heat in the regulator - you'll need some hefty heat sinks.  You'd really be FAR better off just getting a 24V supply.  Do you NEED the full 36V for the Z axis?  If youi don't need it to go to full rated RPM, run all the motors on 24V.  The only thing you'll lose is top-end speed on the Z axis will be reduced by 33%.

Regards,
Ray L.
Regards,
Ray L.

Offline comet

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Re: A couple of questions re servo's
« Reply #6 on: December 29, 2011, 03:44:02 AM »
its ok I have an 18v toroid to make a 24 vold supply just a bit tight for space,can you "stack" toroids phisically not electrically,because i know they can do weird stuff!
Any thoughts on FAT32 vs NTFS ?

    Tony
Re: A couple of questions re servo's
« Reply #7 on: December 29, 2011, 09:34:50 AM »
I don't think you'd want to stack the toroids without some space (perhaps an inch?) between them.  Either file system should be fine.

Regards,
Ray L.
Regards,
Ray L.
Re: A couple of questions re servo's
« Reply #8 on: January 30, 2013, 09:53:36 AM »
OK  it may be to late but voltage isn't what burns its amps. Normally higher voltage will induce higher amps into the same load which would cause overheating.
The Gecko 320x has current you can set. The 36 volts at rated amps will work fine you will have higher rpm then rated so be careful of this. The hard part will be setting the Gecko current output with the little pot adjustment isn't real accurate. The 320x is rated at 20 amps at full turn so it would be approxamately 5 amps per 1/4 turn.
A DC amp meter in line could be used to set it exactly if you want to get a  safe max setting.
The PWM out put of the Gecko won't heat the motor as much as straight current would, this is why a switching power supply doesn't use large transformers the on off state of PWM reduces heat drasticly.
I have this ultimate set of tools I can fix it.

Offline Bloy

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Re: A couple of questions re servo's
« Reply #9 on: February 01, 2013, 09:53:10 PM »
I'm in agreement with Machinehead57.
My router uses four motors, two matched and sharing/slaving the y axis/b axis, and the other two on z and x.   the Y motors are 75VDC, and the x and z are 56VDC. Initially I too was nervous about running at the same voltage and rewired the toroid to output the two votages(after rectification).  But then the "one fault all fault" didn't work.  I was informed as Machinehead57 notes that all the motors can run off the 75VDC .  I believe it was Dan Mauch who told me this.
It is very unlikely I will ever bee running all the motors full out causing the motors to burn up.   HOWEVER, there will be a slight increase in the brush wear... but I haven't had any problems so far.    

It IS neat to see the smaller motors zip about if I decide to run the shared 75VDC yaxis motors at their max... ;D

I remember testing it on the "roadrunner" .    Although I built the machine strongly, It really shot through the program with gusto causing a little nervousness.  But didn't notice much heat in the smaller motors.   In real use, the smaller voltage motors work just fine.
« Last Edit: February 01, 2013, 10:12:10 PM by Bloy »