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  #1   Report Post  
oparr
 
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Default Gecko G320 and 12V servo motor

Anybody using a G320 drive with a 12V servo motor? How risky is this? G320
specs state 18V as minimum voltage and voltage should not exceed motor rated
voltage by more than 5V. Would forward/reversed biased diodes in parallel
connected in series with each armature lead be wise or not necessary? I'm
about to call Gecko but the more help the better.


  #2   Report Post  
william_b_noble
 
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I wouldn't worrry about it - set a current limit to not exceed the motor's
max current and you'll be OK. voltage doesn't really matter to a DC motor
unless you exceed the insulation breakdown voltage, it's the current that
matters. When run from a battery or a uncontrolled source, voltage and
current and RPM are all related, but with a servo drive, you can set the
current limit which will control the voltage appropriately. I wouldn't want
to put much over 100VDC on a 12V motor, but I woldn't worry about 20 or
30VDC
bill

"oparr" wrote in message
news:UaDyd.5958$113.5247@trndny03...
Anybody using a G320 drive with a 12V servo motor? How risky is this? G320
specs state 18V as minimum voltage and voltage should not exceed motor

rated
voltage by more than 5V. Would forward/reversed biased diodes in parallel
connected in series with each armature lead be wise or not necessary? I'm
about to call Gecko but the more help the better.




  #3   Report Post  
Tom Gardner
 
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No help from me but, I would like to know more about what you are doing. I
am also working on a CNC project and am trying to absorb as much as
possible. I haven't bought drives yet but am leaning heavily to Rutex. I
did find a good source for motors and got three and a Compumotor 6K4
controller.


"oparr" wrote in message
news:UaDyd.5958$113.5247@trndny03...
Anybody using a G320 drive with a 12V servo motor? How risky is this? G320
specs state 18V as minimum voltage and voltage should not exceed motor
rated voltage by more than 5V. Would forward/reversed biased diodes in
parallel connected in series with each armature lead be wise or not
necessary? I'm about to call Gecko but the more help the better.



  #4   Report Post  
Fred R
 
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Post your question on the Yahoo Groups geckodrive group and Mariss will
answer it himself, typically immediately. Great guy. (Happy customer.)

--
Fred R
________________
Drop TROU to email.
  #5   Report Post  
oparr
 
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Thanks Bill.

"william_b_noble" wrote in message
news:1103823293.2583dff7c038f4d3af049c4f851e0f36@t eranews...
I wouldn't worrry about it - set a current limit to not exceed the motor's
max current and you'll be OK. voltage doesn't really matter to a DC motor
unless you exceed the insulation breakdown voltage, it's the current that
matters. When run from a battery or a uncontrolled source, voltage and
current and RPM are all related, but with a servo drive, you can set the
current limit which will control the voltage appropriately. I wouldn't
want
to put much over 100VDC on a 12V motor, but I woldn't worry about 20 or
30VDC
bill

"oparr" wrote in message
news:UaDyd.5958$113.5247@trndny03...
Anybody using a G320 drive with a 12V servo motor? How risky is this?
G320
specs state 18V as minimum voltage and voltage should not exceed motor

rated
voltage by more than 5V. Would forward/reversed biased diodes in parallel
connected in series with each armature lead be wise or not necessary? I'm
about to call Gecko but the more help the better.








  #6   Report Post  
oparr
 
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Thanks, I posted there but looks like he's sick today.

"Fred R" "spam wrote in message
...
Post your question on the Yahoo Groups geckodrive group and Mariss will
answer it himself, typically immediately. Great guy. (Happy customer.)

--
Fred R
________________
Drop TROU to email.



  #7   Report Post  
Richard J Kinch
 
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oparr writes:

Anybody using a G320 drive with a 12V servo motor? How risky is this?
G320 specs state 18V as minimum voltage and voltage should not exceed
motor rated voltage by more than 5V. Would forward/reversed biased
diodes in parallel connected in series with each armature lead be wise
or not necessary?


It's likely the motor can handle 18 VDC.

Note that DC motor voltage is related to speed. You can also limit the DC
voltage to the motor by limiting the RPMs in software.
  #8   Report Post  
oparr
 
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It's likely the motor can handle 18 VDC.

I have two 27V 5.6A power supplies from a previous project so 24V servos
would have been ideal but unfortunately not possible, have to use 12V
servos. The current at 12V, rated RPM and maximum torque is 2.3A. I'm going
to test the performance of the motors with the 27V PS under real mechanical
load using a 6 ohm 40W series resistor.

"Richard J Kinch" wrote in message
.. .
oparr writes:

Anybody using a G320 drive with a 12V servo motor? How risky is this?
G320 specs state 18V as minimum voltage and voltage should not exceed
motor rated voltage by more than 5V. Would forward/reversed biased
diodes in parallel connected in series with each armature lead be wise
or not necessary?


It's likely the motor can handle 18 VDC.

Note that DC motor voltage is related to speed. You can also limit the DC
voltage to the motor by limiting the RPMs in software.



  #9   Report Post  
Richard J Kinch
 
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oparr writes:

The current at 12V, rated RPM and maximum torque is 2.3A.


Dunno what you application is, but that is a puny motor.
  #10   Report Post  
oparr
 
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More than sufficient for the application. With the PS adjusted to 23V and
with a 8 ohm series resistor the voltage fluctuates between 13 and 16V at
the motor indicating a maximum current draw of just over 1A. And this
included loading the table with a 25lb weight (about 25 times what I'll be
using), stopping and starting etc..

"Richard J Kinch" wrote in message
. ..
oparr writes:

The current at 12V, rated RPM and maximum torque is 2.3A.


Dunno what you application is, but that is a puny motor.





  #11   Report Post  
william_b_noble
 
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Oparr - I'd strongly suggest making a test without the resistor - take the
same measurments - if you are comfortable that the motor is not
overstressed, use it without the resitor (you can add a fuse if you like) -
in a servo circuit, the series resistor degrades performance and accuracy,
you will be better off without it.

as an aside to those using low voltage motors, the big pile of Minarik
controllers I picked up has a bunch of low voltage DC motor controllers - in
the 12 to 48 V range - I haven't tested any yet, It will be a few days
before I have access to them again, but if you have interest in the Minarik
controllers, drop me a note. The DC controllers I have tested are all for
90 to 180VDC motors (with 110 to 220VAC input).


"oparr" wrote in message
news:5Qfzd.8273$113.6842@trndny03...
More than sufficient for the application. With the PS adjusted to 23V and
with a 8 ohm series resistor the voltage fluctuates between 13 and 16V at
the motor indicating a maximum current draw of just over 1A. And this
included loading the table with a 25lb weight (about 25 times what I'll be
using), stopping and starting etc..

"Richard J Kinch" wrote in message
. ..
oparr writes:

The current at 12V, rated RPM and maximum torque is 2.3A.


Dunno what you application is, but that is a puny motor.





  #13   Report Post  
oparr
 
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Motor spins way to fast. Bearings and brushes will go in no time. Still
looking for a lower voltage drive. The popular MC33886 H-bridge controller
operates from 5 - 30V and all other support chips (quadrature to count,
counters etc.) can be found in 5V versions so don't see why such a drive
doesn't exist. May have to make my own.

Called Gecko on Friday for their take on my scenario but their Tech Support
was out sick. Also, left e-mail in the Gecko Yahoo group but it hasn't
appeared yet.

"william_b_noble" wrote in message
news:1103997627.649303010185c3683aa0ff5057d00f34@t eranews...
Oparr - I'd strongly suggest making a test without the resistor - take the
same measurments - if you are comfortable that the motor is not
overstressed, use it without the resitor (you can add a fuse if you
like) -
in a servo circuit, the series resistor degrades performance and accuracy,
you will be better off without it.

as an aside to those using low voltage motors, the big pile of Minarik
controllers I picked up has a bunch of low voltage DC motor controllers -
in
the 12 to 48 V range - I haven't tested any yet, It will be a few days
before I have access to them again, but if you have interest in the
Minarik
controllers, drop me a note. The DC controllers I have tested are all for
90 to 180VDC motors (with 110 to 220VAC input).


"oparr" wrote in message
news:5Qfzd.8273$113.6842@trndny03...
More than sufficient for the application. With the PS adjusted to 23V and
with a 8 ohm series resistor the voltage fluctuates between 13 and 16V at
the motor indicating a maximum current draw of just over 1A. And this
included loading the table with a 25lb weight (about 25 times what I'll
be
using), stopping and starting etc..

"Richard J Kinch" wrote in message
. ..
oparr writes:

The current at 12V, rated RPM and maximum torque is 2.3A.

Dunno what you application is, but that is a puny motor.







  #14   Report Post  
oparr
 
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The resistor is reducing the voltage and hence the speed of the motor,
preventing a 5000 RPM motor from spinning at over 10000 RPM leading to
bearing, commutation, brush and possible winding (excess centrifugal force)
problems. Yes, I can run the motor at 24V and 50% duty cycle and do the same
thing but there may be other issues.

Using 10 rectifier diodes in series I see only a .8V variation at the motor
(13.6V - 14.4V) with the PS at 23V and under the same load conditions
mentioned earlier. Yes, I'll need 20 for both directions but they're cheap.
Bottom line....G320 and 12V motor should be feasible one way or another at
24V. Just waiting on Gecko's take on it and still looking for a 12V
compatible drive.

"Ned Simmons" wrote in message
...
In article 5Qfzd.8273$113.6842@trndny03, says...
More than sufficient for the application. With the PS adjusted to 23V and
with a 8 ohm series resistor the voltage fluctuates between 13 and 16V at
the motor indicating a maximum current draw of just over 1A. And this
included loading the table with a 25lb weight (about 25 times what I'll
be
using), stopping and starting etc..


The resistor isn't doing anything useful and may actually degrade the
performance of the system. As suggested earlier, you'd do better to
limit the motor's speed in software.

Ned Simmons



  #15   Report Post  
Russ Wizinsky
 
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If they are like stepper motors, your supposed to run the motor at 5 to 20
times the rated voltage. I've not messed with servos, I'm considering it
because I've got a machine I want to retro fit controls on and I'd have to
replace all the servos, but I'm just not into "Tuning" the servos.


"oparr" wrote in message
news:UaDyd.5958$113.5247@trndny03...
Anybody using a G320 drive with a 12V servo motor? How risky is this? G320
specs state 18V as minimum voltage and voltage should not exceed motor
rated voltage by more than 5V. Would forward/reversed biased diodes in
parallel connected in series with each armature lead be wise or not
necessary? I'm about to call Gecko but the more help the better.





  #17   Report Post  
oparr
 
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Default

This is guaranteed to play havoc with the servo tuning.

I'll discover this for myself first hand then.

I still don't understand why you can't simply limit
the motor velocity in your software.


Me neither, it's just not going to be the first option tried. Prefer a
hardware solution.

AMC makes some that will operate as low as 16V


Thanks!

"Ned Simmons" wrote in message
...
In article 2Alzd.14978$rL3.7321@trnddc03, says...
The resistor is reducing the voltage and hence the speed of the motor,
preventing a 5000 RPM motor from spinning at over 10000 RPM leading to
bearing, commutation, brush and possible winding (excess centrifugal
force)
problems. Yes, I can run the motor at 24V and 50% duty cycle and do the
same
thing but there may be other issues.

Using 10 rectifier diodes in series I see only a .8V variation at the
motor
(13.6V - 14.4V) with the PS at 23V and under the same load conditions
mentioned earlier. Yes, I'll need 20 for both directions but they're
cheap.
Bottom line....G320 and 12V motor should be feasible one way or another
at
24V. Just waiting on Gecko's take on it and still looking for a 12V
compatible drive.


The resistor is a bad idea, but the diodes are a *really bad* idea. At
least the resistor is a linear circuit element. The diodes are going to
introduce a stepped voltage drop between the amp and motor. This is
guaranteed to play havoc with the servo tuning.

I still don't understand why you can't simply limit the motor velocity
in your software. The amp is isn't going to deliver any more voltage
than what is required to drive the motor at a given speed.

Re low voltage amps, AMC makes some that will operate as low as 16V, but
I don't recall if they're for brush or brushless motors, and I'm sure
they'll be much more expensive than the Gecko drives.

Ned Simmons



  #18   Report Post  
HaroldA102
 
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i always look for faster and faster
  #19   Report Post  
Fred Smith
 
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On Sat, 25 Dec 2004 20:15:34 GMT, "oparr" wrote:

Motor spins way to fast. Bearings and brushes will go in no time. Still
looking for a lower voltage drive. The popular MC33886 H-bridge controller
operates from 5 - 30V and all other support chips (quadrature to count,
counters etc.) can be found in 5V versions so don't see why such a drive
doesn't exist. May have to make my own.


http://www.imsrv.com/deskcnc/servospecs.pdf

These drives operate at 12-30volts. $65/ea in quantities of 3 or
more.

Fred Smith - IMService
http://www.cadcamcadcam.com/hobby
  #20   Report Post  
oparr
 
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Thanks Fred. Seems to be exactly what I'm looking for.

"Fred Smith" wrote in message
...
On Sat, 25 Dec 2004 20:15:34 GMT, "oparr" wrote:

Motor spins way to fast. Bearings and brushes will go in no time. Still
looking for a lower voltage drive. The popular MC33886 H-bridge controller
operates from 5 - 30V and all other support chips (quadrature to count,
counters etc.) can be found in 5V versions so don't see why such a drive
doesn't exist. May have to make my own.


http://www.imsrv.com/deskcnc/servospecs.pdf

These drives operate at 12-30volts. $65/ea in quantities of 3 or
more.

Fred Smith - IMService
http://www.cadcamcadcam.com/hobby



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