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Servo system
« on: February 08, 2008, 10:40:00 AM »
Been using Geckos with 10 microsteps and 0.9degree 250oz-in stepper motors on a 4 axis machine. I'm considering upgrading one of my machines to servos with rotary encoders.
I am aware that mach does not close the loop. Anyone have any recommendations for a servo system that works well with mach that closes the loop through the controller?
« Last Edit: February 08, 2008, 10:45:21 AM by swarfboy »
Re: Servo system
« Reply #1 on: February 08, 2008, 12:52:57 PM »
I'm building a servo system and using Gecko G320's. They are said to be the best as long as your power supply is below 80 volts (70 is best). Use these with 500 line encoders, most people say they have had good results.

If you can wait a bit Gecko are bringing out a new drive called the G380. They say it has overvoltage protection and motor short circuit protection and also raised the 128 count fault limit to something over 1000.

There's lots of other things different, I cant remember. Have a look on CNCZone in the Gecko forum for G380.

Cant wait to get mine going, still working on the mechanics though. I need 2 other drives so I'm in the queue for the new G380's.


Hope this helps
Re: Servo system
« Reply #2 on: February 08, 2008, 02:17:47 PM »
Unless its simple wiring I'm not one to attempt to assemble my own electronics. I see myself spending money and having a non working system.
I'd really rather buy a proven complete system, and just have to setup mach and mount th motors onto my mill. Any other recs?

Offline Hood

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Re: Servo system
« Reply #3 on: February 08, 2008, 02:23:24 PM »
I have heard good things about CNC Teknix drives, bit more expensive than Geckos but they have a few more features. Geckos also get a good name. The only servos drives I have used are Giidings and Lewis DSA drives (also can be  badged Allen Bradley DSD) They are more industrial type drives with lots of options and features but  probably a bit overkill  for smaller machines.
Hood
« Last Edit: February 09, 2008, 09:50:48 AM by Hood »

Offline comet

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Re: Servo system
« Reply #4 on: February 09, 2008, 09:37:30 AM »
Gecko 320 / 340 are as good as you can get. wiring is a doddle wire them common +5volt.
If you can wire a stepper system then there will be nothing here to worry you.
  I would say use 340's with encoders 500 counts (quad 2000) and you will be safe using 2x multiplier.
dont use 5x or 10x unless you are using them on a point to point system.
  Ie a drilling machine or pick and place.
Ive built a few systems using them and have never had a problem.
   Tony

Offline Hood

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Re: Servo system
« Reply #5 on: February 09, 2008, 09:49:45 AM »
Comet,
 I can assure you Geckos are not " as good as you can get" they are excellent for the money and will be all that most people  need, but there are a lot of other drives that have features way beyond what you get with Geckos, they also have a price way beyond Geckos as well ;) so if you dont need them its not worth it :)

Hood
« Last Edit: February 09, 2008, 09:51:51 AM by Hood »

Offline comet

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Re: Servo system
« Reply #6 on: February 09, 2008, 10:10:58 AM »
Hood,
  Perhaps I should have said "as good as needed for hobby aplication".Obviously there are
far better drives, I just think for the average user the simplicity of gecko's is hard to beat.

Offline Hood

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Re: Servo system
« Reply #7 on: February 09, 2008, 10:19:33 AM »
Yes, sorry Comet, I am just a grumpy old man LOL
I knew what you were meaning but just thought I should point out that there are other drives with much greater capabilities should these be needed, but as you said  most hobbyists wont need these features so  Geckos, Teknix etc are great.
Hood
Re: Servo system
« Reply #8 on: February 09, 2008, 03:29:06 PM »
Does anyone build offer a finished system using geckos? What sort of acceleration/velocity can you get with a servo system with small motors?
I currently get 275mm/sec^2 accell and 1000mm/min velocity without loosing step, using 10amp power supply, nema 23   0.9degree  250oz-in motors, using geckos with micro stepping. My the motors are directly coupled to the screw, I would like to do the same thing with the servos. I'm using preloaded 5 tpi 15mm ballscrews and linear guides. 
I think what I'm looking for are brushless servos with 1000 line rotary encoders and using quadrature.

Also I understand that you can home to and index mark on an encoder. I'm am interested in how this works, I think it would be more accurate than using homing switches.

Brian
« Last Edit: February 09, 2008, 03:34:02 PM by swarfboy »

Offline Hood

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Re: Servo system
« Reply #9 on: February 09, 2008, 03:52:36 PM »
You need a board for the Index homing. I use the one from Ed at www.cncbuildingblocks.com
 What happens is you press to home from Mach, the axis start moving and when the switch is hit the breakout looks for the Index pulse then tells Mach that the switch has been hit. Mach then reverses the axis and when the terminal count (set on breakout) is reached Mach is then told the switch has closed and that is the homing routine complete. The terminal count can be set quite high to accomodate for high count encoders which is handy on my system as I have 2000 line encoders (8000 as far as Mach is concerned).
 I use this on my lathe and it works very well.
Hood