Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: swarfboy on February 08, 2008, 10:40:00 AM
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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?
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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
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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?
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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
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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
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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
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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.
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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
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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
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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
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swarfboy,
your question is a bit of a "how bigs a hole" one. but I would say that you would be looking at 120 watt motors
running at 2-4000 rpm geared to give you a maximum of 3-4000 mm per minute a 250 cpr encoder would be about right
with a g320. and thats with a good pentium running up to 45khtz.
gecko's wont run brushless motors,you are looking at mega bucks for a brushless system.
remember you can fix encoders on to practicaly any dc pm motor to make a servo as long as they have a minimum of 12
poles they will run ok without cogging, I have modified a lot of "standard" motors successfully so I know it works.
In short you can build a servo system for really not much more than steppers.
I think you will struggle to build a brushless system without digging very deep into your pockets!
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I run servos on a Boxford lathe and the accel is 600 and velocity is 4850mm/min no loss of steps, the motors are nema 23 size.
0.22 Nm Stall Torque
1.7 Nm Peak Torque
3.1 Amps
They work on a 10 Amp linear 48 volt supply using 500 ppr encoders, the accuracy is .01mm/300mm all day long.
Graham.
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Graham,
What controller hardware and motors are you using? Sounds like what I'm looking for. Cost?
Brian
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here are some links
http://www.motioncontrolproducts.co.uk/index.php?cPath=27_29
http://www.motioncontrolproducts.co.uk/index.php?cPath=28_31
Graham.
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Hy Graham,
some little question about servo drivers from motioncontrol I read somewhere that I need to calibrate drivers to work with there servo motors and I don`t have oscilloscope did you have to do it your self? or it works straight from the box with no problem.
Do you need encoder on the motor or driver can work without them at all.
Thanks for giving info about motor size nema 23 there was very Little info about them.
Regards for Croatia.