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Author Topic: Encoders, steppers and mach  (Read 2816 times)

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Encoders, steppers and mach
« on: March 03, 2010, 08:46:44 AM »
Hi,

Im currently upgrading my gantry with an old esab bridge, this uses frction drive which im  a bit worried about but assured it will be fine, the servo system that would have been on this table would have had encoders turned by a gear rack on the rails, so if there was wheel slip i think it should have compensated for it?? So with my stepper system can i do this? am i right in saying mach would support encoders and would correct the position of the gantry according to the encoders rather than by the number of steps???

Not really on mach but the other question i have is about the steppers themselves, they are rated to take 90vdc, am i right in saying when you rectify an ac voltage it is reduced? Also can i over supply my steppers with voltage by a little and still not kill them? Im just wondering if i can rectify the 110vac in the shop and run the motors from it to save having a transformer?

Any help would be great

matt

Offline Jeff_Birt

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Re: Encoders, steppers and mach
« Reply #1 on: March 03, 2010, 09:34:12 AM »
Quote
so if there was wheel slip i think it should have compensated for it?? So with my stepper system can i do this? am i right in saying mach would support encoders and would correct the position of the gantry according to the encoders rather than by the number of steps???

No, mach cannot do this directly. You would need an external motion control board (kflop, Galil, etc) that can run steppers in a closed loop fashion.


Quote
Not really on mach but the other question i have is about the steppers themselves, they are rated to take 90vdc, am i right in saying when you rectify an ac voltage it is reduced? Also can i over supply my steppers with voltage by a little and still not kill them? Im just wondering if i can rectify the 110vac in the shop and run the motors from it to save having a transformer?


Two things:

1) The voltage rating on steppers indicated the constant DC voltage that can be applied to the coils to achieve the rated current. Generally steppers are driven with a voltage many times higher and the current is controlled to the rated amount. If your steppers really have a 90V rating you'll have a tough time finding a driver to handle even that voltage let alone anythign higher.

2) NEVER, I repeat NEVER, try to build a DC power supply without a transformer. The transformer not only can step the output voltage up/down it also provides isolation from the mains voltage. Without this isolation you libel to kill yourself (no kidding). Not trying to preach, just don't want to see you get hurt.
Happy machining , Jeff Birt
 
Re: Encoders, steppers and mach
« Reply #2 on: March 03, 2010, 02:14:55 PM »
Hi

I use Anaheim drivers, they are very powerful. Also when you rectify 110 you end up with about 180v dc
http://www.anaheimautomation.com/index.php

Good luck bud!!
Re: Encoders, steppers and mach
« Reply #3 on: March 03, 2010, 02:40:33 PM »
Thanks for the input,

I bought a g100 a while back with the aim of trying to do some of this stuff but have found it to be worthless, everytime i touched a home switch it would reset all axes to zero so ive given up on that. So what would anyone recommend?? I had a quick look at the kflop and galil but not knowing what i need i cat really judge them. I need to be able to drive 3 4.2A steppers, take encoder feedback from them and maybe drive some ordinary dc motors on the motorised z posts i have. Can any of these units do this? i think it would be easier to have a controller and separate drives since most of the integrated packages are only good for sort of 3.5A. What will it cost me??

Another question i have is how much should a decent 400w servo and gearhead cost me? Whats the difference between ac dc brushed and brushless?

Thanks again
Re: Encoders, steppers and mach
« Reply #4 on: March 04, 2010, 07:37:31 AM »
Although i'm a Mach3 user, I belive that EMC is fully closed loop with encoders although you will need to get your head round installing Linux to use it.