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View Full Version : Help Understanding Servos, Encoder and Motion Controllers



freak_brain
10-17-2008, 10:21 AM
Hello Friends,

I am starting on my second machine. My first was a stepper motor machine. I am now wanting to servo a machine. I ran into some Galil products pretty cheap but I'm not sure if I can use them on these hobby type machines. I have a Galil DMC-730 motion controller, and 3 Galil 900ozin servos but I'm not really sure how it all works together. Sooooooo for starters any help with the following questions would be much appreciated.

Can the Galil DMC-730 work with a regular PC with Mach3 on it?

Can I use the 10 wire encoders with Gecko drives if I don't use the other Galil stuff?

And last, what other type of electronics would I need? I assume some type of power supply and maybe more???

Maybe I would be better off to off the motion control and buy geckos???? I looked on Galil's website and found no information about the products I have so I am guessing they are out dated. Thanks for all your help!!!

Allen

TOTALLYRC
10-17-2008, 01:17 PM
Hello Friends,

I am starting on my second machine. My first was a stepper motor machine. I am now wanting to servo a machine. I ran into some Galil products pretty cheap but I'm not sure if I can use them on these hobby type machines. I have a Galil DMC-730 motion controller, and 3 Galil 900ozin servos but I'm not really sure how it all works together. Sooooooo for starters any help with the following questions would be much appreciated.

Can the Galil DMC-730 work with a regular PC with Mach3 on it?

Can I use the 10 wire encoders with Gecko drives if I don't use the other Galil stuff?

And last, what other type of electronics would I need? I assume some type of power supply and maybe more???

Maybe I would be better off to off the motion control and buy geckos???? I looked on Galil's website and found no information about the products I have so I am guessing they are out dated. Thanks for all your help!!!

Allen

According to the Mach3 website the Galil plugin only works with pci slot devices or ethernet port devices. That one looks to be serial port.

If the ten wire servo's are diferential encoders and you can figure out which wire goes to what, its possible. It would require a differential to single ended chip just before the gecko or just use a and b off the encoder or put new encoders on the motors. It is all up to you and how much you can do for yourself. Power supply to match the servo motors. Remember Gecko's are good to an absolute max of 80v. If those motors are say,120vdc, they will run slower on 80v. If the Galil is a serial board, sell it and then use the money for Gecko's or something similar.

Al_The_Man
10-17-2008, 03:53 PM
The DMC-700 series is an older legacy unit and meant to run as a stand-alone system, It either came with analogue output or built in servo amplifiers.
It is quite a powerful unit, but a bit dated now.
Although you could run it with native commands over a serial bus, the main object was to run stand alone applications with a downloaded program into memory.
If this unit does not have the built in amps, you would need analogue type drives with built in or separate P.S. or for the motors you have.
Unfortunately, there is hardly anything in the way of an off-the-shelf PC HMI to run this unit.
Al.

freak_brain
10-18-2008, 12:02 AM
Thanks to both of you. You have made my decision easy for me. I think it's in my best interest to sell the motion controller, if I can, and keep the motors. The motors, like the the motion controller are dated but with new encoders will be just fine. Galil did send me the specs, in .pdf format, on the motors and encoders. However, the wiring for the encoders didn't match what I have. As for the motors they are new, nema34 80VDC motors... so can I use them with geckos?

If I can use the motors I could throw away the other stuff and still not get hurt. I only gave $75 bucks for everything, 4 motors and the DMC730. Not that I will throw it away but you get what I am saying!!

So...one last question. What do I need to look for when buying the encoders?

Thanks again to both of you!!!
Allen

Al_The_Man
10-18-2008, 12:29 AM
I am just wondering how you get 10 wire encoders? Is there any information on them?
Do you know the resolution?
I assume they are DC servo's, as I believe that is all Galil sold.
If you are replacing encoders and they are through-shaft type, you need to get for the same dia shaft. Renco have NOS encoders on ebay right now for $20.00, most are 1/4" shaft single ended.
Al.

freak_brain
10-18-2008, 12:47 AM
I wonder how you know more about what I have than I do Al.... Are you my neighbor and looking in my window?? lol.... I was mistaken when I said I have 10 wire encoders. actually I do but they are on the nema23 servos I have that have BEI encoders. The encoders on the Galil motors are 8 wire Renco's. I emailed Renco and asked them about them. Here is what they told me..

The part number 77678-126 is not longer active.

I have found RM21D-1000-3/8-G6-5-CA36-LD.

( I do not know the gating option on this encoder.)

I am trying to get further information in our old files.

If I find any more info I will let you know.

This unit was built for Galil Motion Control and they may be able to give you more information


I wish I knew how to put that PDF file on here.

6 of the 8 wires match Galils book. With 2 wires not matching it makes me think that the wiring they have in the book is for another encoder.

They have 3/8" shaft on the motor and it goes thru the encoder.

Maybe I should just get new ones!! What do you think Al?

Thanks

freak_brain
10-18-2008, 12:52 AM
Oh, I forgot. They are 1000 point resolution

Al_The_Man
10-18-2008, 01:09 AM
I am sure you looked at the spec sheet?
http://wwwpdb.renco.com/ansicht/Renco/media/img/647095.pdf
Yes they look like 1000p/rev 3/8" dia shaft with 5v Line Driver output.
If Gecko accept the resolution you will get, then you should be able to use them.
At the very least they should produce A,B and Marker pulse.
If Gecko only accept single ended, then forget about the /A,/B,/Z pulses.
I have never used Gecko products, so I can't help there.
The final resolution will be 1k x4 /rev = 4000 counts.
If the PDF file is within size, you can upload it by going to the advanced options when posting.
Al.

freak_brain
10-18-2008, 01:27 AM
Al,

Thank you very much!! A lot of this I don't understand but I am learning thanks to people like you.

I didn't look at that pdf until you posted a link... I just forgot to go back to their website.

Anyhow, Thanks again for your help. Now maybe the gecko people can help me on the resolution restriction of their products.

Allen

TOTALLYRC
10-18-2008, 03:51 AM
Al,

Thank you very much!! A lot of this I don't understand but I am learning thanks to people like you.

I didn't look at that pdf until you posted a link... I just forgot to go back to their website.

Anyhow, Thanks again for your help. Now maybe the gecko people can help me on the resolution restriction of their products.

Allen

Hi freak brain.
I will answer what I can.
Geckos, from what I remember when I was setting up my control box, actually don't have an upper limit on the encoder count more or less. What is the limiting factor is the ability of the computer to generate the pulse stream fast enought to go anywhere at any type of speed. The standard is 500ct encoder in quadrature giving 2000 per rev. Your 1000 in quad, will be 4000/rev.

At a given pulse rate, you willl go 2 times slower. There are 2 ways around this. new encoders with 500 ct or the G340 servo drive with encoder multiplication which will allow you to get away with what you have.

The third option is to use a motion control card such as the smoothstepper or deskcnc card or other device that generates the step pulses and not the computer itself thru the pport.

Those 80v servos are a good match for the gecko's as the gecko has an 80 volt limit. I am assuming they don't have a ridiculus current rating. Max torque of a dc motor is direclty rated to its current draw. Limit the current and you are effectively limiying torque.

I looked at those renco encoders on ebay and will be buying some next week as they are a nice package and I several upcoming projects that will need encoders. Puls at $20 they are a bargain. If your motor has a 3/8 encoder shaft you can always turn the shaft down to 1/4 or I have read where people bore the encoder disc to a larger size. I have done this myself once and was very happy with the result.

Gecko accepts only single ended encoders, but you can use just the a and b pulses and ingnore the rest or get a differentil to single ended converter chip. Candcnc sellls these as part of his stuff or you can buy a chip from newarkinone or one of the other chip suppliers and do it yourself.

Al, some of the encoders have a ten wire connector comming out but they will only use 6-8 wires as needed.

Mike

Al_The_Man
10-18-2008, 10:25 AM
Al, some of the encoders have a ten wire connector comming out but they will only use 6-8 wires as needed.

Mike

I just wondered how come they came by ten? I could see if it was 12 or 13 like some of the Renco on ebay that have the BLDC hall effect equivalent output for commutation.
I have turned some of these out larger, you have to watch how much 'meat' you have on the boss, as going from 1/4 to 3/8 could be a stretch.
Al.

freak_brain
10-18-2008, 12:07 PM
Mike,

Thanks for all your help!!! I do appreciate it..

Well, I was thinking when I got these... cool, most of these guys are using 500 count encoders and I have 1000 count. Jokes on me huh, lol.

I attached the pdf file that Galil send me for my motors incase you wanted to look at it. The motors P/N is N34-150-1000. Like you said I think they will work just fine with the Geckos. As for the encoder, I had been wondering why one of the bullets for the G340 stated "Step-pulse multiplier for multiplying pulses by 1, 2, 5, or 10". I was thinking that it was like the micro stepping for stepper motors. So this will help me get the 4000/rev down to where the PC can manage it??

Also, I was wondering about using the cncbrain. Do you know anything about that and what it actually does? They seem to be saying that it handles the step/direction and at much faster rate than a PC but I'm not sure of this.

Oh, one last thing. How do I check the encoders to ensure they work properly?? I am a machinist and the shop I work at is pretty big. So I assume back in maintenance they have about all the test equipment. I imagine that they know but I would like to know for myself.

Al,

FIY

If you look at that pdf file it shows the wiring for a 10 lead ribbon on an encoder.

Thanks Again
Allen

Al_The_Man
10-18-2008, 12:31 PM
If you look at that pdf file it shows the wiring for a 10 lead ribbon on an encoder.

Thanks Again
Allen

Gotcha!
The easiest way to check the output is to power them up and use a 'scope, failing that it can be done with a meter, but on 1k counts and above you have to turn the motor shaft a slow as possible, but it can be done, on a 'scope you will see the relative quadrature pulses Between the respective A & B pulse, i.e. 90° apart, hence quadrature.
With a meter the output will rise from 0 to 5v.
If they are open collector Line Drivers, you will need a 1k resistor from each output to 5vdc.
Of course, if you wanted to get adventurous, you could hook just the encoder up to the DMC-700 and using a free terminal program from Galil, you could interrogate the card and it would show you a count of ±1000 for a single turn manually.
Al.

TOTALLYRC
10-18-2008, 02:33 PM
I like the idea of the cnc brain. It seems to me that most of the benifit comes when you use it in double closed loop mode. This means with encoders on the motors and scales on the axis. It can get expensive, but I understand that they are working on it. I would also get a total cost including any boards that might be needed for optio isolation and so forth.
I don't believe that you can use it with mach3, yet.


The smooth stepper is another nice motion controller but I think that you will need to use a breakout board in conjunction with it. Again, total price in your configuration is what you need to know, not just the opening price. Works with Mach3.

yes, the G540 is the way to go if you don't want to replace the encoders.

If you want, you could look at deskcnc, there controller/software package is nice. I use it on my router. Serial interface and will work with a usb to serial adapter. Won't work with Mach3 as far as I know.

If I rember anymore I will post again.

CarbideBob
10-18-2008, 04:11 PM
A couple of notes:
These are 150 oz/in servos not 900.
The 900 is a peak rating, drive a servo at it's peak for more than few seconds and it will be toast. Setup your amps to stay within the continuous ratings and they will live forever. I have over a hundred of these Galil motors in the field on customers machines.

The Gecko amps don't play well with high line count encoders. This has to do with how the PID loop is implemented in the amp. I think you will find tuning the amps to be challenging to say the least. If you are going to use the Geckos I would consider going to lower line count encoders.
Bob

freak_brain
10-19-2008, 12:29 AM
Bob Mike

Thanks for all your help and suggestions. I couldn't do it without guys like you, that is for sure!!

Here is what I think I should do.

I think I will get new encoders. For two reasons. First of all I feel a certain loayalty to geckos because of the support I got when I built my first machine. Marriss always answered my questions and was always available to help me out. Also, I know atleast a little about their products. The second reason is the fact that I know mach3 very well. For me, a guy that is not as technical as all of you, simplicity is big. In my confort zone I guess one could say.


Bob,

I thought these motors were always rated by their peak torque. I am obviously wrong. Thanks for the correction. It is good though to get the skinny on the motors. I was hoping they were in the range of average to good.

Thanks Again Everyone!!
Allen