[cnctoolman]

Okay I got the mill, getting the ballscrews,pre-loaded nuts(5/8") on order. Now I have to decide on which controls to go with. If you had your choice which would you go with and why?

Chopper board running atleast 250oz. stepper motors unipolar.

Chopper board capable of running bipolar motors ( probably the popular 270 oz. motors)

Or 3 Gecko servo drivers running servo motors. I found these motors at a decent price and think they would work. Specs are 23 frame, 250 oz., 36 VDC(12-60VDC), 2850 rpm, 4.3A, with 1000ppr quadrature encoders. Would need to gear them down.

This site is given me the bug and I am still going through alot of the old post learning. Gotta find the one again for the gear conversion on the servo/ballscrew ratio.

Thanks for any opinions

[JFettig]

I have steppers and gecko 201s, I saw those servos and I am extremely tempted but have to resist.

I am building another for a friend(and a kit to possibly sell) that will use the 270oz-in motors.

Jon

[balsaman]

1000 cpr is a bit high. You may need to go gecko 340's with those.

Eric

[JFettig]

1000 pulses per revolution on a 5tpi ballscrew is gonna give you the resolution of .0005", 1:2 ratio thatll give .0001" which is good. at 25000 hz they will run 150ipm(750rpm at the screw, 1500rpm at the motor).
Im not sure if they will run that high, but thats just the calculations.
Jon

[cnctoolman]

Thanks for the replies

[cnctoolman]

One question I have to ask. I have looked at the hobbycnc package( 3 200in-oz. motors, 3 axis board) and have heard/read conflicting responses. That the 200in-oz. motors aren't enough and others say they are perfect for this size mill. So which is it?

[JFettig]

200oz-in motors are cutting it really close, especially for the z-axis, I dont know how well it would be able to lift it. Im sure they will work. What is your goal for this machine?
Is it just to cut out parts or is it to cut out parts fast?

Jon

[cnctoolman]

The main goal of it is to cut parts, but not necessarily fast. Plan on mostly just engraving aluminum(6061 T6) frame plates that I make for people. Also for me to get my feet wet, I have become quite " enamored"( I think I spelled that right) with the idea of building my own cnc. I am a glutton for learning.
I am trying to decide which way to go so I can get a realistic feel of what to expect performance wise. Right now I am leaning more toward the servo/Gecko set-up. But want to investigate everything.

A little background on me is I use/have used Kitamura Mycenters, Bridgeport retro's,Prototrak M3 bed mills and such on a daily basis. My main function is Tool & Die( going on 10yrs) mainly in stamping, draw dies. Where I work I use GibbsCam daily. So machining isn't new to me, all the electronics that I am finding here are( pertaining to building my own cnc). The mechanicals are'nt though.

I find alot of help in what others have experienced and try to use that in my decision making, that's why I am asking alot of questions and reading alot of the old posts.

[cnctoolman]

May have it narrowed down:

3 276in-oz. motors from Auto-direct and 3 Gecko 201 drives - 470.00

3 of the servo's above and 3 Gecko 320 - 500.00


Prices basically the same. Uggh the decisions

[motomitch1]

servo's all the way, maybe you could set up a vote or poll

[balsaman]

1000 pulses per revolution on a 5tpi ballscrew is gonna give you the resolution of .0005", 1:2 ratio thatll give .0001" which is good. at 25000 hz they will run 150ipm(750rpm at the screw, 1500rpm at the motor).
Im not sure if they will run that high, but thats just the calculations.
Jon

Gecko 320's will multiply your encoder count by four, so it takes 4000 pulses to turn it once times 5 per inch times 150 IPM divided by 60 seconds is 50,000 hz at direct drive, 100,000 hz at 2:1 ratio. 25,000 hz will only get you going 35.5 IPM at 2:1 ratio. Unless those are 250 CPR encoders at quadrature...

Eric

[cnctoolman]

So if I go with the servos then I should look to replace the encoders with ones that are 250cpr then? That or step up to the 340 gecko's.

[JFettig]

250 CPR quadrature encoders put out 1000ppr, 1000ppr encoders put out 1000ppr
I dont have enough experience in this area, but thats what I know from what I have read so far.

Do the geckos actually multiply them by 4 or are those the quadrature encoders that are different like that?

Jon

[balsaman]

250 CPR quadrature encoders put out 1000ppr, 1000ppr encoders put out 1000ppr
I dont have enough experience in this area, but thats what I know from what I have read so far.

Do the geckos actually multiply them by 4 or are those the quadrature encoders that are different like that?

Jon

The above is correct, I am just trying to make sure it's understood.

The geckos don't multiply it, but counts each rising and falling edge of the pulses, so a 250 Cpr encoder needs 1000 pulses from the PC.

If the encoders are 250 Cpr, you are fine, if they are 1000 Cpr, then get the 340.

Eric

[JFettig]

Balsaman, when I was searching around, I found that CPR is Counts Per Revolution, PPR is Pulses Per Revolution, basicly the same thing, although an encoder in quadrature is going to be different, This one doesnt say if it is, so I am assuming it is not I am pretty sure the guy selling them knows what he is talking about, Dan Maunc? not quite spelled right but he sells lots of motors.


Jon

[Torsten]

Encoder counts are usually given in quadrature so a 250 encoder requires
1000 stepsignals to make one revolution.

[JFettig]

All encoders arent quadrature are they? Thats one thing I have been wondering about, I havent been able to figure that out, I was about to order some 500cpr encoders but I wasnt sure if it woudl have been 500 pulses per rev or 2000pulses per rev.

Jon

[lerman]

All encoders arent quadrature are they? Thats one thing I have been wondering about, I havent been able to figure that out, I was about to order some 500cpr encoders but I wasnt sure if it woudl have been 500 pulses per rev or 2000pulses per rev.

Jon

From a practical standpoint, encoders are either absolute, or quadrature. You might find a non-quadrature encode to use as a tachometer, but it probably wouldn't have that many counts.

500 CPR will "probably" have 500 lines. Each line will cause two transitions (one from light to dark and one from dark to light). There will be be two detectors, oriented 1/4 cycle apart. So, first one will see a dark to light transition, then the other will see the same transition (for motion in a constant direction). You don't get 2000 pulses per rev, but the hardware does generate 2000 transitions per rev.

Ken

[cnctoolman]

Going with the servo motors. One more thing down, many to go.

[cnctoolman]

Gettting ready to get the servo's and when I reread the description they are quadrature encoders.