Motor selection advise needed? Servo or Stepper

Ok, now I have got the bug to build a CNC router table and could use some advise on motor selection and drive selection.

I am hoping to build either a 4' x 4' or 4' x 2' machine. I plan on using a either small router motor unit or a edge trimmer unit for the cutting power. Most of the construction materials will be aluminum and steel tubing for the main frame structure. I will be using ballscrews for the Y and Z axises and most like a rack and pinion system for the X axis unless I can find a good deal on some longer ballscrews. I want to be able to cut wood, MDF, foam, plastic, carbon fiber and maybe some thin aluminum plate. Will probably be using V-Rails for the longer X axis and linear rails or Thompson bars and pillow block bearing for the Y and Z. The mechanical parts I won't have too much problems with since we build 3 to 5 axis scanning systems were I work as a machininst. It's the electronic parts I am a newbie to.

(1) Do I go with servo motors (pricy but more reliable I have heard) or use stepper motors?

(2) Should I use AC or DC motors and what voltage?

(3) What is the minimum amount of torque the motor should have?

(4) What is minimum recommended resolution of the encoder or stepper required?

(5) What type of motor drivers should I get? (easy to work with and setup)

(6) Since I plan to program in G-Code what controller unit should I get?

As for my budget, it is limited like alot of us hobbist but I would rather put the money into the most important part of the machine in my option. Good reliable electronics and motors. I will most like want to get all my motors, drivers, powersupplies and controller first so I can at least get them hooked up and start playing around with that part.

That is all the questions I can think of right now. ;)

Any advise anyone could offer would be appreciated.

Thanks,
Carl

(1) Do I go with servo motors (pricy but more reliable I have
heard) or use stepper motors?

Well, someone said that if you need motor power of less than 100W, go with steppers, for 200W and above, use servos, and in between, both is ok. I think this is from a cost perspective.
Servos give you more speed and *can* give you better accuracy, if you go for a professional system (expensive or very time consuming to buy and set up).
The Gecko-style step-and-direction servo controllers should give you about the same performance as steppers for the same amount of money. Perhaps a bit more speed?


(2) Should I use AC or DC motors and what voltage?

If this is for a production machine that will be used many many hours, go for AC motors. They are much more expensive (or at least the AC servo drives are more expensive) than DC motors, but last more or less forever. They are also smaller, require no brush maintenance, etc etc.
I hope to be able to use AC motors in the router/milling machine I'm building, but I've been on it about 6 months and still haven't found suitable drivers (at a price that won't blow my budget away) for the motors...


(3) What is the minimum amount of torque the motor should have?

You'll have to estimate the cutting, friction and acceleration forces and then calculate this. You can find some formulas in my thread: http://www.cnczone.com/forums/showth...&threadid=1979. And more formulas here:
http://www.cnczone.com/forums/showth...2883#post22883


(4) What is minimum recommended resolution of the encoder or stepper required?
Depends on the resolution you need. Also if you use step/dir parallell port signals, don't use too high resolution since this will limit your top speed. If your computer/CAM program can output 20000 steps/s (20 kHz) then your top speed is 20000*resolution (in "resolution units"/s).


(5) & (6)
Someone else will have to answer this since I don't know much about it.

Good luck! :)

Arvid