servo basics

[eloid]

can someone please shed some lite on this thought, i was told that most servos are for the most part just dc motors.... what difference?

Im Looking for quality servo, motors with good torque curves.. i seen most offshore cheap motors dont show nor compare to quality (mainly) name brand motors with high torque / rpm rates.

any recomendation for a 5x9 table dual y drive set up something like shop bots? but I like servo encoder better then stepper/ less noise/ faster most cases etc

[unterhaus]

steppers are easier and usually cheaper. I like servos better myself, and that's what I use, but I realized long ago that for what I do, I don't need them.

There is a fairly steep learning curve for servos, and probably you will not learn enough on a forum thread to get you up to speed. If you're serious about it, my recommendation is to look at brushless, brushed servos are not as easy to get nowadays.

[eloid]

i was looking at http://homeshopcnc.com/page4.html
For Nema 34 850 oz/in Peak Torque

I like to get some opinions on the specs for this unit, I dont have torque
cures to see how it performs with all rpms. Would like to get feedback if any one who uses them. Planing on building 5x9 table shop bot like unit with rack and pinion dual drive on y axis. planning on using a gearbox 7.2:1 on y and x.

this is the spec from the above link.

Nema 34 850 oz/in Peak Torque 72VDC Servo:
HEDS-9100 optical encoder

$199.00 with standard encoder

$159.00without encoder

see attached picture: Servo with meltal case Encoder

Specifications:

- skewed rotor design - maximum operating speed: 4200 rpm

- continuous torque: 270 oz/in - torque constant (KT): .1757 N. m/am

- peak torque: 850 oz/in - voltage constant (KE): 15.71 volts/100rpm

- terminal voltage: 72 VDC - resistance: 85 ohm

- continuous current: 8.5A - inductance: 2.35 mH

- peak current: 38A - weight: 8.8 lbs


- inertia: 3.39 kg.cm^ - 7 inches

[The President]

Any motor type can act as a servo if it can provide position feedback. Brushless servos are most common in industry, but brushed DC is also used. One major advantage that brush servos have is they need relatively simple drivers, whilst brushless need more complex ones. Incidentally, you can use a stepper as as servo just by matching up an encoder to it. These are not as expensive as they used to be.
My suggestion is that you try to get some good literature on motor types before purchasing.

[Kelinginc]

Pls check here
http://www.kelinginc.net/ServoMotor.html
One cuver for KL34-180-90 is attached. If you need more tested data, email me at support@kelinginc.net

[routerman]

The offshore servos work very well, and seem to do the job just as good as a Baldor or others. Ive used them with excellent results.
Get a high res encoder 1000 lines+ to get smoother responce on a 2 pole motor.
A shopbot has to be the bottom of the barrel when comparing cnc routers. I hope you build a sturdier machine than that !