Originally Posted by
Torchhead
The stepper VS Servo debate has been waged ad infintium on this and other lists. There are arguments in both directions. I run machines I have built with steppers and others with servo's. The general argument is that servo's have what is called a "closed loop" and any loss of position outside the range of error (normally 128 counts) results in a fault that stops movement. They are also quieter and smoother (although with modern micro steppers like the Gecko that is less of an issue). A falicy exists that servo's are better because they "correct" for positional errors but the fact you are getting postional errors at all indicates something is wrong, so how far do you want a servo to actually correct before it decides it's trying to push against an obsticle and burning up the motors? A loss of position on either type of system indicates a problem in either the design or the work being done (working outside the limits of the machine). It needs to be physically corrected rather than compensated for. Properly designed and used steppers do NOT "lose/gain" steps.
You can get faster speeds and higher torque from a similar sized servo. Steppers lose torque as RPM increases whereas the torque for a servo is actually greater at higher speeds. Conversly steppers work better at low RPM than servo's.
So now that you are confused I offer this: Buy the system you are most comforatble with. If you use you table a lot in production the added cost is easy to rationalize. If you were doing the design it (would be) harder to build a stepper that does not lose steps than a servo, but in the process of buying one from a vendor that issue goes away. They have done the engineering, testing and have working machines in the field under varying conditions. If your primary intent is just plasma cutting I think a (properly designed) stepper system is just fine. Use the money to invest in a good THC solution for plasma.
Just my opinion and I have the whip marks to back it up (:-). BTW My home built plasma is servo's on X&Y and stepper on Z.