What is the difference between servos and steppers?！

 Let me preface this by saying that I'm not very familiar with stppers so you should probably get a second opinion! Additionally, these comments are for systems >300 oz/in - systems smaller than that will probably be best off with steppers.

In general, servos have lower continuous torque but have the same amount of torque throughout their rpm range. Whereas steppers only have their rated torque at very low rpm, and will run out of torque fairly quickly, which means that you'll need a stepper with much higher static torque range in comparison to a servo. Steppers can hold their rated torque all day while servos are generally rated in continuous and peak - peak torque will be anywhere from 2 to 5 times continuous torque.

It used to be that servos were much more complicated to setup than steppers. With step-and-direction controls, setting up a servo is comparable to settings up a stepper. You do need to have an encoder (which means sizing the encoder) but you don't have to worry so much about torque curves.

In theory, a step-and-direction servo system should be more accurate than a stepper system since there is a closed loop between the drive and the motor. In practice, a properly sized stepper system will operate very similarly to a servo system. Please note - I am not referring to true closed loop systems here, with feedback to the controller. With a stepper lost steps are invisible, whereas with a servo system if there are enough lost steps the drive should fault.

In event of drive/control failure, a stepper will simply stop moving. A servo will probably go running at full speed until it hits something hard which can be pretty unpleasant especially with the forces involved in a typical CNC setup.

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