View Full Version : drive control system

22-05-2011, 03:37 PM
hi this might be a noob question but whats the diff between stepper motor and controller setup vs servo motor and controller setup. what sort of setup is needed for each and what are the pros and cons of each system.

22-05-2011, 07:30 PM
A quick Google search will find you plenty on the topic, but I'll briefly summarise.

The fundamental difference is that a stepper motor has no feedback, whereas a servo system does. This means that to control the stepper motors you send the drivers a signal to specify the direction, and a pulse for each step. This means that you just need motors, drivers, power supply and computer to run them. Servos however use an encoder to provide the feedback, so you need that too. They are also a completely different type of motors electrically speaking.

Servos in general deliver much more power than stepper motors. The torque (and thus the output power) of a stepper motor decreases dramatically with increased rpm. Servos are much better in that respect. Servos will not loose position as easily as steppers due to the feedback loop, however a well designed stepper system won't loose steps either.
The resolution of servos is generally higher than steppers, 2000 'steps' per revolution versus 200 for steppers. You can use microstepping (stopping between steps) on a stepper motor to get better than 200, but above roughly 800 it's just not accurate (in general).

Another thing I should mention is safety. Servos can 'run away' if something goes wrong with the signals, but again you can find out what to do easily enough.

If you can afford them and the application warrants (eg about 100W required from motor) it then get servos. I've not got them as I can't afford it!