Originally Posted by WoodSnarfer 1. What makes a DC motor worthy of being called a 'servo'? Is it just the fact that it'll spin at around 3,000RPM, it has adequate HP, and you can stick an encoder on it good enough? Or are there other specs it needs to meet (duty cycle?). |
I think servo motors are often made to have a small rotary inertia to be able to change speed fast. Noah also made some very good comments about the placement of the brushes on brushed motors. The term servo motor I guess should also mean the motor is good quality with low cogging - the rumor has it you should be able to run a 60 V servo motor with a battery (it should not "stick"). I believe this - my 200 V AC servo motors aligns quite forcefully with the field produced from a C cell battery (as AC motors they won't spin, of course).
A motor in itself is not a servo. What turns it into a servo is the drive - a servo is just something that "serves" you; i.e. it goes where you tell it (or as fast as you tell it etc) and it also makes sure it does that by feedback. To do this it needs a drive/controller of some kind.
Another difference is that a "generic" small 12 V motor is made to run at 12 V. A servo motor marked 200 V might burn if you just hooked it up to a 12 V supply! It needs to be hooked up through the drive to limit current.
Originally Posted by WoodSnarfer 4. I also see a lot of 90VDC motors, and a few 'in between' (40V to 60V). If the other specs look right (RPMS, HP), can they be used? Or, will the power supply requirements be too great? |
A higher voltage motor is often more efficient (less copper losses). Higher voltage means less current for the same power, and current makes things hot. So the power supply will probably be cheaper to build for a higher voltage motor, but it's also more dangerous. So I guess in the end the suitability of the motor depends on if you can find a fitting drive for it and if you feel comfortable with the voltage required.
Arvid