connecting to servo

Hey all. I just bought a GM4 'gear motor' servo. Says 325.1:1 6v and should run on 6 volts.

Just wondering if I need to do anything to protect from back emf like a normal motor or if it's all handles in the internals? It's only a two wire servo. Looking in the case I can see a cap across the motor but nothing else. Just wondering because I don't want to destroy my arduino.

Also at 5v it says it unloads 63mA. Can a PWM pin power than?


It's only a two wire servo.

I would think of it just as a DC motor. You will have to find out it's maximum current specification and then figure out how you wish to control the motor. If you need bidirectional control you will need a H-drive controller, it just single direction then PWMing a power transistor would work. Even at the unloaded 63ma specification you can't draw that much current from a Arduino I/O pin, plus one really should design their motor drive circuits with either current limiting protection or the ablity to supply locked rotor current.


yeah shit i guess it's like I just bought a $20 motor. and I don't have any diodes (I guess an LED would pop if I tried to use it)

what would be the simplest way to take power, say from a bettery pack plugged into the arduino?

what kind of power would I get from Vin if it's connected to USB?

Then I could just use a transistor, no?

Well, here are the specs for your motor:

and they say it can draw about an Amp when stalled. That's more than you can draw from a USB port, and a properly-designed USB hub will shut off the power when that happens.

If you just want to watch it spin, you could hook it up with a small transistor (like a 2N2222), because it doesn't draw much current when it's not doing any work. But, it you want to do any actual work with it, you'll need a separate power supply, and something hefty (like a TIP120, a power FET, or a proper motor-driver IC) to run it.

There's lots of info on controlling motors in the Playground:


Thanks for the links. There's a lot of reading I need to do. I'm a Softy not EE, so I'm bad at this.

With regular motors (since I got one from a floppy drive) if I'm running controlled it through a transistor do I need to protect it from back EMF? and would back EMF destroy the transistor or is it possible it can also so damage to the pin connected to the base?

Yes, you need a diode for anything like a motor, relay, or solenoid that has a coil in it (You don't need one for an RC servo because you're not connecting to the motor, itself: the signal goes to electronics indie the case that handle the motor).

If the back EMF pulse has enough energy, it is possible for it to flow back through the transistor and damage the CPU. I'm not sure how likely it is, though, because I was warned about it early on, and have never made the mistake of leaving the diode out.