How do I calculate required voltage and current for multiple servos?

Question

I'm looking to power 3 servos and control them with an Arduino Uno.

Could someone please explain to me, not just specifically for this, how I can work out how much voltage and current I need to power several motors at maximum power? I've heard that it doesn't matter how high of a current I supply as the motors will only draw what it needs from the battery. Is this true? If so how do I know the minimum current I must supply? As for the voltage, I've heard things like for a 6V motor you can use 6V to power up to 4 motors. If this is true, why is 4 the cutoff? And does that mean I need 6.8V for these?

Also how do I choose which type of battery to go for? This needs to be portable so I can't have mains connections, so how do I choose between the AA type of batteries, LiPo or Nickel, etc..?

Sorry for the basic questions, just trying to build up from the foundations.

Answer 1

The specs for the servo indicate about 2A at stall, with a supply voltage of 5 to 6.8V. You can use any voltage in that range regardless of the number of servos you’re using. If all of the servos could operate at the same time then you’ll need a current capability of 2A per servo, so 8A for 4 servos (plus a little bit for the Arduino). You could use 5 NiMH cells giving about 6V, but 8A is quite a bit for AA cells. 18650 lithium cells have a much higher current capability (some up to 40A) but the voltage isn’t ideal to use directly so you’d need a DC-DC converter. Unless you need maximum servo torque you might stick to 5V which can power the Arduino directly.