Powering 5 servo motors.

Hello everyone, I am new to robotics and making a small project involving 5 servo motors (SG90 micro servo) operating voltage of 5 volts. I am confused that to power all servos separately from arduino should i be using two 12volt batteries in series or is there any other alternative possible for the power management. The robot will be wireless controlled bot so I might use an Xbee shield as well. so i am guessing seperate power supply will be required for the arduino uno and the shield. Please suggest the optimal batteries i should go for. Thank you

The problem with servos is they draw big pulses of current, perhaps 1A each when they move or when their movement is resisted - this means the battery voltage will droop or drop-out briefly as this happens (especially as the batteries get low on charge) and any microcontroller running on the same supply will crash or reboot all the time - unacceptable.

So you may want to consider a 6V pack just for the servos. If your main power is 12V you could have a DC-DC converter with a large enough current rating to drop this for the servos. In fact you might get away with doing this for the Arduino as well, using another 5V DC-DC converter as the 12V supply can then dip to 5V or so without losing power to the microcontroller - the DC-DC converter helps isolate the delicate circuitry from the spikes/dropouts and noise generated by motors and servos.

I find you always seem to have more effort sorting out power than you would like, it seems such a trivial thing, but poor/inadequate power supply will always create grief...

It sounds like you're assuming that you need 5V per servo and are hoping that the 24V you can get from two 12V batteries will provide it. This is not true - you need 5V irrespective of how many servos you have - although you'll likely have substantially fewer if you do hook them up to a 24V supply.

What's important is that your battery pack can supply enough current - as MarkT says - budget one amp per servo.

Please suggest the optimal batteries i should go for.

Batteries made for RC hobby equipment might be a good start. Servos work best when supplied 6v instead of 5v. Search ebay for UBEC voltage regulators, as they are made for use with servos.

The pic attached shows 3 servos hooked up…

servo power.png

zoomkat: Batteries made for RC hobby equipment might be a good start. Servos work best when supplied 6v instead of 5v. Search ebay for UBEC voltage regulators, as they are made for use with servos.

Actually - servos work best when they are supplied with the maximum voltage they are spec'd at. In most hobby servo cases, that is 6 volts (generally the range is something like 4.5 - 6 volts). In some cases though, a servo may be spec'd for a higher voltage (these aren't as common, though).

LiPo battery packs have become the new standard and thus pretty cheap. They do however need a certain type of balanced charger (Imax b6 for a cheap example). If you get a 2s Lipo it will be specced at 7,4v (8,4V when fully charged) and they are availible in everything from around 100mAh to 5k+. There are several UBEC's and also voltage regulators which can get the voltage down to 5 or 6v depending on what you desire, the 7805 series and similar.