When is a motor shield/external power supply necessary for servos?

I want to do a robot using 2 continuous servos (5V, 15-200 mA) and 2 smaller regular servos (5V, no current info, but its this one: EMAX ES08A Servo Specifications and Reviews).

My question is, at what point (current load, number of servos, etc.) do you need to use a motor shield or some other method to control the servo?

Thanks in advance!


I think that the "limit" is 3 (or three-ish.)
All you need is a 5V source exclusively for the servos; you don't want to run 4 from the Arduino's 5V, that's excessive demand for it.

Thanks for your response!

Just a little bit of a curiosity follow up question:
What makes you say 3-ish? Does the PWM get a little imprecise when the arduino is running a bunch of them? Sorry for all the questions, I'm new and just want to make sure I understand.

It depends on the “actual” current each motor needs.
3 motors may be at the tipping point that the Arduino can drive.

Best place I've found to read about servo powering is DuaneB's stuff

So yes the decision on external power or Arduino 5v is a current thing, but it's so little hassle to hook servos up like DuaneB shows, it's worth doing as a matter of course even for 1 imo.

From a control (as opposed to power) point of view, the servo library has plenty of connections for your 4.....