Wow I didn't expect that many responses in such a short a time ! Sorry for the late reply.
You are hinting that you have not ever tested your project as you developed it, Why not? If you had, you would already know the voltage and current requirements.
I have already made some tests, like one with 8 servos and 1 Arduino, or another with 1 servo per 6 Arduino. When I did the first test the 8 servos were connected to the Arduino 5V pin using a breadboard, the Arduino connected to my laptop, which was connected to the wall socket. For the second test the servos were directly wired to the 5V pin of their respective Arduino, the Arduinos were connected to the same USB hub, out to my laptop and wall socket. During the tests I had no idea what the voltage or amperage were, even though I have been explained many times how it works, I have never quite understood it, and just plugged everything in hoping nothing would go wrong. Except this time it's the final thing with 48 servos, 8 per Arduino, no breadboard and no laptop for power.
If I told you that the teeny-tiny vibra motor in your mobile phone can consume up to 100mA, would you revise your figures?
I took the numbers from the site I linked, however it seems like I misinterpreted it (I took current drain when idle). Thank you for letting me know.
The no-load current draw of the HS-55 servos is 150 mA at 5V, and the stall current is 450 mA.
The servos briefly draw the stall current (450 mA or 0.45 Amperes) every time they start to move. Do NOT attempt to power the servos from the Arduino 5V output, it will be destroyed immediately.
Power the servos separately and connect the grounds. If all 48 of those servos are moving at once, your servo power supply must be able to provide at least 10 Amperes (better if 20 Amperes) at 5V, or about 100 Watts.
The servos will be moving all at once. So I need to get a 20A 5V battery and connect the servos separately ? Would that mean that I need 3 different power supply, so 3 different cables connected to the wall socket (1 for the Raspberry Pi, 1 for the 6 Arduinos, and 1 for the 48 servos) ?
One Arduino and three 16-channel PCA9685 servo breakout boards (Adafruit, ebay) could have saved you a lot of work.
A Pi (no Arduinos) could also have driven those three servo boards.
I know and it is discussed on the project's github. We had to do it with the school's supplies, and it was decided that since it could be done with the Arduinos that we already have, we didn't need to buy new stuff. It was also decided to use both Arduino and Raspberry Pi so that we would learn more working with both of them. But you're right, it would have been far more easy.