High current battery-to-5V supply for RC system

Discussion in 'Embedded Systems and Microcontrollers' started by petiaccja, Jul 8, 2014.

  1. petiaccja

    Thread Starter New Member

    Jul 8, 2014

    The Project
    I'm building RC vehicles with a Raspberry Pi, basically replacing the reciever by the RPi.
    It consists of the following parts: Raspberry + WiFi + webcam, servos, electronic speed controllers (ESC) + DC motors.

    The Problem
    The whole system need to run from batteries. I'm using LiPo batteries, ranging from 2 to 4 cells (7.4V to 14.8V nominal). Most of the things need 5V to operate, including the Pi, servo motors and USB devices.
    Current draw is as follows:
    - Raspi: 700mA
    - servos: 500mA each one
    - USB: 1000mA
    It adds up to about 3.7A (for 4 servos).
    How can I feed all those things from the battery?

    USB devices
    The Raspberry cannot feed it's own USB ports for more than 200mA. My devices draw way more than that, so I want to hijack the USB power pins and connect them to an external supply, while leaving the data pins as they are. I guess it does work, right?

    What I have so far...
    I tried L7805 regulators, but they get too hot, and are very inefficient. I'm looking at DC-DC converters, since those are quite efficient, but also expensive and their throughput is far from 4A.
    Can you suggest a converter that suits my needs?

    Another option is to fall back to the ESC's BEC feature to feed servos, leaving only the Pi and USB to bother with, but that's still at least 1.5 amps. I can be happy with that since it's probably cheaper, but it would be great if it didn't need to have an ESC.
    This is rated for 1000mA and costs about 14 USD. Current limitation is 2000mA if I'm right. Do you think it would be a good choice, and is overdriving it to 1.5 amps feasible?