Powering Arduino Mega 2560 from a Raspberry Pi Usb I have a Raspberry Pi B+ running 7x24. I have to connect an Arduino Mega 2560 to its USB. The Arduino has only one nRF24L01-PA-LNA powered from its 3V3.
Can I power the Arduino from the Pi's USB?
If you are powering your RPi from power supply 5V/2A at least there should be no problem. USB hub on the RPi should not give more than 500mA to power Arduino. Also there is a fuse on Arduino's board to prevent any damage from USB power. 

Check both Arduino and RPi schematics for more details about modules used there:


Arduino
Raspberry