RE: Futaba 3PM-2.4G, do I need a failsafe?
sure you could but if you were to upgrade to digital servos you might as well do the 6v conversion as well. that way you get the best performance from your servos (torque and speed). for a flat pack for a revo with 6v can be had for $20. that will even wake-up the stock servos.
research though because i know that some of futaba's digital servos are supposed to only run on 4.8v (dont know why).