High power servos draw a lot of current - a set of four 8717 servos can often be pull 12 amps! The SK-PW1 Power Bus was designed for up to 20 Amps of continuous current. Also, six heavy servo cables can transfer a lot of vibration to the SK720's acceleration sensors. High vibration will degrade the quality of the self-levelling and flight log playback. For these reasons, for 600 size helis and up, we recommend using a servo power bus with the SK720.