I would agree with @Sunit_Pal regarding the Pixhawk with the current ArduCopter firmware does NOT support RC flying the way you intend to fly (acrobatics) especially without a flybar. I agree that the pixhawk offers some great safety nets that would keep you out of trouble but the flying qualities for a flybarless heli with the Pixhawk are no where near that of a 3 axis gyro system. The issue comes down to the ability to tune the PID controller with helicopters is limited because they are more sensitive to aircraft oscillations feeding back into the servos causing a resonance (oscillations that can damage your heli if they get too bad). This is different from isolating the pixhawk from vibrations. Even if you minimize vibrations on the Pixhawk with vibration dampeners, you will still encounter the limitation with the PID tuning. Hopefully in a future release of the Trad Heli firmware, they will add a notch filter that will help prevent these oscillations from getting back into the servos and cure the problem. Read my post on Techniqe to expand roll and pitch rate pid gains without instabilities for more information. I have successfully integrated notch filters into the PID controller and have achieved flying qualities in acro mode that are better than a flybarred heli. I can’t compare it to a 3 axis gyro system cause I’ve never flown a heli with one.
I hate to turn you away from the Pixhawk but until the developers implement this fix, you’ll be wasting your time and will be very frustrated. Now many of the Pixhawk users have integrated a 3 axis flybarless gyro with the pixhawk with some success. I think it will still achieve your goal of having the safety net with the pixhawk but the gyro is stabilizing the heli. There are a few discussions that go into detail on how to integrate the 3 axis system with the Pixhawk.
Good Luck,
Bill
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