Request to go over this code

Hello,
I am currently working on a project trying to build a VTOL aircraft.I am at the moment stuck at the hovering part of it.I am using the arduino mega, and an mpu 6050 with the library from jeff rowberg, as well as the pid library.
The configuration of my aircraft is in the attachments below along with the code i am working on. I would request anybody who has worked in this area(quads, other types of vtol) to please view the code and tell me what area i am going wrong.Is there some problem in the code, or is it that i am not able to tune the pid controller.The code attached is only for pitch balance, and the same logic follows for what i am doing for roll and yaw.
Really looking forward to getting it to fly and any help will be greatly appreciated.
Thank you for your time
Vishwajeet Karmarkar.

pitch_controller.ino (5.03 KB)

You can set the PID output range to allow both negative and positive values. The default range is 0 to 255 which is good for direct control of PWM outputs. That should greatly simplify your code that detects which direction you think the correction should be and making it so.