Hi,
Am new to quadrotors and its my final year project. I have done a long research that took me 6 months to understand each individual part and how it operates.
1- Turnigy Talon Frame (Quadrotor)
2- Q-brain 4x25 A Esc (UBEC)
3- Ardupilot Mega 2.6
4- Frsky V8FR-II HV (Receiver) + DJT AF Module
5- 1100 Kv Turnigy Brushless motors
6- Turnigy 9XR (Transmitter)
The problem is when i arm the APM everything is ok. The motors do not spin so its normal at lowest throttle but, when i turn the throttle up to 20% the motors still not spin at all. When i turn the throttle up to about 20% the motors suddenly spin in very high speed about (70%). I know its high speed because in the calibration mode the speed varies constantly unlike in normal flying mode.
Notes:
1- When i calibrate the motors response is great and i calibrate the ESCs through APM ( Input receiver wires ) (Output ESCs signal wires).
2- I tried changing the gains of the throttle in the parameters list. ( nothing changed ).
3- When spinning the motors through the ESCs directly they response very well the same as the calibration mode while connected to the APM.
I have been trying to solve this problem for 3 weeks now !!! 
, If needed i can make a video showing the problem.
Thank you