DJI F550 + Apm 2.6 can't throttle but arm

Hello everyone, i am new in this forum and in this world (copters), i recently bought a dji f550 kit with ardupilot flight controller. I supose i build the kit ok and connect the esc to the outputs in the apm. The problem is when i arm the motors in estabilice mode, i can’t throttle until y press up or down the pitch button. When i do that the motors start to spin, but not all. What is the problem? My RC calibration in mission planner is ok (theorically).

PD: Sorry for my poor english. I speak spanish and thanks to all. i’m very confused.