Archived:APM 2.5 and 2.6 Overview — Copter documentation
Ardupilot Mega APM 2.8 2.6 Flight Controller with Anti-vibration for Racing Drone FPV Quadcopter Arducopter RC Model - AliExpress
APM2.8 ArduPilot Mega APM APM2.8 Flight Controller Board with Case for RC Quadcopter Multicopter F450 F550 S500 S550 ZD850 ZD550 - Price history & Review | AliExpress Seller - Readytosky Official Store | Alitools.io
ArduPilot Mega - Arduino Mega compatible UAV Controller - GPS-10294 - SparkFun Electronics