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Introduction to AP04

1.   The AP04 range of fully integrated autopilots has been in service with numerous customers around the world since 2004. They have been successfully used in all types of aerial target and UAV platforms. Two models are available as shown:
AP04 AP04M
2.   The major difference between the two models is that the AP04 includes a built-in 900 MHz datalink, whilst the AP04M does not (it is designed to be connected to the Customer's external datalink). All references in this article to the AP04 apply equally to the AP04M unless specifically mentioned.
3.   Application.   The AP04 is suitable for all types of platform, including fixed and rotary wing UAVs. Other than servos and batteries (also an external datalink in the case of the AP04M), the AP04 is the only onboard system required to control a UAV and its payload.
4.   Major Components.   The AP04 is a complete autopilot, meaning that no other flight control computer or sensors are required for it to function as a flight control system. It includes the following main elements which are represented in the block diagram below:
  • Aerospace grade, waterproof, anodized aluminium housing with IP67 MIL-STD connector.
  • Twin redundant Flight Control CPUs.
  • A complete set of sensors, including an Air Data System (ADS), precision GPS, 3-axis gyros, 3-axis magnetometers, 3-axis accelerometers. The sensor suite provides the heading, attitude and velocity information required by the Flight Control CPU in order to control the UAV in all flight modes and to execute the required flight plan.
  • 900 MHz datalink (AP04 only).
5.   Fully Automatic Operation.   The AP04 is designed for fully automatic operation of the UAV, including auto take-off, flight plan execution and fully auto landing. For a full list of operation modes available, see KB article 'Basic AP Flight Modes'. AP04 can also adapt the aircraft for each stage of flight, e.g. deploying flaps during landing, locking nose wheel steering and deploying a parachute after a controlled deceleration of the engine.
6.   Safety.   In addition to built-in physical redundancy, AP04 has a variety of safety features:
  • Full range of alarms (see KB article 'Autopilot Alarms').
  • Protection against radio link loss: AP04 can be programmed to return to base and land automatically.
  • Survival of sensor failure: AP04 uses advanced estimation algorithms that greatly enhance navigation accuracy and make the AP04 capable of surviving several sensor failures, e.g. in case of loss of GPS signal, AP04 will continue to navigate in inertial mode.
  • AP04 can be configured to provide redundant servo outputs (e.g. two separate ailerons on each wing).
  • AP04 ensures that the flight envelope of the UAV is never exceeded (e.g. no more than 2G in a turn). Manual override capability (using an R/C type joystick).
7.   Payload Control.   See KB article 'Introduction to Peripherals'.
8.   Software Update.   See KB article 'Software Update Tool'.
9.   The AP04 family of autopilots were phased out at the end of 2017. Check out our other autopilots for alternatives.