AP4 GPS AutoPilot User's Guide



  • Features
  • Installation
  • Operation
  • Payload Programming
  • Aerial Photography
  • Radio Failsafe Function
  • Troubleshooting

    • Features

  • The AP4 is a complete aircraft autopilot system for radio control vehicle use.


  • Can be flown on almost any aircraft (gas or electric powered) with a wing area greater than 300 square inches


  • Controls up to three servos: Rudder, Elevator, and an optional Payload Trigger


  • Receives gps navigational data from any NMEA-0183 protocol gps (Garmin Etrex, Geko 201/301 are recommended.)


  • Precise flight paths are flown by simply programming multiple waypoints into your handheld gps unit


  • Up to 20 waypoint triggers can be programmed to activate payload such as cameras for taking multiple photos at different angles, dropping payload, etc.


    • Installation

    1. You will need an aircraft with at least 300 square inch wing area, a 5 channel radio system, an NMEA-0183 compatible handheld gps (Etrex, Geko 201/301, etc.), a gps data cable that fits your gps, two 6-volt receiver batteries (or a BEC receiver with one battery) with JR/Hitec/Z connectors.

    2. Choose a location inside the fuselage of your aircraft to mount the autopilot. This should be near your receiver unless you will use servo extension cables, and preferrably near the center of gravity to maintain original flight performance.

    3. Choose a location for your handheld gps. This should be located such as not to obstruct the satellite antenna's view of the sky, but anywhere near the center-of-gravity may work as long as you test satellite reception to confirm antenna placement before flight.


    1. Rudder Servo Output
    2. Elevator Servo Output
    3. Payload Trigger Servo Output


    4. Check which channels of your receiver are connected to your rudder and elevator servos and plug the autopilot's rudder and elevator connectors to the corresponding channel socket on the receiver (be careful to get the polarity of the connectors right or damage to the autopilot and/or receiver may result).

    5. Connect your rudder servo and elevator servo connectors to the autopilot's pin header sockets (observing polarity). the ground lead (black/brown) should be facing closest to the edge of the board.

    6. Find an unused switch channel on your radio system that can be used as the autopilot on/off control switch. Determine the corresponding channel socket on the receiver and plug the autopilot's on/off connector to it.

    7. Set servo reverse jumper switches if need be to correct rotation direction. If your plane's rudder turns clockwise (when looking down at it) when your rudder servo turns clockwise, then leave the rudder reverse jumper in place, otherwise move (or remove) the jumper away from the microprocessor. If your plane's elevator moves upward when your elevator servo turns clockwise, then leave the elevator reverse jumper in place, otherwise move (or remove) the jumper away from the microprocessor. If you have a payload servo that you wish to turn counterclockwise when activated, then leave the payload reverse jumper in place, otherwise move (or remove) the jumper away from the microprocessor.

    8. Connect a 6-volt receiver battery (5 or more Nicad/Nimh cells) to the power input lead (brown/white wire), observing the correct polarity. The white wire is positive (+), brown wire is negative (-).

    9. Connect your gps to the autopilot's RS232 port and test the system to verify correct functioning before flight.

    10. Adjust the gain and travel limits of the elevator and rudder servos to match the stability of your airframe using the blue potentiometers. These should be set conservatively for now. Rotate all four of the blue potentiometers counterclockwise almost completely using a small screwdriver. The servos may not seem to turn at all (with autopilot switched on from Tx), so raise the gain 1/4 turn and then raise the travel limit pots until you get only a few degrees of turn of the control surfaces (when the gps is sending correction data). Do not use more than 1/4 turn from CCW on your initial test flight. This will insure the correct operation of the craft until you verify in flight tests if the plane can make sharper turns.


    Operation

    1. Turn on your radio receiver, transmitter, gps, and autopilot.

    2. Program a route with waypoints into the gps and confirm that the route is a safely flyable route within the flight range of your aircraft. Set it to follow the route from beginning waypoint to destination waypoint (consult your gps owner's manual for specific instructions). Programming can be easier using a computer with mapping software and uploading a route into the gps through the data cable.

    3. Check satellite signal quality, number of satellites, and consistency of data. If less than 5 satellite signals are available or current positional data seems inconsistent, do not fly!

    4. Start your engine/motor and check the controls to verify power and signal.

    5. Takeoff and fly to a safe altitude and level off before switching on the autopilot.

    6. Switch on the autopilot and watch to see if the plane is tracking correctly

    7. When you are ready to resume control of the aircraft, flip the autopilot ON/OFF switch off and begin flying as usual.


    Payload Programming

    1. There are 20 different waypoint ID numbers that will activate the payload servo (320-339). Start by programming a multiple waypoint route to fly into your gps.

    2. Choose a leg of the route to place the trigger waypoint into the route. Remember that the autopilot will trigger when the gps displays the "destination waypoint" as your waypoint ID number (320-339), so the payload servo will activate one waypoint sooner than the waypoint coordinate that is programmed with the ID number of 320-339. Place this new waypoint into the route sequence of waypoints at the position you wish the payload servo to activate.

    3. If you wish to activate the servo more than once during the flight, you may now add up to 20 different waypoints using the above procedure.

    4. Set the payload servo reverse jumper for the desired direction of rotation.

    5. Turn on the autopilot and verify the range of servo rotation travel is correct for your application. Change servo horns, linkages, or servo mounting position if need be.


    Aerial Photography

    Many digital and film cameras can be easily adapted to take photographs automatically in flight. Digital cameras may be programmed to take up to 20 photographs during a flight. Cameras including Olympus D340, D360, D390 series have been successfully used with the AP4 autopilot.

    1. Mount your camera to the aircraft, preferrably near the center of gravity.

    2. Attach a servo to the top side of the camera, so that your servo horn will fully depress the shutter button with full rotation. A bracket or strap that slides around the camera is a good choice if you do not want to adhere the servo to the camera case.

    3. Turn on your camera and rotate the servo through its entire range of motion to verify that the shutter is fully depressed, and a photograph is stored into memory (may take a couple seconds)

    4. Plug this servo into the payload trigger socket of the autopilot (observing correct polarity).

    5. Program your gps to trigger the camera at the desired waypoint(s)(see 'Payload Programming' chapter above)


    Radio Failsafe Function

    In the unlikely event of loss of radio contact with your plane, the autopilot may be programmed to automatically fly your plane back to the airfield. The loss of a receiver signal on the autopilot on/off channel will automatically engage the autopilot. When no signal is present on the rudder and elevator receiver channels during autopilot engagement, the servo controls will default to standard center position.

    1. Check and adjust (if necessary) your plane's servo linkages to standard center by setting your transmitter controls to the center position, and then turning off the radio transmitter with the autopilot on. The rudder and elevator should not move more than a couple degrees.

    2. Program in the waypoint of the airfield into the gps and set to goto that waypoint before flying.


    Troubleshooting

    Autopilot does not operate servos

    1. Check that the receiver battery(s) are charged (>5.5v) and that all connectors are firmly inserted into the correct positions.

    Autopilot does not update servos (respond to gps)

    1. Check that an NMEA-0183 compatible gps is connected and that it is set to NMEA interface mode (consult your gps owner's manual), is turned on, and a sufficient number of satellites signals are available.

    Aircraft flies straight (instead of turning) when autopilot is switched on

    1. Check that an NMEA-0183 compatible gps is connected and that it is set to NMEA interface mode (consult your gps owner's manual), is turned on, and a sufficient number of satellites signals are available.

    2. Make sure that the waypoint the gps is going to is in a direction that should turn the plane.

    3. Check the rudder or elevator travel limit blue potentiometers to make sure they are not close to turned all the way counterclockwise. Turn them to 1/4 turn from counterclockwise if necessary.

    4. Check the rudder or elevator gain potentiometers to make sure they are not close to turned all the way counterclockwise. Turn them to 1/4 turn from counterclockwise if necessary.

    Aircraft circles or weaves when autopilot is switched on

    1. Check the rudder or elevator travel limit blue potentiometers to make sure they are not turned further clockwise than midpoint. Decrease 1/4 turn if necessary.

    2. Check the rudder or elevator gain blue potentiometers to make sure they are not turned further clockwise than midpoint. Decrease 1/4 turn if necessary.

    Aircraft does not turn quickly enough

    Use caution in increasing the travel limits as aircraft instability may result.

    1. Check the rudder or elevator travel limit blue potentiometers to make sure they are not close to turned all the way counterclockwise. Turn them to 1/4 turn from counterclockwise if necessary.

    3. Check the rudder or elevator gain potentiometers to make sure they are not close to turned all the way counterclockwise. Turn a few degrees further clockwise if necessary.