landing altitude control

There is a simple control technique to get good altitude control during autonomous landings. Turn off the throttle and follow a glide path defined by 2 waypoints. The first point is the approach point, and should be about 10 meters above the beginning of the runway. The second point defines the glide path, and should have a negative height, and be unreachable.

Whenever the plane is above the desired landing glide path, the pitch altitude control should be programmed to engage. Whenever the plane is below the desired glide path, altitude control should simply maintain level pitch, that will keep the unpowered plane from stalling.

If the plane is landing against the wind, it will land close to the first waypoint. If it is landing with the wind, it will land where the glide path intersects the ground.

The above pair of tracks were recorded during 8 autonomous flights of an EasyStar that I made today. Waypoint7 is the approach point, and waypoint8 defines the glide path. The two landings were within 7 meters of each other, and close to the intended landing point.

Best regards,

Bill Premerlani

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  • T3
    Hi ionut,

    Thanks for reminding me about the links, I have updated them.

    I recommend the 406 simply because it works well and I have a certain fondness for it. The latest version of MatrixPilot in the code repository currently offers dead-reckoning, which leverages the GPS information up to a 40 Hz update rate, so the underlying reporting rate of the GPS is not all that relevant. I personally do not have any data on the MediaTek, but we have some recent data on the uBlox that shows there is filtering going on internally, such that it takes the velocities reported by the uBlox to take 2 seconds to reflect a step change in speed.

    Regarding the V tail, I am not sure. I suggest that you repost your question on that subject to the uavdevboard users group.

    Best regards,
  • Bill,
    I see the link on DIYDrones to UAV Board is rather old.Also why do you recommend that 406 gps and not this one:
    which is cheaper?Do you think this one will fit?

    Also my plane has V tail.Does UAV deal with aelerons and V-mix?
  • Bill,
    I have but I'm confused of the multiple version of Ardupilot+shields.I want something simple,not to experiment too much.One bord+one software.
  • T3

    I almost forgot to ask you....have you considered getting an ArduPilot?

  • T3
    Hi ionut,

    If you are asking for a comparison between MatrixPilot and Paparazzi, I cannot help you, I have never used Paparazzi. Perhaps someone who has used both can comment.

    MatrixPilot is a relative newcomer on the scene, but we have made great strides in achieving high performance. If you have some specific questions about how it works, I would be happy to answer them. I am not sure what drift issues you are referring to, but MatrixPilot does not have any drift issues. Also, as you can see from the flight track, the turns are very smooth.

    In its present form, it is very accurate and repeatible. Autonomous landings are routine.

    MatrixPilot offers a wind estimation algorithm. For example, you might want to take a look at my reply to a recent discussion of the subject.

    Best regards,
  • Hi Bill,
    I'm confused.I planned to buy eaither your MatrixPilot or european Paparazzi.As I saw paparazzi deals better with curbs because it uses IR sensor and not having drift issues.
  • If you have an IR beacon and hold it in the "centre" of the frame of your UAV-mounted camera, whilst it won't give you any slope indication, it will give you an exact aiming point in the manner of the "looming" effect where everything you won't hit doesn't remain stationary in the viewfinder/frame. You might need to add some angle-of-attack compensation to the camera or the definition of the centre of your frame for control purposes, or you could just use the vertical centreline and make it a nav homing beacon if the attitude compensation proves too difficult.
  • Perfect landings are nice but make it does it to the webcam on a 15ft lead xD
  • Keeping the dot at a fixed location on the camera will allow you to surpass GPS (and ignore it) and gets rid of any need for an ultrasonic sensor. You'd land PERFECTLY and exactly in the right spot. Sounds like something to try!
  • @PAS
    Take off the IR filter then get a visible light filter off eBay. That is what I have done for my 3D scanner. FEZ mini looks like a valid "copy n paste" option for a payload version too.
    As for guidance you guys have lost me. Sounds nice though xD
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