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Precision Landing Parameter for fixed wing UAV

arduplane
pixhawk2

(Zul ) #1

Hey guys, I am working on to improve autonomous landing for my fixed wing UAV since the landing is always overshoot. Based on my reading, I found out that I need to control the parameter such as LAND_FLARE_ALT, LAND_PITCH_CD, etc. However, it is hard for me to find the exact value for those parameters. Can you guys help me, please??


(Nathan E) #2

You will most likely need to post a log. It would be best if you did glides at different angles of attack and had an airspeed sensor so we can analyze your descents.

I found the TECS_LAND_SINK to be the most useful in preventing overshoot. In your case, you will want to lower it. That will cause the flare point position to move further away from your landing zone.


(jstarch) #3

…“In your case, you will want to lower it.”

Does that mean make the
“TECS_LAND_SINK” a larger number or a smaller number?


(Zul ) #4

Dear Naterater, can you share the idea in parameter code and the value for precision landing if capable, thank you.


(Nathan E) #5

Smaller value, my apologies.

I also cannot post parameters as they vary with each type of aircraft.


(jstarch) #6

Nathan … for clarity,
Will not a smaller value for the ‘tecs_land_sink’ parameter cause the fixed wing to further overshoot the ‘land’ waypoint?
I think I am a bit confused over this point as I am having the same issue getting touchdown at the waypoint (rather it is consistently overshooting/long)


(Nathan E) #7

The documentation on how this works is rather unclear and somewhat unintuitive. The system “back-calculates” the flare position using TECS_LAND_SINK. By making the value smaller, the flare point moves further away from the touchdown point because the estimated flare angle is much smaller due to the reduced sink rate.

I think some of the answers are here: https://github.com/ArduPilot/ardupilot/issues/9934#issuecomment-443551987


(jstarch) #8

Nathan,

okay - thanks.

I will read that.

I guess since I was constantly overshooting I figured I needed to raise that number (to get a faster ‘sink’ rate/steeper slope).

In raising that number I just keep making my overshoot worse…


(jstarch) #9

I already have the TECS_LAND_SINK set at .2 (point two).
That seems so shallow that the plane will never ‘sink’ or descend
this is confusing. You explained it well with saying it will move the flare point further away; however, if the thing (fixed wind) has such a small ‘sink’ rate I will need a 1/4 mile or further for an approach and land yes?


(Nathan E) #10

The TECS_LAND_SINK is only valid for the flare. The first part of the approach is controlled by the altitude of the waypoint just before the land waypoint. It is often shallow (~6 degrees or less for my plane to glide with very little/no throttle)

Let’s say your plane lands at 10m/s. If the flare altitude is 2m and the TECS_LAND_SINK is .2m/s, then the flare should happen 10s before the land waypoint. That flare should be 100m away from the land waypoint because the plane travels 10m/s. I can promise you that your plane will not make it 100m on no throttle with only 2m of altitude clearance.

This is an extreme just to paint the picture, but that should make some sense. Maybe your approach isn’t long enough allowing a good descent to the flare point. Unfortunately Mission Planner does not know how to calculate a flare and the resulting glide slope to the flare point. Only ardupilot knows how to do that.


(jstarch) #11

Excellent point(s) all of them…

I will make the changes according and test. Looking forward to it.
… the only problem (I can’t get back in the air soon enough) : )