The Ardupilot firmware project is the best initiative I have seen in years.
My problem is not the firmware but my understanding of the tuning. Already for months, and with several crashes, I’m trying to get my Mini Talon stable. The CG is tuned correctly and in manual no problems.
I tried to use parameter files of other users, and used Auto tuning.
On the DIYDRONE forum I also posted related questions but nobody was answering.
But it remains that the altitude is very instable, especially during decents at approach and auto landing.
Normal flight the altitude is stable.
When the approach starts, the plane is at moment at an altitude of 4meters .Normally the plane could just land without throttle.
You clearly see the Pitch is following the NavPitch with a phase_delay of almost 90 degree, you also see a heavy Pitch swing with peak2peak amplitude of 50.
But also the throttle is engaged for 70%, which results in height and speed increase and an overshoot of the “runway”
When the Flare is started, no more throttle, and the Pitch oscillation is damped out.
What I would like to understand what is wrong, I expect something in the TECS tuning ?
I tried to change the following parameters:
TECS_SPDWEIGHT 1.2
TECS_PTCH_DAMP 0.4
TECS_LAND_SRC 0.1
TECS_LAND_TDAMP 0.6 m/s/m
TECS_LAND_THR 10%
But non of the changes gave any improvement.
Plane:
Mini Talon AUW 1200g, 3S 2200mAh battery
Pixhawk, ArduPlane V3.6.0
THANKS a lot for answering !!! I became more and more fustrated with this problem.
I assume you mean the sink limits ?:
TECS_SINK_MAX 5 m/s
TECS_LAND_SINK 0.25 m/s
Do you know where in the log file I can find the vertical airspeed ?
In that case I can see if the controller act on the limit.
What I also found is that the instability becomes more severe when the total weight of the plane increases (by adding lead in the CG point), even with increased throttle setting the vertical stability is worse. In itself this is not strange but I don’t know on which knob to turn to make it more stable. I increase the weight as I intend to add more batteries for an endurance flight.
Yeah that’s sorta what I was thinking. The other thing is the TECS seems to not be tremendously tight about airspeed or Alt. I use the speedweight term to tighten the airspeed control at the expense of altitude. Another thing is that is you run into ARSPD_FBW_MAX then the vehicle seems to pitch up. I’m not sure about your plane, but some planes are hard to get down in this manner without flaps.
I also have a mini talon.Its a very aggresive plane.
it likes speed and its not easy to handle easy landings.
i have pitch oscilations during cruise.TECS_SPD_WEIGHT=2.
i think you must find the tricky number for cruise speed depending the AUW.
@kostaslbc
Verrry good to hear I’m not the only one. Indeed (Auto) landing is tricky or you neeed a lot of space.
I also played around with TECS_SPD_WEIGHT in a range from 0.5 … 1.2.
What is your AUW ? mine is now around 1300g but has to go up to 1600g
my AUW is 2280 grams !
i did not make any autotune yet.in my last talon(with aututune) i didnt see any important changes during flight (AUTO,CRIUSE).I attached you my param file. TALONAFTERCRASH.param (11.0 KB)
I had a look in my flight log’s: my airspeed was never over 14 m/s during these instable moments.
Anyhow today I did a small testflight with some adapted parameters:
TECS_THR_DAMP 0.5 --> 0.7 gave perhaps biggest improvement
TECS_SPDWEIGHT 1.0 —> 0.8 Not sure
AIRSPD_FBW_MAX 14 --> 18 No influence as speed was always lower (for security increased)
The result was very little trottle engagement during final approach, and hence no runway overshoot and precise Auto_landing, also less altitude overshoot with same flightplan as previous flights.
This all with a AUW of 1300g, now I’m going to increase this and observe TECS stability.