Pixhawk Hex Take Off Stability problems

Posted by Peter Arnold on March 2, 2017 at 12:24am

Hi.

I am having major stability problems on takeoff with my Pixhawk controlled Tarot 810 Hex. If I try and take off smoothly and slowly it starts wobbling and will usually flip onto its side. If I get it to leap into the air by applying the throttle quickly it will stabilize in the air and fly smoothly.  I have a small Pixhawk controlled Quad which will take off nice and stable so I can’t work out what the problem with the Hex is.

My kit is as follows.

Tarot 810 sport.

Pixhawk with latest firmware

KDE 3510XF 475 motors.

1555 CF Props

Hobbywing XRotor pro 40A ESC

10,000 mAh 6S batteries x 2

The ESCs are calibrated and start rotating at the same time. The props are balanced. There is nothing loose on the frame. The motors are all lined up correctly and rotate in the correct direction.

I attach the log of my last take off attempt which ended up in a flip. Also attached is a snapshot of my PID settings.

The only thing I can think of is a compatibility issue with the ESCs / Motors / Props???

If anyone can help it would be appreciated.

Thanks

Peter

Tarot PID Settings.pdf

14.BIN

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Replies

  • Fernando Vegas May 9, 2017 at 10:52am

    I have the same frame with 4016 380Kv motors. 16 Amp Bat. Pixhawk. 

    Some issues :  

    RC_FEEL_RP = 50 is overpower, try 45-48

    PID: After auto tuning the multi is very responsive, lower P value will make it smoother. 

    Take off: "smoothly and slowly", My guess : Perhaps you'd try to take off too slowly and the copter haven't enough power.

    Check the take off in this video (8:50 min) . It's pretty similar to my takeoff. 

    https://www.youtube.com/watch?v=Z0mueJWRXJA

  • Arbutus March 29, 2017 at 4:37pm

    Any updates Peter?

    I have an 1100 hex to maiden in the next few days - 

    8Kg (+3kg payload)

    5008-330kv

    18x5 props 3.3Kg max 

    50A ESCs

    6S2P 20,000mAh Graphene

    I am very interested in your PID setup, particularly the solution to the takeoff wobble you had mentioned earlier.

     

  • Clifton Hipsher March 3, 2017 at 4:04am



    Peter Arnold said:

    At 8 kgs the calculator gives 

    Hover Thrust = 11,220 g 

    Maximum Thrust = 21,120 g 

    Peak Efficiency = 12.857 g/W

    Being 2 Kgs lighter would make it a bit more sensitive?

    Definitely.

  • Peter Arnold March 2, 2017 at 9:24pm

    At 8 kgs the calculator gives 

    Hover Thrust = 11,220 g 

    Maximum Thrust = 21,120 g 

    Peak Efficiency = 12.857 g/W

    Being 2 Kgs lighter would make it a bit more sensitive?

  • Peter Arnold March 2, 2017 at 7:58pm

    Hi Justin.

    Good question. The present weight is 6 Kg and but with the camera gear it will be about 8 kgs. Using the KDE calculator and 8 kgs they recommend the KDE 3510XF 475 motors. which is what I have. At the present weight of 6 kgs it is a bit over powered.

    At 8kgs the calculator gives 

  • Clifton Hipsher March 2, 2017 at 4:13pm



    Peter Arnold said:

    Thanks for the further information!

    I had RC_FEEL_RP set at 50 just as a starting point and will try and do some in flight tuning.Maybe work my way up towards 11 bit by bit.

    However I'm a bit confused about the Inflight Tuning. It says to Set the CH6 Opt to “Rate Roll/Pitch kP” and do the tuning in Stabilised mode.This I assume, will adjust the main Pitch Roll channels and the Stabilised P values won't change? Do you then inflight tune the Stabilised P values.

    Once you get Roll and Pitch tuned I seriously doubt you will have to tune the Stabilize PIDs

     

  • Justin March 2, 2017 at 4:07pm
    With the two 10,000mah batteries.
  • Justin March 2, 2017 at 4:05pm
    What's your thrust to weight ratio? First have to determine if you have an over or underpowered quad.
  • Peter Arnold March 2, 2017 at 1:21pm

    Thanks for the further information!

    I had RC_FEEL_RP set at 50 just as a starting point and will try and do some in flight tuning.Maybe work my way up towards 11 bit by bit.

    However I'm a bit confused about the Inflight Tuning. It says to Set the CH6 Opt to “Rate Roll/Pitch kP” and do the tuning in Stabilised mode.This I assume, will adjust the main Pitch Roll channels and the Stabilised P values won't change? Do you then inflight tune the Stabilised P values.

     

  • Clifton Hipsher March 2, 2017 at 11:41am

    Some other things that can jump up and bite you:

    1.  RC_FEEL_RP, particularly when the aircraft is overpowered (hovers below 50% throttle).

    2.  Autotune.  I prefer using In Flight Tuning.  I ran AutoTune on a quad that was flying fine on the defaults.  AutoTune made one hell of a mess.  I had to wipe the FC and start over...

    InFlight tuning of Roll and Pitch — Copter documentation
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