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

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Hi,

Seems you do not have good accelerometer calibration. I have same issue when move the copter to different location - 20-30 km or more from the previous calibration site.

You should first calibrate the compass and then accelerometer in all positions - top, left/right side, nose up/down and copter back up.

Then put the copter on the ground for flight, and calibrate level immediately before the flight.

All should be OK.

Have you managed to complete Autotune?  This is a common problem with the first flight.

If you are unable to achieve stable flight in Althold, required for Autotune, then try increasing the "stabilize P"  value by a small bit, or better configure the tuning knob on ch6 to adjust this value, achieve stable Althold, only then perform Autotune.  I think this will help.

You're just staying on the ground too long.  Flybarless helis do the exact same thing.

The problem stems from the fact that as soon as you arm the motors, the flight controller is trying to keep the airframe level.

A flybarless heli gyro does this by tilting the main rotor disk, and a rookie FBL heli pilot's first mistake is trying to level the rotor disk before he takes off,  Because the airframe is still on the ground the gyro tries harder to level the airframe and the heli tips over.  BTDT.  

This is situation is exacerbated by a multirotor. In both aircraft, the fix is to get into the air "smartly".

Thanks for the replies! 

I'm confident the accelerometer calibration is OK and when it is in the air it flies well and is very stable. I have done a auto tune but later wound the P back hoping it would fix the take off problem. 

Clifton may have answer by not staying on the ground so long. I was expecting my hex to fly like my small quad

Are there any other larger copter pilots out there that can give some advice on take off techniques? 

Peter,

I have an 850mm quad with Pixhawk.  Two things come to mind.  One, I agree with Clifton.  "pilot's first mistake is trying to level the rotor disk before he takes off,  Because the airframe is still on the ground the gyro tries harder to level the airframe and the heli tips over."  Second, take off in either althold or stabile modes to avoid the "flip over death mode".  I will not "slowly" apply throttle for take off.  Quick throttle (not "full" throttle) just to get her off the ground quickly....just a few feet up.

Marty

I have a heavy Y6, 7.5KG.  I had major problems taking off for my first flight.  The tendency to flip or do some other unwanted action was potentially very dangerous.  I needed to raise stabilize P just to get off the ground.  Once I completed Autotune Stabilize P went up around 9.5, after that the flipping tendency was over.  Now I typically take off in loiter mode, and that's very stable, fast or slow, no problem.  My feeling is that you need to return Stabilize P back to the autotune value or perhaps higher.

How is your loiter performance? 

Harry

After the autotune I ended up with the following

Roll

  • Stabilized         11.28315
  • P          0.3476464
  • I           0.3476464
  • D          0.0163874
  • IMAX   200

Pitch

  • Stabilized         11.84731
  • P          0.3033321
  • I           0.3033321
  • D          0.01511602
  • IMAX   200

 

Yaw

  • Stabilized         6.282879
  • P          0.9271545
  • I           0.09271545
  • D          0.000
  • IMAX   100

I was still getting the Take off wobble issue so I reset the Stabilised Roll and Pitch to 4.6 and Yaw to 4.0 hoping it would help.I usually use stabilise for take off but will try Loiter. I sustained a bit damage on my last episode so it will be a few days before I can get back in the air.

Thanks for the advise, very helpful!

Hard to tell if the values are to high (creating oscillation) or to low (inadequate reaction from the controller).

When I was getting off the ground I adjusted stabilized roll and pitch no more than 1.0 for each attempt.  Try upping the values to 8 or 9.  Still down from 11, but I expect if this is the cure you will know right away.

In my case my Y6 is very sensitive in stabilize mode.  Its a little shocking at first.  So I try to focus on loiter mode, as it is a GPS guided condition, no fear at all.  I should mention, from other posts I understand that loiter should not be initially attempted until Althold and stabilize modes works, <very> well.  The bad possibilities are real, and you can't take risks with a heavy beast.

I am embarrassed to admit that I was cut on two occasions before I successfully tuned the PID settings.  I now have great respect for the power and control.

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...

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.

 

What's your thrust to weight ratio? First have to determine if you have an over or underpowered quad.
With the two 10,000mah batteries.

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