Is there a mathematical solution for preventing fly-aways?

My understanding is that the following is what causes them:

- Accel z goes negative due to ship vibration versus an actual drop in altitude
- The ship corrects by adding power
- The added power causes a larger vibration-induced negative z
- The ship corrects the pseudo altitude drop by adding more power
- A fly away occurs

My understanding of mathematical solutions are:

- A filtered or weighted z only diminishes (does not solve) the effect.

Has anyone tried a "significant z", z / s, where s is the moving average of the variation of z?
- when the IMU isn't vibrating, s is low so the magnitude of z / s is high
   ... z is significant
   ... z can be trusted for use in altitude control
- when the IMU is vibrating,   s is high so the magnitude of z / s is low
   ... z / s has less effect
   ... and will not caused a flyaway

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Thanks for the clarification on the SF11/C. I might have to try one.

How close are you to either getting Pixhawk code to weight the inputs based on elevation or integrating your own baro into your chip to do the same? It sounds like a small fix.

Seriously?

@Laser Developer

considering the cost of the laser, I rather use it for avoidance system.I would appreciate very much if you can educate me on the laser usage in avoidance,

As for atitude issue, correct me if I'm wrong, I believe the current setup is OK (eg. dji phantom 3 is very stable even in 25+ wind). 

FPV? Congrats Cala.

Jim and I sponsored a racer (ship optimization for speed and response) in exchange for him teaching us FPV. Unfortunately after a great start, i got side tracked winning the multi-hull trans-Atlantic race so Jim is way ahead of me. Yes, holding altitude well would really help one learn FPV. Great idea.

Go Cala! 

After Darwin's evolution theory negation, this is a new one! Of course gravity exists, it is a real effect you experience permanently and that is mathematically perfectly and precisely defined. What you are really saying is that the classical explanation about what is gravity may not be what we think, but the "how" exists. 

I sit here and read all these suggestions and "problems" that i personally never experience. I am yet to see a fly-away for myself. Hundreds of hours of flight time from 3.0 to 3.3 ... 

How common are these issues and is it fair to bunch them all into one issue " FLY AWAYS" 

@Forrest - The Pixhawk code already does some of this depending on which mode you're running in. If you need more details I can get our dev to chat to you.

The hardware version is part of a bigger project to get UAVCAN connectivity to meet the requirements for high reliability commercial drones. I've got all the boards and parts waiting to take shape but at the moment it's not our highest priority project. I might get to it in the next few months.

@YT - avoidance is more complicated than altitude control and we have the SF40 to do this job. There is a description of the operation in the manual but Pixhawk integration is not yet available.

Altitude stability has been discussed throughout this thread so I won't go into any more detail other than to say that it is not quite as simple as it appears to be ;).

A Fly-Away is like love. Once you experience it you know it. Unlike love, which i hope everyone experiences, you really don't want to experience a Fly-Away.

My solution was to build stiff ships, so i never experienced it, until i bought a Pixhawk with faulty IMUs (there was a bad batch).

Thus while the cause can vary (mostly because of excessive ship vibrations), the internal process appears to be same in every case. The ship in using accel-z for altitude control gets into a loop that can cause your ship to suddenly and at full speed rocket into the air before you can switch out of the alt-hold subroutine. It flies to a height where you can no longer discern ship attitude. In most cases, the ship is lost due to a crash from 100 meters or permanently lost in the nearby woods, or lake, or .... can't see it coming, ends in a crash ... it does sound like young love :-)

@Tony,

every time you fly at high altitude, side wind can make your drone to fly-away (100+ drone fly-away syndrome cases reported recently).

Low mass drone is not fit to fly at higher altitude on windy days.

Flying a kite first to calculate wind speed and direction is a nice technology to get your drone protected against fly-away.

you sound like you know what you are doing. let's chat

So you mean when there is noo GPS signal ? If so why would you fly so high (and you should not ) without GPS signal.   If you do have GPS ; that is your reference point and the drone IF capable (power) will fight the wind. If your drone has no power you cannot fight the wind no matter what you do in SW because its a hardware issue.. I still do not see the problem here. Each of your fly aways are unique in a problem and there cant be a one solution for all type of thing 

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