3rd phantom crashed when doing the same thing

[melihozbek]

Hi all,

Yesterday my phantom 2 crashed (but survived) and i had this crash with 2 other phantom 2 in the same way. I wonder if anybody has experienced a similar situation?

The video of the crash is here : http://www.youtube.com/watch?v=i3lA_uK5VjE

The pattern is like this:

First push the throttle up (to its maximum or not), phantom climbs to a high altitude (in this case it was around 130m). Look around, wander around and then push the throttle down a bit (not fully, just a bit to make it descent at a rate around 2-3 m/s, so it is about halfway down). While it descends (with no or very little wind up there) after a couple of meters, it starts to shake like crazy, the remote becomes unresponsive and phantom 2 crashes.

I lost one of them (fully loaded with gopro 3+, fpv) when exactly the same thing happened on a lake. Last week one of my friends' P2 crashed (by me) doing the same thing (thank god it survived). And now my new P2 did the same thing.

Has anybody had this type of crash while descending? Can it be a kind of firmware error?

The phantom 2 has the stock props, prop guards, avl58 (away from compass), iosd mini, h3-3d gimbal and all of them are connected to FPV hub (the previous ones had no FPV hub). It was at GPS mode (with 11 satellites), all the settings at their factory defaults, IOC is off and this was its 3rd flight (other two was without incidents but no high altitude/descends).

Is there a engine cut off mechanism if throttle is down for a specific time? But from the video you can see the engines did not stop during the crash.

Thanks

Melih

 

[EMCSQUAR]

It sounds like they're crashing because you're getting caught in prop wash. When descending try moving it in any direction while it's descending. Coming straight down especially a loaded Phantom between weight and P wash - they can't get pretty "wonky". Next time try moving it forward while descending - see if that improves your landings.

 

[ElGuano]

That's likely it. It would be helpful to know if this also happens when you come down at an angle as EMC suggests (down and forward or backwards with elevator, or to the sides with aileron). DJI limited the vertical descent speed in normal mode to 2 m/s, but it seems like there may be some instances when you still get caught in VRS.

 

[Uncle Meat]

Looks like rotor wash to me too. 2-3ms decent rate going straight down is just asking for trouble. As stated by EMCSQUAR you need to give it some forward or rearward stick in addition to reducing the throttle. I believe the latest DJI firmware reduces the speed of decent just to combat this type of issue. These flying machines DO NOT come straight down gracefully at all. If you want to drop down at a fast rate you need to be moving forward while descending to stay out of your own prop wash.

U.M.

 

[tom3holer]

Moving fwd especially on what looks likes a calm day is a big plus.

The other thing that stands out is the fact that with the heavy FPV setup you have and Prop Guards you are most likely way overweight.

I would remove the prop guards and fly without them.

Tom

 

[Rufus]

And with the latest firmware you can only descend at a speed of 2 meter/s.
That will garantee that too high descend speed is not your problem.

 

[pault]

Also have to be careful which direction you go whilst descending as it will not improve matters if you fly with the wind as you will still be in your own prop wash. The best way I have found is to flip into ATTI for a few moments to show which way the wind is blowing (it may be different aloft) and then move into (against) the wind as you come down. Using this method it is possible to safely descend quite fast. A lot of people also like coming down in a spiral but personally I avoid that as for some of the circle you will again be in your prop wash.

 

[ianwood]

And with the latest firmware you can only descend at a speed of 2 meter/s.
That will garantee that too high descend speed is not your problem.

It doesn't guarantee anything. VRS can happen as low as 1m/s depending on conditions. The best way to stop VRS from happening is to be able to detect the onset and take corrective action.

 

[QYV]

that totally looks like a vortex ring state, sounds like one too you could tell it was trying.
It's also the general consensus around here that prop guards make a vrs more likely. unless there's a high potential for bonking into things where you're flying I would also recommend you fly without them.

If you've never upgraded your firmware, your max descent rate is much higher than 2-3 m/s and is more likely to experience the vrs. The others suggesting to always have lateral movement and not descend straight down are absolutely correct.

If you don't understand exactly what a VRS is, highly recommend you research it online but basically this is it: have you ever stood under your Phantom and felt the air it's moving? if you descend straight down you're descending into that disturbed air which is also moving down at a high rate, the propellers can't grab "new" air to generate lift, therefore it just falls. if it happens you can usually recover by slamming the right stick in any direction to try to get some lateral movement and get into good air. not always of course nothing is for certain but just working the throttle (left stick up/down) won't do anything.

 

[mikouk]

This is exactly the same thing mine did. Except mine wasn't that high. Hopefully that explains it and i can take the same advice. It certainly was a scary moment!

 

[The Editor]

Agree with comments above - In addition get rid of the prop guards.

They destabilize the aircraft and do no favours in respect of maintaining control or weight distribution.

 

[melihozbek]

HI,

Thanks for the helpful tips, Now things make sense. This is a new field for me, and i think i didn't take it as seriously as I should.

regards,

Melih

 

[ladykate]

As the doctor's advice goes when the patient asked what to do with his wrist that hurts every time he bends it back - "Stop bending it back." In this case, stop descending into your wash.

Destabilization by descending into your own wash will happen - listen to the motors and watch - the platform will start to wobble and the motors will start complaining as the NAZA tries to compensate. Steer away from the position using pitch or roll and don't come down as fast. Besides, it looks cool when it flies down into the landing field at an angle - looks like you are really flying it - which you are.

FWIW, with the new settings you can still get it to go unstable when coming down. Was flying last weekend and got it to bounce around a lot - new machine and latest firmware.

 

[melihozbek]

I also have groundstation and bluetooth datalink, but it is not installed yet. The general opinion is prop guards are already excessive weight for the current configuration (AVL58 + iosd mini).. Should I detach FPV when I want to use BT datalink?

I'll try the 'cooler landing style'

 

[Fdnyfish]

So because this gentlemans P2 is overweight, does this mean that failsafe may result in the same way?

 

[Cygan]

Had the same question a while ago. Look it up. VR.

 

[Uncle Meat]

So because this gentlemans P2 is overweight, does this mean that failsafe may result in the same way?

I wouldn't think so. The quad-rotor will automatically land if the fail-safe mode is active, or return home if in GPS mode. Either way as long as there's sufficient battery power left it descends at a pretty slow and steady rate as dictated by the firmware in the Naza. I've yet to see, read, or hear about a Phantom that went into VRS on its own while in fail-safe mode.

Had the same question a while ago. Look it up. VR.

Wow! Very informative post. 5 stars! Will read again. Thanks. :roll:

U.M.