DJI F550 Crash - Free fall

A

AlexVen

Member
Hi Guys,

I have encountered a strange phenomenon with my F550 which I hope you can help me with.

Setup:
DJI F550
Naza
2 X 3C 3300mah (turnigy nanotech)
Graupner 10x5
Stock DJI motor and ESC (30amp)
Havafilm gimbal
Sony Nex5

Weight: 2.7kg
Normal flight time with DJI 10 inch prop: 7-8 minutes.

Up until today I have been flying with the stock DJI 10 inch prop which worked well with the heavy weight and provided a fairly stable flight. Today I installed the Graupner 10x5 props on the recommendation of many in this forum and after around 3-4 minutes of flight time it decided to free fall from a hover and around 20 metres in height, albeit a slightly wobbly free fall! I tried to give it a large amount of throttle but this didn't help at all. It was if there was too much weight and the inertia was too great for the Graupner props and the little DJI motors to stop the descent. Of course I hit the very hard concrete. Fortunately, the gimbal took most of the impact. Before the crash I noticed that it was very sluggish to throttle responses. I would almost have to predict my vertical responses 2-3 seconds in advance. Pitch and Yaw were fine.

Next flight with the gimbal straightened out I increased the vertical gain to 190 from 160 and the other gains to the same amount and tried again. This improved the responsiveness a little, however, the F550 was still very difficult to control vertically. I continued to fly and did not notice the low battery led light blinking away. Whilst sitting in a nice hover the F550 again decided to go in to a death descent from around 20 metres, again! Even though the battery was low I don't believe the crash was due to this. This time I tried to fly forward thinking that I was in the prop wash, however, this didn't help. Below is a video of the crash. I did not believe I required washers under the Graupners as the nut was VERY tight on top of the prop with absolutely no slipping.

I took the damaged and irreparable gimbal off and tried to fly it "naked", exhausting a whole two batteries; it flew really, really well!

I have now increased the vertical gain to around 250 and will try it out when the replacement gimbal arrives. Obviously I don't want to encounter the same problem again. Can anyone explain what I, the F550 or someone else did wrong??? Do you think increasing the vertical gain to 250 will solve my problem?

Thanks in advance for any advice,

Alex V

 
Last edited by a moderator:

L

Langdale

Member
Have you put some tape over the left side of the Naza? It is a known fault that sunlight hitting the Naza will cause a suddenly loss of altitude. When you took the gimbal off and flown, you might not have been exposing the left side to the sun.
Peter
 

A

AlexVen

Member
Hi Langdale,

Thanks for your suggestion. I will definitely try this next time as the F550 would have had it's left side facing the sun when the free fall occurred. Saying that, the naza unit was neatly covered by cables and cable sleeves. There wouldn't have been much exposure to the light.

Alex V
 
Last edited by a moderator:


T

tugboat

Member
I don't think increasing the gain will save you....
In your video it does not sound like the motors cut out at all, if you removed the gimble and she flew fine it would seem to be a issue with the gimble wiring, maybe...
But if you have not added the black tape to the side of the naza then you must... it is a known issue with these naza fc's, some will put tape on both sides (I did) then when I moved the fc to the top deck on my disco I had to put even more tape on the top of the fc as she did the classic up and down due to the sunlight's effect (instantly cured).
Can you post a couple of pic's of your hexa's layout?? it would be helpful to see...
Sorry about your crash, it was painful to watch!!
 

B

bruce365

Null
Hi AlexVen, In the Naza assistant check your Voltage settings. I also have the F550 with all standard except I installed graupner props. To overcome the problem with the thinner hub I simply chamfered the internal aluminium spinner thread, that will give you enough to lock the props tight. The reason your props are tight at the moment is because the spinners are pressing against the bold printing on the prop hub, once that wears off your props will be loose. I placed my fc rx tight against the left side of the Naza to stop the sunlight. The Graupner props have a much smaller chord than the DJI props, therefore less surface area to carry your weight of 2.7kg which is above the recommended maximum. When changing to Graupner props you should have also changed your battery to a 4S (higher voltage gives the motors a bit more punch). My F550 weighs 2.450kg and there is a considerable difference in performance and response when I take the landing gear / gimbal and camera off, its a completely different experience. I had an experience where my second level Low Voltage Cut off was set too high and as I was flying across the field on return the F550 suddenly dropped and landed fairly hard, I increased throttle but this made no difference as the Naza simply landed. In my case I was only about 20ft above a grassy field and there was no damage to the landing gear but never the less the landing was very rapid and on concrete my landing gear would have sustained some damage. No Idea if any of this would be helpful to you but maybe. regards - bruce
 

You must log in or register to reply here.
Top