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Old 09-12-2015, 02:37 AM   #1 (permalink)
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Join Date: Sep 2015
Default S1000 crash - exponential drift

Dear All, today I had a big crash with my DJI S1000. Could you help me to understand what it was wrong?
The crash was due to a instable situation where i was unable to let it land at home.
The S1000 went up normally (vertically), then it was unable to hold a position. it started to drift from its position and, leaving it without commands on sticks, its speed increases esponentially. Each time, I had to correct this exponential drift to let it return close to me. The drift direction was never the same. 2 times it started to spin around me in a circle with increasing diameter, tring to correct itself (with gps i suppose). Yesterday, in this situation, i was able to put it in hovering over me by playing on the sticks, and i successful landed. Today I was not so lucky and i had the crash, but the problem was the same, even if today i changed some parameters.

This is my setup:
-DJI S1000
-DJI Lightbridge (to receive telemetery and video and to send commands)
-GOPRO camera without gimbal
-A2 flight controller

Configuration details:
-I calibrated the compass one month ago
-I never sow this copter flying stable
-These are the first tests with the S1000, my experiences are with phantom2 and ardupilot self built octocopter.
-yesterday the gains were setted to 100% but i read on the dji manual that the gains on A2 used on S1000 shall be setted as follow: roll 120% pitch 120% yaw 120%
-today i moved the gains as recommended on the DJI manual (120%)
-yesterday the IMU position, in A2 configuration, was in the center of gravity, but the truth is that the IMU real position in S1000 is 10cm more backward than the center of gravity
-Today i configured, on the A2 configuration software, the position of the IMU backward, to correspond to the real position of the IMU (around 10 cm backward)
-Yesterday the position of the GPS, in A2 configuration, was in the center of gravity, but the truth is that the F
GPS real position in S1000 is around 10cm higher than the center of gravity.
-Today i configured, on the A2 configuration software, the position of the GPS, to be 10 centimeters higher than the center of gravity (in order to let it correspond to the real position of the GPS).

Details about the flight:
-i was flying in GPS mode
-on the telemetry I had 11 satellites even during the flight.
-the vibrations seemed low, because the gopro camera fixed on the top of the copter recorded a good video, just a little bit a jellow effect but this is normal because there was no gimbal.

Any help to understand will be appreciated.
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Old 09-12-2015, 06:02 PM   #2 (permalink)
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Sorry about your crash man. It's really painful when a big bird like that bites the dust.
It's always good to start with the basics in trying to trouble shoot anything, but I'm going to assume that since you're flying a big bird like this, you have all the obvious stuff covered, like a reasonably centered CG, no mixed up props ( a bird like yours can still fly with a mixed up pair of props - just not very well), etc. I saw that you posted that it has never flown right. Does that include flying it without the GPS? When I build a new bird, I always test it first with no GPS (or even self leveling) turned on. This helps expose any nasty problems that might be lurking under the surface.
Summing up: Get the bird back together, then test fly it in manual mode on a very calm day. Best of luck!
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