[Rickolas]

Morning all.

My first flight a few weeks ago went great, took off no problem, stabilized no issue and flew fine.

Yesterday however, a different story.  When trying to take off, its immediately pitching rearwards and flips on takeoff. It's had me frustrated as i could not get it to fly.  The only thing that has changed in the config since, is the addition of a GPS receiver, and OpLink enabled.  For the purposes of testing last night, i turned both of these off, but still have issues. 

I have also tried calibrating Mag, Gyro, Board Level, and Accelerometer.   None seem to make a difference.  What is odd is the flight data tab is showing the aircraft level in the top level indicator, but the pic of the drone shows as if it's pitched forward 90 degrees, so i wonder if this has something to do with it.

My flight modes remain unchanged apart from mode 3 is now return to base, except i have not even got a chance to select this in flight yet. Attitude estimation is set to GPS Navigation (INS13).

My setup consists of:
Revo FC
Chaos 25A Bheli-S ESC x4
Chaos 2205 2300kv Motors
Oplink
Ublox 7M GPS
Flysky X6B Receiver

Short of wiping the whole thing and starting from scratch, is there anything i can specifically look for to resolve the issue?

[TheOtherCliff]

What did you unplug and think you plugged back in in the same place (ESCs)?

Did you remove/reinstall the FC (in a different direction)?

When you have a working setup, save it (File->Export...) "just in case".

[Rickolas]

What did you unplug and think you plugged back in in the same place (ESCs)?

Did you remove/reinstall the FC (in a different direction)?

When you have a working setup, save it (File->Export...) "just in case".

Nothing has been moved. Oplink and GPS were added with the FC still mounted to the frame. ESC's have been untouched

[TheOtherCliff]

It seems that something has changed.  Did you remove and reinstall props?

Or motor wiring (3 wires from ESC to motor)?

Is a prop badly out of balance?

[Rickolas]

It seems that something has changed.  Did you remove and reinstall props?

Or motor wiring (3 wires from ESC to motor)?

Is a prop badly out of balance?

I always remove props after a flight, but have not touched anything at all like motor connections or anything related to ESC's.   I have enabled the motors to spin when armed, and all 4 move in the correct direction. When armed and giving it a little throttle the South East motor stays the same rate as armed while the others spin faster. The only thing that changes the speed of the SE motor is pointing the Pitch/Roll stick to the 10 o'clock position, but even then when trying to take off, the copter still pitches rearward and if you centre the right stick it flips over and heads for the ground.

I think i'm going to wipe and start from scratch again.

[TheOtherCliff]

Slow spin up is normal.  'I' term windup...

If you put props back on the wrong motor it would flip.   CW vs. CCW   I've done it. 

Make sure you have Stabilization->ZeroTheIntegral... set to ENABLED.  Always take off immediately after the motors start to spin.  Immediately jump off the ground to knee high rather than slowly increasing motors.  Leave the control sticks in the middle till in the air.  Do not try to help steer it when touching the ground.

Dangerous:  For small quads and strong hands, you can switch to Rate mode, hold it in hand firmly from below, add the smallest amount of power possible while being ready that if something is backwards, it will use full power to try to flip over.  If it doesn't try to twist out of your hand, things are right, if it tries to twist hard, something is backwards.

[TheOtherCliff]

From that other thread, you added GPS and now it flips.

I had thought you changed everything back.  If you still have AttiEstAlog set to INS13 you must have your GPS/mag mounted correctly (level and with arrow on GPS case pointing forward) because the mag is used for leveling too, and more importantly, if you have I2C aux mag, you absolutely must have aux mag orientation (in Attitude->Magnetomenters) set to 0,180,0 or 180,0,180 (they have the same effect) because the mag chip inside is mounted upside down and backwards.

https://librepilot.atlassian.net/wiki/spaces/LPDOC/pages/18382863/Aux+Mag+Setup+and+Calibration
see section "Set and verify AuxMagSettings.BoardRotation" but be aware that you should do it in the new Attitude->Magnetomenters GUI

And set Mag Usage to AuxOnly

[Rickolas]

All checked and looks like i have a GPS that is not as advertised. Was supposed to have an onboard mag, but after opening it up, the chip is missing. Board level etc look ok in librepilot settings, although i can’t see anything in the Librepilot documentation about using a GPS with the FC’s mag.

Oddly, if i switched the attitude estimation from GPS (INS13) to Complimentary+Mag+GPS, the drone flew level and behaved as expected, however gps flight modes didn’t work. When i set back to GPS (INS13) it went back to the unexpected behaviour and stacked it into the ground.

So i’ve ordered a new Neo7M along with some props to replace the broken ones.

Hopefully having a GPS+Mag combined, Should have it working from there.

[TheOtherCliff]

LibrePilot supports these GPS/mag types
- PixHawk (/ APM)
- OpenPilot GPS Platinum GPSV9
- DJI Naza

A Neo7M GPS is probably a PixHawk which has an I2C mag which means it has a second cable that must be connected to FlexiPort.

After installing a new GPS/mag you must do this:

in the new Attitude->Magnetomenters GUI

And set Mag Usage to AuxOnly

and re-run mag calibration