Unexpected behavior, pitching rearwards on takeoff

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 in LibrePilot 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
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?

Check the board origination in LibrePilot.

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, 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 GPS from @unmannedtech along with some props to replace the broken ones.

Hopefully having a GPS+Mag combined, Should have it working from there. If it does, @unmannedtech will have another order for a GPS from my mate who has the same issues with his Revo too :slight_smile:

I have not flown librepilot for some time but abit odd that not having a compass would cause the quad to flip out in GPS mode :frowning:. But i know it wouldnt work anyway without a compass. Hopefully the new modules will solve the issue

Interestingly enough the latest betaflight can fly in GPS rth without a compass, although it does fly badly, but it only uses GPS, but I’d it’s not setup properly it can still freak out and crash.

Well i managed to sort out the GPS last night after it arrived. Downside is i mistakenly thought i could remove the pins from the existing molex plugs and place in a jst :man_facepalming: (i hadn’t realised it was supplied with molex) so had to strip back 2 spare wired 4-pin JST’s and solder them to the GPS wiring. Connected up, programmed, and showing up in the live data.

Unmanned tech gps works, shows satellites, and appears as an aux mag now, meaning it shows the differential readings of onboard and aux mag. Flight Data tab is showing level which is a start. Just need to get outside and calibrate it now.