Newbuild / 3.5.7 / Crash

Hey all,

In the process of building a TBS Discovery framed quad with the Pixhawk 2.4.8 hardware. I have limited knowledge and have dived in at the deep end. Yesterday I have a very brief ten or so minutes flying the drone on the stabilise and RTL mode. Both seemed to be flying fairly steady although there was just initial tests without any real flight stresses. Today, without adjusting anything, the craft refused to return home and ended up crashing. I have damaged a motor and possibly an esc. In any case, would a kind soul help me to try and understand the flight log info,. I am barely able to read the logs on APM planner, regardless or resolution,
and I certainly can make little sense of the data. Would be interested in any educated observations, before I chuck the dam thing and buy a RTF or NAzza lol.

Many thanks,


First you launched the craft before you had any GPS satellites received. W/o GPS lock it will not RTL of course. Graph Baro>Alt vs GPS>Nsats and see what I mean.

Secondly you have something going on with your Rc Inputs. All channels show the same wild swings/glithes in PWM value. I don’t know how this craft was flying. Graph RCIN>C1-C5 (AETR & Flight mode) to see for yourself.

Mate, thank you for taking the time to reply. Steep learning curve but the Sat side of things seems a little obvious when you point it out :slight_smile:

As for the inputs, I will attempt to have a look at the area you identified and see what its showing, although addressing this may present problems haha

Yip, it does look all over the shop, but again to the untrained eye, its means very little. Would you suggest this is a controller issue (Taranis x9d plus) or issue with receiver (Frsky X8r) ?

That’s usually a fairly bulletproof combination. Power looks OK. An intermittent fault between the Rx and FC maybe. Sbus out of X8R to RCIN on Pixhawk right? Check that lead maybe. Are you running OpenTx on the X9D?

Wait a minute. It doesn’t look like you have performed the mandatory calibrations. You have no compass offsets recorded (compass cal required). It also doesn’t look like you calibrated the radio either which is likely the problem with the RC input. I would suggest you step thru the mandatory calibrations. Accel, Compass, Radio (don’t use the Wizard). On the radio calibration screen make sure you flip all the switches related to flight modes. In fact just flip all the switches and turn the pots/sliders fully thru their range. And of course the sticks.

Thanks again Dave for the help. I had completed all the calibrations listed the night before. Do I require to do these on every occasion I use the drone?

I have indeed connected the units as described. I shall await the new motor, calibrate everything and log some hover with simple inputs to see the log results. Hopefully that will give me insight.


Hec-No, those calibrations typically only need to be done once unless some hardware has changed. After a crash you will have to do it again. For sure the compass calibration didn’t complete or take or the offsets would not be at zero. The RC values look suspicious also which is the Radio calibration.

If you don’t have any telemetry back to a ground station or on your Taranis then take off in Loiter mode. It won’t arm unless GPS is satisfied.

Or set a geofence, then it wont arm in any mode until a satellite fix has appropriate accuracy.
It save a lot of trouble, and you have time to stand around and think while you wait for GPS fix.

Thanks guys, so I took of the props, calibrated the radio gear and ran the drone on the desk for a 10 seconds or so. Does this RC input look any better?. (basically I moved the sticks to most positions in slow deliberate movements). Is this even a valid test when its not propped and flying??lol

Thanks, Hec

That’s the KMZ file.Post the .log or .bin.

Well spotted! :slight_smile:



Not much can be learned from that log other than you still haven’t calibrated the compass. Why not? It’s mandatory. Your flight mode channel shows no change in that log so if you were flipping those switches, which you should be doing during radio calibration, it’s not working.

Maybe you should start at the beginning:

Hi Dave, I hadn’t calibrated the compass as I broke the mount when it crashed. I didn’t see that this would hold me back from a short hover to test inputs.

In any case, I think the problem may have been down to a dodgy connection on the receiver. I noticed today if it was tapped a certain way that the unit would loose power. A second tap would correct it. On closer inspection the power lead in the servo wire is broken and needs a wiggle to correct. This has now been rectified and once I have repaired the damaged compass mount and got new props I will see how she goes . Thanks for your help its much appreciated.