Hey all. I am a newb who just had his first non-minor crash.

I would love help on this specific crash but I am also looking for advice on troubleshooting steps to take after my many future, inevitable crashes :)

On to how I broke my baby.

I am flying a 3dr hex that I bought RTL. 850kv motors, 10x4.7 apc SF props, 20amp ESCs, 5000mah 3s turnigy bat, and the most recent versions of APM and mission planner. I am using the 3dr telemetry and a spektrum 8x tx.

I was testing autopilot functions. After 4 successful flights of takeoff - waypoints - land/RTL my hex fell out of the sky. I can't figure out any easy explanation. 

I have tried to diagnose the crash on my own. I figure that if there was a specific motor/esc problem that there should be a spike or dip in one of the servo channels. If there was a compass problem then my offsets would be too large. If my earplug vibration dampening system wasn't working then it should not have flown the prior flights. I can't find any of these issues represented in the logs. In fact, there are no outlier spikes or dips that I can see in any of the logs. I have attached them in case that helps.

I got video of the flight. No noise or strange movements are noticeable to my untrained eyes/ears.

Crash Video

I couldn't get the voltage to show up in mission planner so I figured I would keep the airtime at<5 min. After the flight I measured the voltage using my charger and it read >11 volts.

The only strange thing is that, as far as I can see, all the logs cut out before the crash. But in the video the motors don't shut off. 

Any thoughts on where should I look next? Did I miss anything?

Thanks for your help in advance.

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Update: I am testing it post crash. I armed and put the motors at full throttle (without props). Sometimes the motors will lose power, dropping to < 50%. When I power down I am unable to re-arm. This happens ever 3rd or 4th time.

Here's the video.

That is too bad and with the video it looks like the 'drop' side motors lost it.

I will look over the tlog and be right back.


Are you using the 3DR Power Module on this aircraft?

Here is your Vcc graph...(over the time of the entire log - didn't mark the actual flight time section)

Vcc is 5VDC for the APM before regulation to 3.3VDC (on the APM).

It looks to me that your Vcc is falling out of spec. It is cleary below 4.7VDC near the end of the flight.

This graph should be as flat as possible..I mean dead flat (in a perfect world).

You are hardly near 5.0VDC for any length of time. A good setup for a brown-out/reset.

Watching the log playback, around 97% the motor state went from DISARMED, to ARMED, to nothing.

I think your APM reset due to Vcc dropping too low.



Big time thanks for the input, Doug!  Do you have any recommendations for next steps to take?

My friend who is working on this with me is the electronics guys. I will speak to him about the voltage problem. I do know that I am using a 3dr power module but I hadn't enabled it. We were planning on limiting flight time until we could get the multi-meter and the drone in the same room at the same time to calibrate it using the board-measured voltage. 

We left the drone plugged in between several test flights which is what I think you are seeing in terms of the armed/disarmed motor state. The failed flight is at ~95%. 

You are welcome.

Keep in mind that the recording of the 5 VDC is not continuous. The graph displays a data point. The voltage could have been much worse between data points. When zoomed in you can pick out the points and only guess what was between them.

The fact that the 3DR module has not been enabled is why you have no recording of the battery information in the log. When enabled, it collects that also (and current). Use the instructions located HERE.

I could see that you had several cycles of disarm/armed implying pauses between flights. As the MP screen cap shows at the end, there was a loss of that indicator on the flight data screen. I think this implies a software crash on the APM, most likely due to a brown out.

Ideal reading for Vcc is just over 5.0 VDC..all the time. Practical values will be 4.85 and above. Yours was often below operation specification.

When you enable the 3DR power module, you will see if your battery is actually keeping up during loads. It probably is but you can assume nothing until you have some data to work with.

The short 'fix' is to add some capacitors to the Vcc. With the 3DR module, this is more problematic as the connector is not the usual 'servo' type which is supported with aftermarket capacitor products. I suppose a cap could be added to the module but this would probably void any warranty on the module.

This may require more thought and input from others.


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