Could someone please tell me what this means, or what would cause this error? Twice my quad has just flipped over and hit the ground.

And no it’s not a motor sync issue as I’ve already ruled that out and have not had any issues with the motors stopping and restarting at any RPM .

the attached log does show such problems.

Sorry wrong log file, the is the right one.

The error says it’s unable to enter RTL mode.
Because you had no GPS fix.
Regarding flipping, search for motor sync problems, and verify that your motor/prop/esc/voltage combination is fine, that’s the most common reason to a flip.

It’s not flipping over at takeoff, while changing altitude or giving it throttle. While in a hover It will just randomly tip over like one motor slowed down and the rest of the motors speed up dramatically causing it to come towards me and flip over just right before it hits the ground. I bench tested the ESC’s and motors for sync issues and everything is fine. The motors have no problem starting, stopping and restarting at any speed. So I’m pretty sure this is not a sync issue. Today I slapped on an old CC3D board, and have no issues with the motors or this ESC combination.

I didn’t have any issues until I updated to the most recent firmware 3.1.2

I put the Pixhawk back on last night and took it out for a flight this morning with a lower 16 pole emax motor to rule out if it was an issue with Simonk firmware and high pole count motor and yet again I get same type of crash happening again.

One motor appears to just slow down for no reason whatsoever and the other three motors speed up causing my quad to crash not even 3 minuets into the flight. This is really frustrating since all i done was upgraded Firmware which greatly improved Loiter and Alt hold performance, but now is giving me random crashes as a side effect.

Emax MT3515 -650kv 14x.4.8 T-motor props
ESC T-motor S45A SimonK

If you have a Tiger S45A ESC and use it along with the Pixhawk FC, you need to remove the red wire from the three wire signal lead on your ESC’s to use it with the Pixhawk. I suspect that somehow the power priority circuitry on the Pixhawk power rail is somehow causing or allowing noise to get to signal lead which is confusing the ESC and causing lower KV motors to randomly either slow down or completely stop. Some are calling this an ESC sync issue, but an o-scope is showing me that there is electrical noise present.

This is what my motor/s would do in flight.

This is sort of what I was seeing on the oscilloscope but not as drastic or as frequent.

Those say they have no BEC… Are they optoisolated? You may need to provide them 5v. Have you tried adding a BEC to the servo power rail?

Yes, they are Opto Isolated ESC’s and they don’t need 5v to operate. Yes, I had tried using a BEC that puts out 5.8V to override the power from the Pixhawk power module, however the problem still existed even with the 15A BEC as well.

I had seen some post and videos where guys using Hobby King AFRO’s on an older Simonk Firmware were having ESC sync issues only using just the signal wire from the ESC and not connecting the ground or the positive. Some of them had plugged their ground wire from all the ESC’s to the power rail, and they no longer had issues.

This gave me the idea to duplicate connecting my ESC’s using only the signal and ground for the tiger S45A’s and this seems to have resolved my problems as I had thoroughly bench tested with success as well as got down 15+ flights with no issues at all.

[quote]When wired up correctly, we never saw an issue nor could reproduce issues users had when 3DR wired up their gear and tested it. You might want to get the guy to take a couple of pictures and draw a wiring diagram.

Despite the incorrect information in that thread, the ESCs are NOT powered by the power module, nor does Pixhawk draw from that rail under normal circumstances. Are those ESCs providing 5V output? In case they do: Are they specced to be OK to have their 5V outputs put in parallel? Because most linear regulators are not and most ESC manufacturers just elegantly ignore this - which is why the common recommendation is to remove the center pin on all but one ESC to play safe. It is by default NOT ok to wire multiple ESC +5V outputs together (or to plug them together into a receiver / autopilot). You can get away with it for some, but its not correct nor safe.

Signal integrity issues are in the majority of cases a question of correct and reliably wiring, and so this is always the first thing to check. There is no magic in the autopilot - if the wiring is correct, it will work.