So today i was spooling up my Goblin 700 with it's Spirit Pro (latest firmware) and it tipped to the right on spoolup.. I caught it before the blades struck and hit throttle hold. I checked the heli and the servo/swash response, all seemed ok so i gave it another try and had a normal flight.

So next battery I did some testing(this is with all stabi stabilisation turned off):

It powered up normally and the swash gave the standard 'jump' to indicate all is well.

With no power to the motor i applied cyclic aileron input and the swash at first behaved as normal. The swash tilted with stick input then when the stick was centred it slowly returned to 'level'.

I continued to apply aileron input then after maybe a minute i noted that the swash was no longer returning the 'level'. For instance if I gave it right stick input the swash tilted right and stayed tilted right indefinitely showing no tendency to return slowly to level like it normally does. This is without doubt what caused the near tip-over. The swash did still compensate normally if i picked the heli up and physically tipped the fuselage left right or back and forward, but when i returned the heli to the ground the swash remained tilted as per my original stick input.

So I cycled the sticks several times and eventually after a minute or so the swash started to act normally again, slowly returning the level after a stick input. I flew the heli and all was good.

I repeated this test on the next battery and got the same results, and the next battery too. It only shows up for a minute or so then goes back to normal behaviour. the only unusual thing today was that it was pretty cold, otherwise normal flying conditions.

So what's going on hear? It's quite dangerous because the swash staying tilted following an input on the ground causes a tip-over.

I have Spirits on several helis and have never seen this before, I'm very concerned that it's going to catch me out next time and I'll have a tip-over.....Any ideas?

maybe you have hobbywing esc with fan attached ?

Yes i do.. so that is a known problem?

So thinking about the reply.. i'm guessing the problem might be electrical noise from the fan transmitted back through the telemetry cable to the FBL... ?

Strange thing is I've been flying this heli for quite a few months and never noticed this issue before.

seem the hobbyking fan is making ultrasonic vibrations that make the spirit go nuts

look here

Thanks for this, it could easily be the issue. The problem was quite repeatable so i should be able to easily bench test to confirm that fan removal does fix it... it's cold here anyway so the fan isn't really necessary.

If it's confirmed we should probably be flagging up this issue on other forums. A toroid in the ESC telemetry cable might be all that's needed.

is not an electrical issue
is more a mechanical issue here ( ultrasonic vibrations)
so maybe the solution could be to mechanically isolate the fan from esc
with some rubber mounting
or as other user done, to replace the fan with another one

It's quite hard to imagine it's purely mechanical vibration. The ESC is a long way from the FBL unit on a Goblin and there is a lot of big heavy solid 'stuff' between the two.... But i'll not rule it out and I'll have a look at the vibration log with the fan both on and off. I have ordered a few Sunon 'Maglev' 30mm fans to try which should run smoother than the standard hobbywing one, so lets see.

The strange thing is that it seems to only happen shortly after powering up and it only lasts a minute, after that all is fine, it flies as normal.

So i did some checking on the bench. The Spirit vibration spectrum analyser cant detect any vibration at all from the HW fan, but this could be because it's at too high a frequency to be detected. My finger can detect a high frequency 'buzz' so clearly there is some vibration from the fan.

Frustratingly after this problem was showing up consistently at the field yesterday, I couldn't reproduce it on the bench today, so I can for sure say that the fan is the cause. To be safe I'll fly with the fan disconnected next time.

this problem about the fan was reported by many users here
and confirmed by thomas