Crash - any theories on what may have gone wrong?

[mjc1970]

Unfortunately I had my first crash with my Trex 600 ESP last night. Having notched up over 50 flights with this helicopter I'm still a little confused as to what happened. I would be the first to hold my hands up and say it was pilot error, but I know in this instance it wasn't as a result of anything which I caused on the controls.

This therefore suggests it was either a radio glitch or something mechanical however I do not have sufficient knowledge to state whether it was mechanical or not.

The conditions were breezy with about a 10-15mph wind blowing. I've flown many times in these conditions, so I didn't have any problems about flying in similar conditions. I did my usual pre-flight checks and checked the blades and all ball joints were in place before proceeding to take off in idle up 1 mode. The helicopter was hovering fine for over a minute and I was just about to turn it 90 degrees right to do a circuit when all of a sudden the helicopter pushed down like it was doing an extreme 3D manoeuvre. I reacted instantly to this and applied enough collective to push the helicopter back in the air to around 30 feet. Almost instantly, the same thing happened again and there was no stopping the sudden fast downward movement this time where it went heavily into the ground. I quickly hit throttle hold and the helicopter lay there having broken both main blades, stripped main gear, broken skids, bent fly bar and some missing ball joints.

Foolishly, I turned everything off before checking if the Spektrum AR8000 had a flashing light on the receiver. I just wanted to make everything safe asap.

If anyone has any input into what is the likely cause then it would be appreciated. Other than obviously the damage caused, the worst thing is really not being able to explain what truly happened. Having described what happened to a couple of other pilots, the most proably explanation is radio glith. My updated DX8 has been fine up to now.

Any help would be very much appreciated. Thanks and off to the heli shop now to work out a parts list!

[paulmedford]

was the heli level when it went full negative? if not, from my experience, a pitch link could have come off, it happened twice with me with similar behavior as your heli. I would suggest you change your links to rocket links, as an upgrade , even though it may not be the link in this case, its worth it as an upgrade.

[pril250]

Hi, sorry to hear of your crash, quite frustrating in it self let alone not knowing the reason. Is this heli flybar or FBL and are you using a satellite with the RX. Information on a brownout would have been helpful but once you get your electronics up again, before changing anything test the swash reaction in an induced signal loss (switch the TX off) and see where the collective pitch and cyclics ends up.

[mjc1970]

Thanks for the feedback chaps.

Yes the helicopter was completely level when it made it's two plunges vertically to the ground.

It is the flybar version and the radio setup is a Spektrum DX8 linked to a AR8000 receiver with satellite. The best of it too, I even have the telemetry module attached which would have shown any fades and holds. It was just one of those natural reactions to get everything turned off asap, without thinking about it and still scratching one's head why!?

I will try the simulated brown out later by turning off the radio and see what happens.


Thanks once again

[ahahn]

Not sure how the AR8000 handles failsafe (or any Spectrum receiver for that matter!), but I wonder that if you bind with the collective stick at the bottom (for throttle off), do the cyclic servos pick that up as the failsafe position---full down?

If so then something like a glitch or perhaps static might give rise to full collective down, at least until the receiver can recover.

Just guessing here.

[kimmik]

I agree, check if fail safe is set with full negative pitch. Power on electronics and receiver, wait till everything initializers, then switch off receiver.

If the servos go to full neg pitch, then start looking for why the signal might have dropped out in flight. Do a range test. If range test normal, consider possibility of a jamming signal at the flying site that day. Did other people fly fine that day?

Btw I also occasionally experience sudden full FoRWARD pitch commands on my ar8000 setup, even though the tail boom is wired to frame already... Usually occurs on first flight, then not again for the day...

[seanh]

test your servos. Typically people simply move the sticks and look for reaction...only part way there.

When you're testing servos you need to hold your servo horn at the same time. This loads the servo for proper testing. I've had servos work well with stick movement and lightly holding the servo. But, if I held it tight (not stalling it- just not lightly holding it) The servo would fail. Also try turning the horn by hand when powered.

Sometimes servos simply go out but this test will help identify that before you get in the air.

[rcflyerheli]

I'm not positive on this but if you were running in DSMX mode, you won't get blinking lights. Because the DX8 uses active channel switching, it doesn't blink like the DSM2 receivers do.

I ran a bunch of tests on my Vbar with 3 Savox 2271s (which are known to draw higher than average current) using a 2500 mah NiMh and during repetitive cycling of the sticks, I could force a brownout with the servos and RX. What i would see is the servo didn't go anywhere on its own, but when the brownout occurred, it would just stop for an instant and then restart its movement. The satellite lite would blink off, and almost immediately reestablish a solid satellite lite until I wiggled the sticks and caused another brownout. As soon as the servos stopped moving the voltage recovered and so did the system.

About running in DSM2 mode if the same thing happens - I might guess you would see blinking lites, but I don't know. I can't see running the older DSM2 when you have the DSMX available.

[ddj74]

OWB slipping?

[heraldo]

I'd say the fail safe kicked in.
Noobs are often mislead by the spectrum manual. I fell for this Aswell but didn't have this problem.
It says bind with zero throttle. Noobs often just push the stick all the way when binding. I bind at mid stick with throttle hold or a zero percentage throttle in normal mode


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[Corinator]

definitely sounds like your failsafe kicked in. Sorry for your loss. Was your Rx pack fully charged?

[satgod]

I got tons of ideals on why but the main reason is

the Heli met gravity and then found out how gravity works

but seriously without being there to see it, its all speculation
I would guess brown out myself
this will help with brown outs
http://www.hobbyking.com/hobbyking/s...dProduct=17100

[mjc1970]

Thanks for all your feedback. Having repaired the heli, I'm 95% sure I have found the cause of the crash.

I believe it's down to a faulty switch on the Align Voltage Regulator. I have noticed that even with the switch turned on, if you apply just a slight bit of pressure or vibration, in some instances it resets it's self! I'm sure this is what happened when by heli took two sharp pushes back towards the ground. On the second occasion, it didn't reset itself in time!

I've subsequently ordered a new voltage regulator and will test this theory out, but it seems for now the DX8 and radio issue are not the likely cause.

Cheers.