Close call with the Gob 500

pvolcko

Well-Known Member
No Vid.

Just took it out for a flight. All was going well until 3 minutes in or so. Then the collective started getting very sensitive in both positive and negative. Borderline uncontrollable at times. I managed to get it into a stable hover and thought whatever was going on had resolved (was thinking maybe low voltage in the pack or some kind of cold temp effect on the Ikon). Gave it the slightest positive pitch to climb a bit away from me (it was a little too close for comfort given what had just happened) when it started to jump around again. Got it within 3 feet of the ground and relatively level and then hit TH and autoed in. Luckily got it down in one piece. On the ground collective control appeared to be responding fine. WEnt to take the canopy off and disconnect the pack when I noticed the front servo was loose from the frame. Odd. Turns out both screws holding the mounting plate to the top frame plate were missing! So I was more or less without control on the front left swash point. Not sure why this presented as collective control problems as opposed to cyclic. I suppose the anti-rotation bracket and two positive points of control on the swash and FBL roll rate control were enough to make cyclic manageable.

Can only assume this was a result of the cold weather. IT was the first cold weather flight with it. May have used too little thread locker on them and with the contraction of the metals being different it made the screws break loose.

Or I forgot TL on them when I was building it and it just took the cold to make them have enough room to back out?

Will have to go through and check everything and re-TL again.

Got lucky.
 

Derek

Well-Known Member
Whoa! That sounds exciting...and not in the good way. At least you got it down in one piece and you were able to find the culprit.
 

pvolcko

Well-Known Member
Just have to find some screws that will fit. :)

Crashed the 550X the day before. Mild, just took a tooth or two off the main gear. Put it right back up in the air to finish off the pack. Gotta love snow for crash damage prevention. :) Got that on video, hopefully get it posted soon.
 

teleman

New Member
Sounds like savatage Lee… I understand vibration and such, but those screws can't possibly both back out that fast ; can they ? Im thinking someone had a few drinks with the tunes cranked and forgot to put screws in at all…. its ok, I understand…lol JK…
 

pvolcko

Well-Known Member
Well, I fixed up both the Gob 500 and Blade 550X tonight. Gob: Checked all the screws on the heli. Turns out all the screws holding the servo mounting plates to the transmission top plate were on the borderline of starting to back out. I took them out one by one and put some TL on them. I have a suspicion that I forgot to TL these guys when I did the original build. Guess that speaks to the relative lack of vibration in this thing that it took pretty cold temps and several flights before they started to back out. The I found one screw near the front frame that loosened easily, but it would not have backed out any more than a 1/8 turn due to thread locker. I re-TLed and snugged it back down. The two screws holding the tail slider arms to the slider/spinner were not backing out but they unscrewed too easily for my liking so I re-TLed them too. Otherwise all good, including head and swash.

550X main gear replacement was no issue. Checked all the screws. Small ones on the swash driver arms were a bit too easy to back out so TLed them again. The screws securing the servos to the frame came out too easily (doubt they would have backed out since I used rubber grommets on them). Re-TLed. All good otherwise.

Will give the two 700's a once over before flying them, too.

So if you're flying in cold climates this winter, give the helis a once over either before taking them up or after the first cold weather flight. The smoothest running models may have issues that get exposed due to the temps.
 

Tony

Staff member
One thing that people do is they DO put thread locker on the bolts, but they forget to clean the oil off of them first. I have seen this quite a few times with bolts backing out. Mainly on the feathering shaft since it's a polished steel piece, but it does happen elsewhere. Glad you were able to get it down.
 

Ken Jackson

Active Member
I try to go over every screw after 6 or so flights. Before I plug in a battery I always check all the swash screws, all the servo screws and ball links. And always check the tail rotor, mainly the screw holding the control arm and the screw holding the ball link on the control arm. I guess when you have crashed before by not looking at those things it becomes a habit. I have had crashes because of all the things I just listed.

The crash I had because of the control arm ball joint coming out was because I trusted the manufacturer and didn't check to see if they thread locked it. I don't trust any parts anymore unless I look. I spent too much money learning to fly and now its time to enjoy flying!

Ken
 

pvolcko

Well-Known Member
I checked everything over after the first flight and the third flight during the end of the summer. NO issues. I'm guessing the screws on that one area were not thread locked but they were torqued down pretty good. When I check things over I try putting a bit of backout pressure on each screw into metal but not enough to break it loose. The torque likely held at that point so thought all was good. Temp change and several flights more and the high frequency vibes of the servos on hard mount (no rubber dampers on these, as per the manual) must have worked them loose over time and without TL they backed right out.

When I took the pair of screws out on each of the other servo mounting plates they came out very easy and they appeared clean, so I'm pretty sure they never got loctite on them at build. Everything else did.

Always clean screws with alcohol and a twirl in a towel before loctiting and installing.

I'm not sure why I would have mounted these with the full torque without loctiting them. This was my third build and never have done that. But this was first gob and it has an odd servo mount scheme compared to blade and align. Maybe was thinking I'd need to redo the servo mount to get the proper servo mount to ball distance (goblin build is very specific about it). Not sure what else I can do in the future to avoid it. I never torque things down, normally, unless I'm loctiting them. And if my normal back torque check isn't enough... Kind of one of those oddball oopsies I guess. Will have to be more careful about not torquing before LTing in the future. And also do screw torque checks on every bearing lube check (every 10-20 flights).
 
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