Sky High

Well, I just finished my NTSB investigation and have two theories as to why I crashed last night. I had flown this helo for four months doing all kinds of risky maneuvers at both low and high altitudes without incident. All this time, I had knowingly been flying with a motor mount that was glued together from a previous modest crash even further in the past and gotten away with it. Last night was just like any other except I added some new light sticks that I had just bought. They are very light weight and easy to use. They collectively weigh as much if not less than the new camera system so I know it wasn't too heavy. I had 3 perfect flights at low and high altitudes but the fourth was to be a disaster. I was simply hovering at around 30 ft when all of the sudden the helo started losing its hover and oscillating uncontrollably and would not recover no matter what I did. Suddenly it just nose dived and plowed straight into the track below. [X(] The damage would not have been nearly as bad if it had gone down in the grass just 10 ft away! [:@] Anyway, it was horrific, just like the other [link=http://www.rcuniverse.com/forum/fb.asp?m=3680056]fatal crash[/link] months ago but not as high. The noise of it hitting just resonated in my head and then watching it splinter into many pieces completed the nausea. I walked over for a closer look and just couldn't believe the amount of damage from such a short fall. What made it worse was I didn't even know why it had happened. After collecting all of the pieces I have two theories as to why this happened. One is that the added weight of those light sticks was just enough to change the flight characteristics and I overworked the motors and the other is that the lights' added weight put more stress on that glued mount than it could tolerate. I did smell something like burned plastic at the site and didn't know what it was. When I finally got home under some light, I discovered a burned up and severed capacitor on the the severed motor, the same motor that was in that glued mount. That's doesn't necessarily mean anything but is interesting. Strangely enough, the fuse did not blow! I must have cut the power just before the impact. I still can't figure out why that capacitor burned up though. Maybe it acted as the fuse since the fuse did not blow but the capacitor is just for one motor. So, I don't know if it was a motor/capacitor failure or if that motor mount came unglued and allowed the motor to oscillate therefore allowing the rotor to violently thrash around hitting the frame and bring it down. If the motors get too hot or overworked, could that have burned up the capacitor? I'm thinking it was the motor mount and therefore my damn fault for not changing it out. My circuit board was bent AGAIN! [:@] The vertical board and the Ti board were both independently slightly bent. I have carefully bent them back and am hoping it isn't shot. But, that damn CMOS video camera survived untouched AGAIN! Other than all this, I'd say I walked away pretty lucky.

Damage Report: (more images in post #2)

1 laminated rotor
2 landing struts
2 elbows
1 motor mount
1 broken main rotor gear
1 main rotor gear with broken tooth
1 main rotor gear slightly warped
1 decapitated nylon bolt (my first one!)
1 severed motor with burnt capacitor and bent pinion shaft
Detached canopy with 2 ripped mounting holes
Bent vertical cuircuit board 1-2 degrees right and bent Ti board slightly off horizontal
Decapitated power switch (just knocked that sucker clean off)

Relative Thread
www.rcuniverse.com/forum/fb.asp?m=3680056

Sky High

More Images

Hooch

Very sorry to hear bud. Ya, I learned the fun way that if you got a broken mount to just not fly hehe. I glued mine, but in my experience no glue seems to really bond well to the nylon or whatever the mounts are made out of. It appears to hold and does fly. But under any real use it seems to break loose. Hence it ended up crashing and breaking not only that mount, but another. So I have learned now not to do that hehe. Hopefully it wasn't the extra weight, but the extra weight added onto the broken mount might have definately attributed I would guess. I want to add more lights to mine, but now leary hehe, but I am still pretty confident it was the extra weight on your mount. And your theory about the mount breaking and I would think causing the motor to sit wrong and like you said forcing the rotor to thrash and cause more work for the motor and overheating it. Definately would cause a cap to freak due to the power draw.

Worse case scenario your motor is completely shot. Luckily they aren't too expensive. But no crash is a good crash. Wish ya a speedy recovery, but you have a spare anyways don't ya hehe. Good luck bud. Keep us informed.

Greasetattoo

My Feedback: (3)

Wow, that sucks!
At least you have your SAVs as backup!
How much do you figure the crash cost you??
Ebay???

TheHindmost

Very, very sorry to hear this, Sky High! I know you'll be back in the air soon with that DF! Here's hoping the circuit board survived yet again!

As for theories, another possibility is that the ceramic casing on the capacitor broke and started flaking off, due to previous stress, and then the capacitor itself started shorting out against the motor case. Or there was a break in the heat-shrink insulation on the capacitor leads, but they look intact in your picture. That would cause that motor to lose power and also burn the capacitor. It makes me wonder if encasing the capacitor in electrical tape would be cheap insurance against that particular failure mode. Ceramic is brittle stuff!

I think it's less likely the burned capacitor is due to impact damage, because you said you cut power before the impact.

Did you notice anything when the oscillation started other than the oscillation? Any rotor suddenly go out of true that you could see?

Again, sorry to hear to about this crash! But as Grease says, at least you have the SAVS to fly for now!

Will

Hunter850

My Feedback: (1)

Sky High,

Sorry about your crash. That one is going to be expensive. I have glued my mounts as well and the CA does not work very well. I have also used 2 part epoxy and it seems to work better.

Good luck on your rebuild.

Hunter

Sky High

Thanks to all for the support. I guess I was due for a crash since it's been a while. Because I haven't crashed in a while, I have just enough parts to get in the air except a main rotor gear. [:@] I'll probably need a new wiring harness too because of the motor seperation that took an inch of wire with it. The alternative is to pull the wire out of the tube and secure it externally and just add an extension.

Hindmost, that mount had come loose before while flying with no added hardware and I was able to recover and land. It made the DF wobble and you could hear frame strikes from the rotor oscillating. I think those extra few ounces of light sticks was more than it could tolerate this time. The solution is not to use glued parts again. One other possibility to the cause is that the battery could have shifted from the velcro and caused a sudden list in one direction. I have found the battery almost off of the velcro several times before but that has been mostly after some aggressive flying with quick turns.

As far as the other DF, well remember it has a bad case of the hiccups and is having issues with staying in the air right now. I'm going to try to resolve that today.

www.rcuniverse.com/forum/fb.asp?m=4095602

intrim

sky
sorry to hear of your misfortunes. I agree with the idea that one of the leads maybe shorted out against the motor. I started putting shrink tubing over thr capacitor itself after soldering
to the motor. also I put the cap on the opposite side than the way it comes. Im hoping it keeps it away from getting smashed comming in hard. so far the motors have alot of dings on them but the cap seems to be protected. also you can put a dab of silicon calking under the spot where the cap is going to rest.if you already have the cap protected you can push is right into (dap) and it will stay quite happy

madean

Sorry to hear about your crash, Sky. I crashed today myself. Lost one motor mount, and I don't have any spares, but have some on order...maybe next week.

Sky High

Thanks madean and intrim. The downtime after a crash is miserable. I noticed that I captured an image of frame strike marks on one of my laminated rotors. The image below shows the black marks from hitting the frame. They have been there for a while but this image actually shows them. Lamination is why more rotors weren't broken in this crash.

av8ersteve

My Feedback: (1)

Sky High, If it hadn't been for you telling and showing us to "laminate the blades", there would have been ALOT more Draganflyers go down because of blade strikes and failures. I understand your pain. I hope your not down too long, and I hope she flies better than ever when you get her back up flying again.

av8ersteve

My Feedback: (1)

That is an excellent idea! Never thought of doing that.

Sky High

Well thanks av8ersteve but I can't take the credit for discovering that. I'm probably the one that has run my mouth about it the most though. DFI recommended it a few times when I told them about frame strikes and broken rotors in mid-flight and when I discovered this board I read that several other people had done it but I just put it off and put it off until my [link=http://www.rcuniverse.com/forum/fb.asp?m=3680056]fatal crash[/link] back in November because of a frame strike and mid-flight shredded rotor. I was not going to let that happen again because of unreinforced rotors! And since I laminated them 4 months ago, I have had no problems with frame strikes. These same rotors were used for 4 months with as much as I fly. As you can see, the only one that broke was the one mounted on the glued motor mount. I think it broke only because that mount came loose and it thrashed the frame a few times.

nickruss

The parts are so cheap, I keep a frame with motors and wiring harness on standby, so if things turn fatal I just have to swap the circuit board which takes less than 2 minutes!

Sky High

Well, after further inspection, I found that I did have two cracked rotor arms, one in two places and the other in one. Cracks are easily hidden in these tubes. I have found that by placing your thumb nail next to the tube while slowly rotating and pushing it with your other hand, like a lathe, you can find these cracks when your nail catches on one. They just weren't evident by a quick visual inspection. I'm glad I found them before finishing the repairs and especially before soldering.

Sky High

Well, after what seemed like forever, I finally got the DF all back together and have had two flights with no issues so far. That circuit board is unbelievable considering what it's been through as far as 2 fatal crashes and providing over 100 flights over the last 6 months! I'll still be cautious over the next few flights though just in case.