General First 'crash' yesterday

[mooserider]

Well, I was out yesterday making tail adjustments and test flights yesterday and had my first 'incident'. Things were going well... I went through three batteries and was on my last. The wind was kicking up, more than I should probably be dealing with, and as I was setting it down, it pitch right too much and the rotor blade whacked the ground (grass) a few times, so I yanked the throttle down.

I go and inspect things, and nothing appeared damaged. Grass and mud on the rotors was about it. Gears, servos... everything seemed fine. So I figured I'd spin it up slowly and see if anything seemed odd. No odd sounds, no gear mesh problems... so I get it up to full throttle and hover it about 10 or 15 feet up. Just hanging there, and I'm looking at the tail rotor action again before I leave.

Well after about 30 seconds, there was a loud "POP!", and off go the rotor blades in different directions! The body just dropped to the ground. Turns out that one of the two bolts holding the rotor grips ripped in two. I'm guessing the stress on it from the first hard landing and the rotors hitting the ground caused a stress fracture in the bolt.

Those blade coming off caused a bunch of other damage... stripped all three servos, broke a few linkage arms, stripped the tail drive gear, bent the rotor grip arm, cracked rotor blade, and lost some of the thrust bearings. Pretty brutal for what seemed like a minor crash at first. I can't imagine what would happen by dropping that thing out of the sky at full throttle and wrecking!

Should have it ready again in a day or two... gonna have to re-90 everything, level swash, 3gx setup... all that fun stuff.

Let me know if there's anything else I should take a look at that may not be obvious.

 

[Admiral]

Sounds like your doing an almost total re-build anyway, I would probably do all the repairs that you have identified which should get it back to ready to fly then fire it up at low revs without any Main or Tail blades. That should give you some indication if there are any underlying problems that you haven't found yet such as faulty 1 way or bent motor-shaft.

 

[Lee]

I just forked out $315 for one crash of my Goblin 570

 

[Tony]

Was this an Align helicopter or a clone? Don't usually hear about Align bolts snapping like that. Maybe next time don't tighten those bolts as tight. Snug them down pretty good and let the thread lock do it's job. Just a thought. Sucks about the crash bro. Hope you get it going really soon.

 

[mooserider]

It's Align. But I've been buying extra parts here and there, and accidentally ordered 13 servos instead of 3! So I have backup. I think for everything. I also ordered a set of the of the RC Screwz for it from amain a few weeks back. Hoping they won't strip as easily. Maybe I am putting stuff in too tight. Using thread lock too, and probably too much. Just so paranoid about things vibrating apart. Airplanes are much simpler...

Anyhow, I stripped it down last night, starting on fixing now!

- - - Updated - - -

Oh by the way Admiral, thanks for the advice, I'll try that. Didn't think you were supposed to rev it at all w/o the blades on it. Just keep it really low I guess.

 

[Tony]

Holy crap, 13 servos? Dayum, hook a brotha up!!! lmao. I need to order servos myself for the SE V2.

 

[mooserider]

This is kind of neat... thought I'd share it. I don't have any special tools for checking that the servo arms are 90 degrees, so made one using some of the push rod 'adjusters' from my planes. Got the idea from a tool I saw online that you screw into the center of the servo with a long rod on it.

 

[Tony]

Dude that is fantastic! Love that setup.

 

[mooserider]

I have a question about using a replacement bolt. There was only one thing I didn't have as a replacement... a 'socket collar screw' that holds the blade grip arm to the blade grip. It's an M2x12mm bolt, where only the end is threaded... the bearings in the arm rid on this bolt.

I do have fully threaded screws that will fit no problem... but that means those bearings will be riding on the threads instead of a smooth bolt. Can I use this temporarily, until Monday when I get the proper replacements? I don't see those bolts taking a ton of load, just a little up/down for the rotors.

I'm dying to go back out there and fly... so talk me out of this if it's really a big deal please!

Thanks!

 

[D.O.G.]

Hey there mooserider, you're taking chances with the blade having a better chance of coming off and hurting someone or some thing. My opinion i would wait.

 

[mooserider]

Ya, I decided to wait it out. Impatience will just end up costing me more repairs. Thanks!

 

[mooserider]

Well, I got it back together, but I have a problem. When I get it spun up, right before it's ready to lift off the ground, it starts shaking pretty violently. Happens with and without the 'sticks' on it. I'm not sure if this is sign of a mechanical problem or a gyro setting. Before it crashed, I was messing around with the gyro settings, but I don't remember it shaking like that ever, so I'm leaning towards it being mechanical. But getting up to speed it acts fine... it's literally just one click on the throttle and it starts shaking like crazy.

Before I went to try and fly it, I had it spun up with the blades off to see if there was any wobble in the main shaft, and I didn't notice any at all. I could always replace it... just a bit of a pain. If this was a gyro problem, what setting would most likely be the culprit? Gyro sensitivity?

Thank, I appreciate any help/advice you can give!

 

[mooserider]

Well, I think I'll switch out the main shaft. Can't seem to change the behavior in software. Can someone help me understand the difference between the two 3GX settings:

- Rudder locking gain adjustment (in Rudder Parameters). Current: 52 out of 100
- Rudder gain (in Settings Display). Current: 99 out of 120

When trying to set the tail wag, I'm guessing it's the second setting?

Thanks

 

[Tony]

If I'm not mistaking, the first one is pretty much HH mode and the second one is Rate mode.

 

[mooserider]

So that screen (Settings Display) is basically the "current" settings, I guess. None of them can be modified on that tab, it's just what's going on 'right now'. When I toggle the HH/rate mode, it will switch from 99 (rate) to 111 (HH) in the UI. If I move the ail/ele gains on the 3GX, they update in the UI. But you can't 'set' anything on that tab.

So I'm back to researching the difference between the head locking gain in the 3GX and the gyro gain in the TX. There's so much miss information out there from people that don't understand how to properly set up the 3GX. It makes really understanding this stuff a challenge for a noobie. I spent at least 3 or 4 hours last night reading old threads on the tail swinging out on hard positive thrust. There are so many possible mechanical causes I learned about (low head speed, tail rotor bearings under load, lack of tail blade pitch), as well as 3GX settings issues, and even bad gyros in old hardware. But everyone talks like they know exactly what's wrong on these threads when people post. Others will just give up and switch to a different gyro brand. It'll be worth it once I'm over the learning hump though.

But I did get the vibration fixed... I replaced the main rotor shaft and that didn't do it. It came down to two things that helped. Replacing cheap blades with align blades took out about half the shake. The other was turning down the ail and ele gain on the 3gx (the screws). Back to where I was now before the crash. I have some tail issues still, so I'm going to go back to the thread I created for that.

By the way, I'm sure you guys know this, but I never hear it mentioned. People always disconnect their motor or use throttle hold to avoid spool ups in posts and videos and such. I use my receiver battery in the 3GX so I don't have to even use the heli main battery. No spool ups to worry about and everything stays connected on the heli. My guess is most people that have helis don't have a receiver battery.