Just bent my main shaft...

[Kamikaze_K]

...in mid flight! Yup, you heard right. Spooled it up, brought it up to a hover, then punched the collective. Once I was up pretty high, I pulled straight up, and let it fall in a nice tailslide. As I was pulling out, the machine started vibrating badly. I rolled upright, and landed as quick as I could. (actually hit throttle hold a little before I was on the ground) After some inspection and a slow, gentle spool up, I noticed that, sure enough, my main shaft's bent! I figure something's out of balance in the head... but no! I took a dial caliper to the flybar and paddles, and they're just fine, balanced my blades (CY Radixs), nope. The only thing I found is the top main shaft bearing on the frame is really notchy, and the inner race is really loose (probably worsened by the main shaft bending). Can a messed up bearing cause a main shaft to bend, mid flight? It's the only thing I've found wrong with the machine.

[josh mcormick]

...in mid flight! Yup, you heard right. Spooled it up, brought it up to a hover, then punched the collective. Once I was up pretty high, I pulled straight up, and let it fall in a nice tailslide. As I was pulling out, the machine started vibrating badly. I rolled upright, and landed as quick as I could. (actually hit throttle hold a little before I was on the ground) After some inspection and a slow, gentle spool up, I noticed that, sure enough, my main shaft's bent! I figure something's out of balance in the head... but no! I took a dial caliper to the flybar and paddles, and they're just fine, balanced my blades (CY Radixs), nope. The only thing I found is the top main shaft bearing on the frame is really notchy, and the inner race is really loose (probably worsened by the main shaft bending). Can a messed up bearing cause a main shaft to bend, mid flight? It's the only thing I've found wrong with the machine.

Sounds crazy to me! Seem like you would have to have an impact somwhere. Even if you had a locked up bearing its not going to bend a shaft. Where is it bent. Did you hit a bird? (I think i would sacrafice heli parts to be able top hit a good size bird, i have problems). Hope you find out what this is. Also check to see if you dont have a small hairline crack in the shaft? Im still kind of a newbe myself so maybe somone else will chim in with a little more knowledge:cheers

[notreallyme]

there was another thread about this a little while ago, but it just doesn't make since to me.

[sokal]

...in mid flight! Yup, you heard right. Spooled it up, brought it up to a hover, then punched the collective. Once I was up pretty high, I pulled straight up, and let it fall in a nice tailslide. As I was pulling out, the machine started vibrating badly. I rolled upright, and landed as quick as I could. (actually hit throttle hold a little before I was on the ground) After some inspection and a slow, gentle spool up, I noticed that, sure enough, my main shaft's bent! I figure something's out of balance in the head... but no! I took a dial caliper to the flybar and paddles, and they're just fine, balanced my blades (CY Radixs), nope. The only thing I found is the top main shaft bearing on the frame is really notchy, and the inner race is really loose (probably worsened by the main shaft bending). Can a messed up bearing cause a main shaft to bend, mid flight? It's the only thing I've found wrong with the machine.
make sure to check the upper flybar control arms before and after flight seems to wear the fastest

[ifheli]

I had been bending mainshafts almost every flight. I went to useing mini titan mainshafts. I had a friend drill a new hole to bolt gears/oneway on. Now I`m useing some custom made mainshafts from a machinist friend I have. I have not bent a mainshaft since I started useing solid shafts.

[Kamikaze_K]

make sure to check the upper flybar control arms before and after flight seems to wear the fastest You talking about the mixer arms on the blade grips or the washout arms? I'll be sure to check them too.

[sokal]

You talking about the mixer arms on the blade grips or the washout arms? I'll be sure to check them too.
washout arms to flybar rods upper ball link seems to wear out faster then the rest

[carlo_the_wonder_frog]

If the stock unit always bends and you arent hitting things , then you have a serious problem that isn't going to go away by using solid shafts. A very worn bearing can easily cause a shaft to bend, these things spin very fast and any part that is not concentric is going to cause problems. replace those bearings.

[ifheli]

Well, I can say there is not a thing wrong with my bearings or on the helis. I started bending shafts right off the bat as in new out of the box. I even built one b400 the expensive way by buying parts off the wall. I was flying it at first as hard as my 450SEV2 and never made it more than two flights without bending a shaft.My bearings are very smooth as were the helis untill the shafts bent. After installing new solid shafts my problems went away even flying the same plastic head parts. If I had other problems, I think my B400`s would be vibrating like crazy. I now have trex V1 and V2 heads on both now. I have not even bent a spindle since installing solid shafts. For now I have backed off on how hard I fly them compared to my 450. I have never bent a mainshaft in flight on 450 which has a solid mainshaft. And both B400 were balanced from the beginning and balanced again after every bent shaft. They have even been torn apart to look things over after the in flight bendings.

Keith

[OCD 4 RC]

Key items:
Your top frame bearing for the main shaft is notchy and not spinning freely.
Your bearing to shaft tolerance is loose.

I would suspect that the main shaft shows signs of heat. i.e. either black or varying shades of blueing.

My guess is that the bearing spun on the shaft heating it to a point that it became malleable under the stress that you put it under. Your GOING to have imbalance, youll never get it perfect. And at 2500 RPM at the rotor tips you have 4200 G's (G-force) With ONLY 0.001 grams out of balance, and I dont think you would be able to get it that close, you would have the equivelant of hanging a 4.2 gram weight on the end of one of your blades. All I'm getting at is that the shaft heated up, weakened the metal enough to let it give in to the imbalance. My $0.02

[Kamikaze_K]

Alright, well I just replaced my three main shaft bearings with nicer Dynamite sealed bearings, replaced my washout base and arms, main blade grips, bell mixer arms, and ball links to the flybar. Basically everything but my head block, thrust bearings, and blade grip bearings. If this thing still vibrates, I don't think I'll have hair on my head for much longer. Thanks for the help! We'll see what happens.

[Kamikaze_K]

Just finished installing all my new parts. It feels MUCH better. It's very smooth now, and the head feels much more precise too. I've been flying it pretty hard over the last few months, and I guess it was just time to rebuild a few things. I spooled it up about 1/3 to 1/2 way, and when I hit throttle hold, there was absolutely no wobble as it spooled down. I think I've got it back to abus--er... flyable condition. :thumbup:

[Wayno]

Yay!
:P

[ted_wears_a_hat]

Alright, well I just replaced my three main shaft bearings with nicer Dynamite sealed bearings

What are the part numbers for these bearings? One of my local shops stock Dynamite so it would be nice to know.

Thanks. :thumbup:

[Kamikaze_K]

DYN3215 5x10mm unflanged ball bearing. These things are smoooooth. I just threw it into idle up today, and it's still smooth, so I guess I'm back in the air! Now if this dang wind will just die down. Grrrr.

[Kamikaze_K]

Oh you guys won't believe this... I just bent another main shaft. :arggg: The good news is that I think I know what's doing it now. My canopy. You heard right, my flippin' canopy! I've got the Align fiberglass T-Rex canopy on it, and I've mounted it by just sliding the stock mounting rod behind the anti-rotation bracket. It's a pretty tight fit, and over the last few days, it's managed to distort my frame. The shaft slides right through the top two bearings, but it needs to be pushed into the bottom bearing. Hooray for non-adjustable bearing blocks. :thumbdown: I've now got it hanging in my garage by the front gear struts with my Dremel tool and case hanging from the anti-rotation bracket screws. I'm hoping I can un-distort the frame this way without having to replace the frame. Cross your fingers, and find some wood to knock on.

[Kamikaze_K]

Another update: I just hovered two packs through it in my driveway with the canopy off, and no vibes, or bent shafts! Yay! I'll be putting T-rex 450 canopy posts on it shortly which should help take the stress off the frame from the new canopy.

[newhelliguy]

glad you are back in the air. I had the same problem you mentioned the shaft would slide through the two top bearings but not the lower. I heard on finless videos to tighten the frame screws from the middle to the outside of the frame to prevent distortion. I loosened all my frame screws and tightened the from the middle out. Started by the bearings and moved outward. after this my bearings lined up much better. Maybe this will help thank Finless.