Vibration problems...I think?!?!

[J-Heli]

Okay. I have a couple problems. The last few flights, when I go to spool up my Gaui, the tail boom vibrates pretty badly, and then at higher RPM, it looks like the vibration goes away, but I'm not sure if it goes away or that it vibrates it so fast it looks like it goes away. Is this normal?

Secondly, I think that the whole head assembly is vibrating vertically, and maybe causing the tail vibration. What could cause this.

Lastly, my Gaui wants to run all over the place, and I'm sure that my swash is as level as it's going to get. I dial in some trim, and then it starts to go the other way, and the directions that it's drifts constantly changes. Could the above vibration problems cause this? I'm sort of stuck because I've haven't crashed my Gaui, although I haven't flown it in a while. I was really careful building this thing, so I'm really stumped. Thanks.

[choppersuey]

Check for bent main shaft


also take your heli to a silent area and slowly turn the main gear (no power) listen carefully for a squeak like sound. if you hear it stop and look very closely at the belt , is there any fraying on its edge? if so time to change belt soon if not now. and if so also check gear and tail Cog to see if it is damaging the belt. also you might have had belt to tight.

on tail check to make sure tail output shaft is not bent as well.


Hope helps.
sometimes main shaft so slightly bent you have to pull it and roll on something very flat like a thick piece of glass , also have light shining from behind or a white back ground so you can see the tiny gap as you roll it if it is bent. I just pulled one that was slightly off I put a dial gauge on it and it was only .0006" bent. but the roll test showed it much better. a brand new one should be perfect . but i would check new one before putting back together.

use a mag glass and check over things slowly carefully.

REEDIT
read over your post again you mention verticle head movement.
Check collars on main shaft small on very bottom and large in center (between gear and bearing) make sure set screw is there and secure. also try to move shaft up and down manualy and look at each bearing. make sure they are ok and seated properly.

control problem is related I think.

[J-Heli]

Could the pinion gear mesh being to close to the main gear cause a vibration in the tail?

[stoatnchips]

A badly moulded main gear, coupled with a tight pinion mesh could cause vibration. The 2 gears i have tried both have a wobble on them and a very slightly eccentric. Choppersuey has got some good ideas, i find rolling the main shaft on a mirror helps as it doubles the visual 'wobble'.... just have to brush the Heli crack to one side first ;)

[J-Heli]

.... just have to brush the Heli crack to one side first ;)

lol :rolling

My main gear is definitely eccentric and poorly moulded and my pinion to main gear mesh was bad, so that's what I think the problem is because I don't see anything that's bent, damaged, etc. Should I get a new main gear, or just readjust the pinion to main gear mesh? Thanks again.