Feathering shaft thrust bearings.

[watdazit]

Ever since I first built my Trex 600 Pro DFC I have been concerned about the notchy feel rotating the main blade grips on the feathering shaft. I have assembled the head several times but I cannot get rid of that notchiness. It feels just like a bearing is stuffed. If I do not tighten the bolts up tight it is OK but as soon as I tighten the bolts right up the notchiness appears. I must say I have built enough helis,and repaired them to know how to put them together. Has anyone else had this problem and do you have a workaround or answer. It is almost like the feathering shaft is too short and in tightening the bolts I am binding the thrust bearings.

[nabl74]

Originally Posted by watdazit

Ever since I first built my Trex 600 Pro DFC I have been concerned about the notchy feel rotating the main blade grips on the feathering shaft. I have assembled the head several times but I cannot get rid of that notchiness. It feels just like a bearing is stuffed. If I do not tighten the bolts up tight it is OK but as soon as I tighten the bolts right up the notchiness appears. I must say I have built enough helis,and repaired them to know how to put them together. Has anyone else had this problem and do you have a workaround or answer. It is almost like the feathering shaft is too short and in tightening the bolts I am binding the thrust bearings.

nope my 600l is silky smooth.

suggest you try new thrust bearings.
if this doesnt fix it, check the length of your feathering shaft. make sure it is to spec ( could be short and causing excess compression on the thrust bearing)

also check the thrust bearings arenright way round.

with my 600l i actually had to shim the blade holders between dampers and feathering shaft collars due to feathering shaft being a touch long.

[reichly]

I've been told many times this notchyness is normal . If you pull outward in the blade grips while rotating them, as they experience in flight, the notchyness goes away.

[RC/DC_5000]

I would say that's definitely not normal and not good. Notchy bearings means they aren't smooth, they are pinched, they are going to wear out faster. They will likely fail much sooner.

Assuming you put the head together correctly- You might just have a bad bearing, even from the factory brand new.

My blade grips were notchy after a crash. I replaced all the bearings and blade grips and it went away. Totally smooth.

[watdazit]

Thanks guys for the suggestions. I think my first step will be to try another feathering shaft as it has the appearance the shaft, or at least the end where the thrust bearings are, is short and tightening the end bolts is pinching the bearings. Pulling on the blade grips does not make a difference. The bearings are installed the correct way. In fact I reversed the order of the thrust bearings to see if there was a difference, which there wasn't.

[watdazit]

On ordering the new feathering shaft it appears they have been revised.

600 Feathering Shaft Set H60H002XX AUD$15.40 (in stocks)
http://www.wattsuprc.com.au/goods.php?id=1872

Align have done away with the 6mm diameter ends and now then shaft is 8mm all the way. This should alleviate the problem.

[cobieg]

Align have done away with the 6mm diameter ends and now then shaft is 8mm all the way. This should alleviate the problem.
[/QUOTE]

It is the shaft for the Dominator. I just put one in my 600 pro stretch project. I like that it uses a bigger screw to hold the blade grip on.

[Smoggie]

The new shaft with 8mm ends and larger thrust bearings and bolts was fitted to the later 600 Pros, and carried over to the Dominator.

The notchiness is not the thrust bearings, it's caused by axial pre-load on the inner radial bearings. The pre-load in turn is caused by the dampers (have you maybe fitted different dampers?).
If you are going to swap a bearing swap the inner radials. Some heads have shim washers to adjust the bearing pre-load, removing the washer or fitting a thinner one will reduce pre-load.

[watdazit]

Thanks Grumpy Old Man. I would have thought the rubber dampeners would have cushioned any side load on the inner radial bearings but I accept what you are saying makes sense for the outer radial bearing. However for an axial load wouldn't you have to have the centre of the race being pushed one way and the outer pushed the other. Does this happen? I might experiment and leave the thin washer out between the thrust bearing and outer radial bearing. I have a stock of shim washers but I am not sure if I have any with the correct ID and OD.

(We may be at cross purposes with inner and outer radial bearings. I would call the one nearest to the head the inner.)

[Smoggie]

Yes, the inner one is the one nearest the head block.

That bearing gets loaded axially because the damper rubber gets squeezed and so pushes outward on the bearing's inner race. The blade grip pulled in by the feathering shaft pushes inward on the bearing's outer race.. Hence these two opposing forces cause the inner radial bearing to see a large axial load for which it's not designed and it gets notchy.

Putting in different dampers that are slightly larger in volume but softer makes them 'squeeze' outward more so this increases axial load dramatically. The standard Align ones are rock hard so don't squeeze out at all.
Removing the washer on the other hand allows the blade grip to move outward slightly reducing the squeeze.

I know it does appear counter intuitive at first, but trust me on it....

[watdazit]

I fitted the new Align replacement 8mm "Dominator" shaft and the problem was fixed. It's as smooth as a babies posterior now.