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Tarot Flybarless 450 Main Rotor Head


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Burgess
Extreme 3D
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Joined: 27 Mar 2012
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Location: Wales

PostPosted: Thu Jun 16, 2016 8:32 pm
PostPost subject: Tarot Flybarless 450 Main Rotor Head
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Just received a Tarot flybarless main rotor head very nice finish, but the bearings are rubbish the very slight clearances inner race to feathering shaft and within the bearings translates to way too much perpendicular movement at the blade tips and that results in vibrations.

Part of the problem being these miniature ball-raced radial bearing are produced with expansion tolerances for high speed operation and of course that not the case with blade holders on feathering shafts.
The low ball-count is great for low friction running while that's OK for vibration-free operation, with our RC electric helis we end-up with cogging bearings and increase in vibrations.

I've often thought of replacing ball-raced bearings in blade holders with bush bearings.

Setting the pitch I use two pitch gauges set each to the same angle and sight across the tops...but having to keep swapping specks maybe it's time to invest in a digital gauge.









Burgess
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tombo242
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Location: Santo Estêvão, East Algarve, Portugal. Now 82, but still feels 22.

PostPosted: Fri Jun 17, 2016 4:53 am
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Like the idea of bush bearings on the feathering shaft Burgess, as you say there shouldn't be a problem with heat or continuous speed up there. Will need some careful machining though - well beyond my power drill Laughing

Two pitch gauges are a great idea Burgess, if those blades don't track, there has to be a twist in there somewhere!

Tom.
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Burgess
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PostPosted: Sat Jun 25, 2016 12:18 am
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Tracking: another cause of tracking problems that of low spec radial bearings again.
The feathering shaft has no step-down at the ends so 4mm from end to end, with the thrust bearing in-board of the outer radial bearing. Even though the clearance is so very little it's enough to engender blade flutter in and out of track and lots of noise.
I swopped out the four radial bearings with ones that had a better inner race to feathering shaft fit, tracking close but not spot-on. So sent off for a T-rex 450 Pro feathering shaft which has no step down at the ends so 4mm right through. Also purchased a T-rex 450 Plus DFC main rotor holder set. The bearing to shaft fit almost an interference fit and means zero flutter.

These blade holders might be plastic but they have recesses for the nuts and come with shanked blade drag bolts.

The holders can accommodate an extra radial bearing, and the inner race to feathering shaft fit is superb, had to fit 1mm spacers either side of the rotor housing. Set the turnbuckles exact same length and the tracking is spot-on.

Also fitted some of these new spacer things, above and below the blade root which increase the contact area between the root and blade holder.







Plane bush bearings
4x8x3mm from here a set of 4 for £1.99
http://demonpowerproducts.co.uk/product_info.php?products_id=7165

Oil Filled Bronze Plain Bush 4x8x4mm £2.71 each
http://simplybearings.co.uk/shop/Bearings-Oil-Filled-Bronze-Bushes-Oil-Filled-Bronze-Plain-Bushes/c3_4511_4770/index.html


Burgess
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tombo242
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Location: Santo Estêvão, East Algarve, Portugal. Now 82, but still feels 22.

PostPosted: Sat Jun 25, 2016 5:11 am
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Just amazing Burgess,
As our German now ex-colleges might say "Vorsprung durch Technik" = "advancement through technology"

Amazing how bad some of the things we buy are not really engineered with the precision required to do the job. This shows just how it should be done.

Tom.
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Burgess
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PostPosted: Sat Jun 25, 2016 11:23 pm
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Perhaps the next big thing in the UK could be manufacturing the very small from high grade metals. Quality and longevity just has to be cost effective, and that's what one gets with Align components.

I'll get some bush bearings and tryout the idea, and may just extend that to replacing the main shaft bearings too. Hobbyking do main shaft bearing housings that accommodate the usual radial bearing and accommodate a thrust bearing too; so if fitted with bush bearings will increase contact area and reduce the loading and with a spot of Teflon or PTFE grease to reduce friction.
Some of the generic T-rex 450 plastic mixing arms come with bush bearings but need lots of attention to eliminate lateral lost motion. The caged ball-raced radial might be low friction but they are prone to the adverse effects of vibration due to the higher load per ball bearing in the cage.


Vorsprung durch Technik",

I wrote a short story based a play on the words, that -in short- went something to the effects of:

One year, the reindeers went on strike, well not exactly on strike but had stayed at a Himalayan ashram with dear friends during the summer vacation and refused to return to the North Pole. The elderly jesters suggested they could assist Ricky Branson to get the heavy laden sledge airborne, but Father Christmas said, "That would be virgin on the ridiculous." In the end they used four suspension springs and a flight of ducks...the four sprung duck technique.



Burgess
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tombo242
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PostPosted: Mon Jun 27, 2016 2:12 am
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Purrfect Burgess,



I just fell over laughing!

Tom.
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Burgess
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PostPosted: Mon Jul 04, 2016 8:27 am
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The bearings arrived and while a good fit for the feathering shaft, the outer diameter is greater than the blade holder housing.

Two photos:




The bushes will be OK if fitted into the plastic blade holders, but will need easing if fitted into the alloy blade holders.



Burgess
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tombo242
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PostPosted: Mon Jul 04, 2016 4:26 pm
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Looks like another delicate job in pursuit of perfection Burgess.

Tom.
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