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HelicopterMain Discussion › Vibration..only when add collective
04-09-2011 02:20 PM  6 years agoPost 1
StevieM

rrNovice

Surrey UK

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Folks,

Realise there are many things that can cause vibration, but was wondering what my issue is.
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Eco 8.....just added hotter motor for higher headspeed.
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What is happening, is that as I am spooling up for the 1st time for a flight,(creating excessive RPM at mid stick...you know, this is only while ESC has not seen full max throttle stick position, yet thinks say 70% is full, so hasn't scaled itself properly at this stage as stick not reached full limit), the blades will reach approx 2000 as I go through maybe 0-4deg pitch, and all is really smooth...no vibration at all.
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If further add collective through hovering pitch to 9deg, the rpm will drop to 1700, but a fair degree of low speed vibration kicks in (skids/t-boom/canopy etc) for this down to hover pitch.
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Tracking at hover pitch looks fine....both blades exactly in line as far as can tell.
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So....I am puzzled as to how all is smooth throughout the whole rpm range with not much load, but vibration creeps in as pitch increased past approx 5deg., despite tracking good.
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With previous set-up/motor, hovering was much smoother at the lower RPM of 1500.
Any ideas, please shout.
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Many tks, Steve

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04-09-2011 02:42 PM  6 years agoPost 2
Heli-on

rrVeteran

Southern Cali, CA - USA

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I'm not familiar with the heli you're talking about.

If you're tracking is dead on through the entire range, I guess you can rule out notchy grip arm bearings.

If all you did was swap motors, I'd have to suspect something with it. Possible bad bearings or impromperly balanced outrunner case?

Wouldn't hurt to double check things in the head for balance. Especially the flybar - if it has one.

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04-09-2011 05:28 PM  6 years agoPost 3
uglyrider0078

rrApprentice

Natick, MA

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Vibration..only when add collective

check out this tread
https://rc.runryder.com/helicopter/t636657p1/

Team Miniature Aircraft

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04-10-2011 10:34 AM  6 years agoPost 4
StevieM

rrNovice

Surrey UK

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Got a feeling that maybe 1700 is the resonant "sweet spot", and when spooling up I am not staying in this area long enough for the shakes to start.
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Despite balancing blades by hanging from thread, using bolt through the 'oles, have ordered proper balancer from HK.
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Will also dial chk shaft, and use my high point Dubro balancer to chk shaft/head/flybar as a whole (guess will need to remove swash and all links to do this, just leaving head/grips/seesaw/flybar, as the ali swash c of g is not at its centre)...I suppose if I add the blades I will need to ensure they are absolutely in line, and pulled hard away from shaft.
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I realise that this will not place them in their "in-flight" lead/lag positions, but will do my best.
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Tks for the advice/link
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Steve

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04-11-2011 05:39 PM  6 years agoPost 5
Heli-on

rrVeteran

Southern Cali, CA - USA

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Best way to balance things is with a digital gram scale that has .01/gram accuracy. Then you can truly balance the individual components of the head that will matter the most - like grip arms and flybar paddles.

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04-12-2011 05:40 PM  6 years agoPost 6
StevieM

rrNovice

Surrey UK

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Tks for that...will try to source some 0.01g scales also.
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Meanwhile.....
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Removed blades earlier, and spooled up flybar slowly through to 2200rpm.
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Absolutely smooth throughout whole RPM range, with no hint of any vibration at all.
While doing this, also checked flybar tracking...all fine.
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Guess that proves head generally OK.
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Removed feathering shaft..this had a very small bend in it, just noticeable when rolled over a mirror....stuck it in my drill press and patiently gave it some light taps with hammer...better now.
(can a marginally bent feathering shaft really cause vibration??)
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Will clean/re-grease my thrust bearings, while all in bits/re-test, then, if no change, balance head with blades on hi-point.
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Tks for your interest...will post resolution if (when) get there.
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Rgds, Steve
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04-12-2011 05:47 PM  6 years agoPost 7
Ronald Thomas

rrMaster

Gainesville, Fl, USA

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Also check to see if the main shaft bearings are slipping in the block

Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!

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04-12-2011 07:13 PM  6 years agoPost 8
BeltFedBrowning

rrKey Veteran

Kansas City

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Is this a stock plastic head? Have you added any thrust bearings to the main blade grips? The Eco8 does not have thrust bearings stock.

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04-13-2011 12:54 PM  6 years agoPost 9
StevieM

rrNovice

Surrey UK

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Stock plastic head/grips.
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Added thrust bearings a few years ago (correct kit, with the T end nuts, inner/outer races slightly different ID's etc...fxaeromodels?...sourced some for the tail locally in the UK).
Just re-assembled....forgot what a pain it was trying to lubricate all + sandwich everything back in the correct order ,without getting any grease on the final end thread so the threadlock will do its job!
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I will dial indicate the mainshaft, and when the following arrives (it's only cheap, but looks like it's been CNC'd, and has bearings...will be better than the "bolt throug blades and thread" method I've been using, although cannot tell if should clamp blades above or below the blue plate):-
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http://www.hobbyking.com/hobbyking/...idProduct=12240
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Will chk all before running up next.
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Tied self in knots last night reading various RR posts debating whether to chk shaft/head/blades on high point or not....seemed to focus on grey area of the fact that you would never really be able to replicate the "in flight" lead/lag positions, so could make things worse.
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Enough waffling..... tks again for interest, Steve

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04-13-2011 09:47 PM  6 years agoPost 10
Leejay

rrNovice

Sussex, Uk

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Flybar cage, paddles have to flat, as you have found out. After all, the flybar changes the angle of the main blades consistently unless your in a perfect Hover, etc.

Vibe 90 3D, Trex 700E flb no gov, Rave 450 fbls , Trex 250

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05-05-2011 02:27 PM  6 years agoPost 11
StevieM

rrNovice

Surrey UK

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Next chapter

Dial-indicated main shaft....runout F.T.B. 0.07mm....managed to reduce this to 0.01mm by repeatedly tapping with hammer, bridging it between 2 bricks!! (lots of patience...at least I know it's good now, although 0.07mm is only approx 3 thou, so this really seemed small initially anyhow).
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Main blades....small amount of tape removed to balance perfectly.
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High-point....removed swash and all that could not make "symmetrical" round shaft....all fine.
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So...will re-test/advise outcome.
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Rgds, Steve

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05-21-2011 08:26 AM  6 years agoPost 12
StevieM

rrNovice

Surrey UK

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Success!!!

Absolutely rock solid now....no sign of any shake at all!!!
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Cannot tell which of the above fixed things, but really happy with the result..... what a difference!!
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I know it seems to be a time-consuming exercise, but if anyone even has any slight, annoying vibration issues, I definitely think it's worth investing in a dial indicator (really not expensive) aswell as the usual blade balancing tools.
Just just put aside some time, take it slowly....it really is worth the effort.
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Have fun,
Steve

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