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T-REX 450 › Tail Vibration
09-13-2007 07:00 PM  10 years agoPost 21
Boidman (RIP)

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The Home Stretch

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If you pull hard on the grips, is there the same gap between them and the hub on each side? Something thin that will just fit the space, can be twisted a little to see if it's the same for each.

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09-13-2007 08:10 PM  10 years agoPost 22
Darren Lee

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Woodstock, GA

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Yes, gap looks same. No lateral slop either.

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09-13-2007 08:50 PM  10 years agoPost 23
Boidman (RIP)

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Follow Tom's suggestion with the main blades off, to balance the tail with tape, at speed. Spin it up, watch the fin, and touch the end of the tail case with your most sensitive diddling finger. Add whatever tape you got out near the end of a blade, scotch 1/2" is kind of a standard to make the wrap with. Be sure the vibration got worse, even if you have to add more tape, before you decide it was the wrong blade.

I have seen, and others have reported here, odd behavior outside or at the fringes of logic, from slipping front or rear pulleys, on their shafts. There is enough heat at operating rpm to effect the fit of a marginal pulley to its shaft.

Grab both blades and twist them against the slop in the linkages, come up with some number or amount to compare with others.

Your old hub concerns might be legitimate, but it would be very hard to distort one, particularly without crashing. Have you ever smiled smugly while watching the tailblades pick up that purty green from grass? See if you can use a ruler to determine if both mounted grips are in line with each other. Someone already mentioned that a bent screw or hub end could be giving you grief.

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09-13-2007 09:32 PM  10 years agoPost 24
Darren Lee

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Woodstock, GA

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After some searching, I have a theory: resonance. My problem only occurs above a certain RPM, and the onset of the vibration is very sudden. Also, when it's vibrating, I can see the boom resonating up and down.

I have not checked mine, but others have reported the same problem and the culprit was loose or unglued boom supports. I'll have to check it out tonight. I do have the aluminum boom though. The CF one is supposed to be worse about resonance.

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09-13-2007 09:36 PM  10 years agoPost 25
Boidman (RIP)

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Distinct possibility, but keep in mind that a system at peace with itself will not show any issues with no supports at all.

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09-14-2007 05:43 PM  10 years agoPost 26
SSN Pru

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Taxachusetts

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Are you using a Carbon fiber boom or an aluminum one?

Stupidity can be cured. Ignorance is for life!

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09-14-2007 05:59 PM  10 years agoPost 27
Darren Lee

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Woodstock, GA

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Are you using a Carbon fiber boom or an aluminum one?
I do have the aluminum boom though. The CF one is supposed to be worse about resonance.
I did a test where I held the boom with my hand, hoping to dampen the resonance. Didn't work. Next step is replacing the hub and grips with HS1189. I also have some new tail blades coming.

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09-14-2007 06:21 PM  10 years agoPost 28
SSN Pru

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Taxachusetts

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I did a test where I held the boom with my hand, hoping to dampen the resonance
Yep, best way to rule out resonance, increase or decrease the mass.

Would have been interesting if the mass of your hand changed the natural frequency of the assembly. Try flying your trex with a mass equivalent to your hand on the tail haha .

The hunt continues...

Stupidity can be cured. Ignorance is for life!

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09-26-2007 03:12 PM  10 years agoPost 29
MoReese

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Dallas, TX

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I had tail vibration at 50% throttle and up. Vertical fin was vibrating badly. The carbon fiber boom was the culprit for me. I had aluminum boom before a crash and decided to upgrade to carbon fiber since I was fixing. I had vibration since then and just assumed something didn't get assembled correctly in the drivetrain. After many late frustrating evenings I tried swapping back to aluminum (since i tried everything else) and vibration went away. I don't know if I got bad carbon rod or what, but that was the problem for mine.

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