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T-REX 250 › Back with 250SE tail wag....
04-21-2011 01:11 AM  7 years agoPost 121
foodman392003

rrApprentice

Motorcity,Hockeytown ,USA

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HarveyR,
Thanks once again for the advice. I'm very close and thats a good point about heating up. It is a very fun little heli and it is flyable now so I'm happy and with alittle tweeking I'm sure I can get it perfect. I keep this topic saved and check up on it regulerlly. Have a great summer flying I know I will.

Compass Chronos,7HVU,6HVU

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04-21-2011 02:25 AM  7 years agoPost 122
Safe_Cracker

rrKey Veteran

Chicago, IL

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There has to be a common element in this dreaded tail wag. I have one 250 that wags and another that does not. I have a 450se that has a slight wag and a pro that is ROCK solid. I am leading towards bad vibes and/or tail belt. Honestly I think it is high frequency vibes so probably tail rotor...

Polo

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04-22-2011 04:10 AM  7 years agoPost 123
heliraptor10

rrKey Veteran

kokomo, in-US

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HarveyR,

Yeah my tail operation is smooth at flight RPM.

Its down to Vibes,
cuz the gy520 seriously improved the tails hold, but it still has the same general wagging problem.

My main bearings actually have a sort of "grinding" feel, just rotating the main shaft inside. I got my Rex used, so who knows how many crashes it had before I got it.

So I am trying the bearings first.

Then the head....

SafeCracker,
I am also wondering about my tail (vibes). How do you balance this tail?

Goblin! where have you been all my life?
RC helis, the original fidget spinners

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04-22-2011 08:52 AM  7 years agoPost 124
HarveyR

rrVeteran

France - North

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I've never been so convinced about the vibs issue, mainly I suppose because I've never experienced it.

I've had terrible helies (NP in particular, with high vibrations) with gyros mounted with simple tape (and additional straps often) without any foam and this never caused issues.

Many times I've mounted gyros (401, 750, ...) with any old tape and any old straps around them (and touching wires and frames and the lot) and none of this ever seemed to cause a problem.

Also, on my 250SE, when the tail wag issue appeared, I tested all sorts of locations/tapes for the gyro and it simply didn't change anything at all.

I know this doesn't sound right as in all gyro manuals they insist on using their foam and avoiding contact with wires/frame etc. It's just my 20 years experience has never shown this to be of any importance at all.

I'd say if it's a vib problem, surely it should change by one of the following:

- messing with the foam/tape (no foam, loads of foam)
- moving the gyro around the heli (vibs are different all over the heli)
- bind a little piece of led (a few grams should do) to the heli or gyro to modify modale frequencies (reasonance)
- change HS, this will also greatly change nature of vibration
- slightly change tracking (half a turn)
- slightly change paddle distance
- ...

I'd say if none of this has effect, than it isn't a vib problem.

Just my thoughts, however the way, I hope you get it working, and tell us what it was! good luck!

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04-22-2011 06:31 PM  7 years agoPost 125
heliraptor10

rrKey Veteran

kokomo, in-US

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Thats the problem,
all of those things do make a difference for most of us, yet nothing fixes it.

The reason I am convinced that it is vibes is because of the 250's HS. A lot of people have good luck lowering it. And come on, 4000rpm? It is a small bird so the vibrations are not intense. So those of us coming from bigger birds, see or feel the little zzzzzz goin through the frame, and we think "my gyro can deal with that, it has before."
Yet, vibration intensity is only part of the story. The intensity is reduced by the small size, but the frequency of vibrations is doubled by the insane Headspeed.

I am all but certain it is my main bearings, it had at least a couple crackups before I bought her, and rolling just the main shaft feels crunchy. I disconnected the tail belt and spun her up and I still have the vibrations (hand held).

The 520 changes the LED color based on its response action, so when the vibration starts the LED flashes between the two colors.

edit: of course I thought I had a really good reason for thinking I knew the problem last time......

Goblin! where have you been all my life?
RC helis, the original fidget spinners

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04-22-2011 09:47 PM  7 years agoPost 126
HarveyR

rrVeteran

France - North

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Well, keep us informed as do what happens after changing the main bearing. One day someone could go through this whole thread (and the others like it) and attempt to create a diagnostic/resolution tree which could go through all the ideas here!

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04-22-2011 10:21 PM  7 years agoPost 127
heliraptor10

rrKey Veteran

kokomo, in-US

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Over on HF,
there are several different threads for this issue.

But the main one,
beginning with a statement from Bert Kammerer,
is currently at 26 pages!

Goblin! where have you been all my life?
RC helis, the original fidget spinners

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05-01-2011 03:28 AM  7 years agoPost 128
heliraptor10

rrKey Veteran

kokomo, in-US

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Got my bearings replaced. It did not seem to make a difference, at first. But then I started moving the gyro around different places. Where before this had no affect, now it made an improvement. Closest to the main shaft was best.

After more bench tests I noticed that when the vibes happen and the tail starts wagging that the blades are out of track for that spot on the throttle curve.
The flybar seesaw was slightly deformed in the crash.
I have noted this on my belt cp oh so long ago. When this would happen your blades would be out of track at certain points on the throttle curve, and the heli would fly poorly. But at the belt's head speed it would not induce any serious vibes being out of track.

This is not true with the Trex 250. When the blades become even slightly off track (on mine at least) enough vibration happens to disturb my gyro (futaba gy520).

So I have gotten all that sorted, but I still seem to have a slight vibe. The tail is holding maybe around 90% of where I would like it. Trying to come up with a way to balance the blades. Can't buy one right yet, no toy budget for awhile.
I have also heard of some people having luck with the usb programmer on the 520.

Goblin! where have you been all my life?
RC helis, the original fidget spinners

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05-03-2011 09:50 PM  7 years agoPost 129
heliraptor10

rrKey Veteran

kokomo, in-US

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Does anyone have any clue,
What would make the blades out of track:
At the rear of the blade disk only?

I can not come up with any explanation why the blades would track at the front of the heli, and not at the rear.

No matter how I adjust them,
I get it perfect in the front and then at the rear they are like 1-2mm off near neutral on the collective, and when they "separate" is when my tail starts to vibe.

I have the head as slop free as I can get it without buying parts,
putting in an extra washer here and there.

Goblin! where have you been all my life?
RC helis, the original fidget spinners

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05-03-2011 10:56 PM  7 years agoPost 130
Safe_Cracker

rrKey Veteran

Chicago, IL

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If you are using CF or composite blades and had a strike, it is possible the materials are separating at speed causing tracking issues. Try a different set of blades.. Polo

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05-04-2011 01:05 AM  7 years agoPost 131
heliraptor10

rrKey Veteran

kokomo, in-US

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Yeah I do have cf blades,
but they weren't part of my last crash.

I had a thought and I disconnected the tail belt again. And guess what?
The blades tracked fine, everywhere on the disc.
Reconnected and boom, there the problem was again.

My best guess is that I have a imperceptibly bent tail shaft, causing a harmonic interaction.

So that is on the order list.

I know helicopters are a trouble shooting night mare......but this one.....sheeeeeesh.

Goblin! where have you been all my life?
RC helis, the original fidget spinners

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05-04-2011 02:43 AM  7 years agoPost 132
Safe_Cracker

rrKey Veteran

Chicago, IL

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They are a royal PITA and from what I have found that everytime I pull a tail shaft out of the package (both 250 and 450) I have to check the runout because quite a few has been waaay off... Before you put the tail rotor on spin the shaft in the housing see if you can sight the shaft's runout. Polo

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05-04-2011 02:57 AM  7 years agoPost 133
jbdww

rrElite Veteran

Round Rock, Texas

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One thing that seems to help, is make sure your head speed is withing spec. I had a 16 tooth pinion on my scorpion motor, and I had the bad wag, and when I put the 15 tooth pinion back in, the wag went away.

Skids Up
http://www.jbdww.com
http://twitter.com/jbdww/

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05-04-2011 04:14 AM  7 years agoPost 134
heliraptor10

rrKey Veteran

kokomo, in-US

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Safecracker,
What's runout?

jbdww Yeah, I have the 16t pinion.

I had thought about that(me having gotten a 16 where most choose 15),
and I put the heli in throttle hold,
and went into the settings slowly bumping it up to see at what point the vibe started.
38%
So, the 15t will help but I have other problems.

Goblin! where have you been all my life?
RC helis, the original fidget spinners

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05-06-2011 10:10 AM  7 years agoPost 135
HarveyR

rrVeteran

France - North

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I'm curious to know how you're testing for vibes and harmonics on the bench? Because of course the vibration modes will be highly infkuenced by the fact the heli isn't really in the air flying? Do you maintain the heli in place with a soft and light (foam or something) fixation/support?

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05-06-2011 10:08 PM  7 years agoPost 136
heliraptor10

rrKey Veteran

kokomo, in-US

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Well its not smart,
but I was hand holding her.

My tail is causing so much vibration that the vertical fin is vibing and
even more concerning is it makes my blade disk out of track on the rear of the bird. I have verified this is the cause because without the tail belt hooked up my blades track.

So this (plus the intermittence of mine and many others problems) makes me think it is the harmonic interaction of vibes from the main drive and tail drive.

I hope to get ahold of a new tail shaft soon so that I can eliminate that as the cause.

It has been so close to perfect a couple of times now,
and I really love this bird....
I think I may do a re-kit and see if that solves it...
(mine was used )

Goblin! where have you been all my life?
RC helis, the original fidget spinners

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05-09-2011 06:08 AM  7 years agoPost 137
Safe_Cracker

rrKey Veteran

Chicago, IL

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Simply put, runout would be the amount the shaft is untrue. Normally you would put a shaft in a set V blocks and use a dial indicator to tell you the amount that it is off but in this case it may be impractical. I can usually removed the tail rotor and spin it up then look for the wobble at the tip. Any visible wobble will get magnified into a high frequency vibration with the tail all together.

Polo

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05-11-2011 11:20 PM  7 years agoPost 138
heliraptor10

rrKey Veteran

kokomo, in-US

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Safecracker,
thanks thats good to know.

I replaced everything that spins on the tail
bearings
tail shaft
main hub
blade grips

Now my vertical fin no longer vibes, but the tail is still wagging occasionally.

With the gy520 it is holding really well despite this, and I can do backwards flight (about the hardest test I can put the gyro to).

But after all of this time and money invested it should be perfect.

I switched out the bearings in the flybar seesaw and that took out the slop which improved tracking and my tail wag. I flipped the head so that the blade grips are actuated on the leading edge (flip grips and seesaw) this erased all tracking problems and didn't hurt my "pop"

But the wag is still there,
at this point it is reduced to a tiny wiggle,
but it should be perfect!

Goblin! where have you been all my life?
RC helis, the original fidget spinners

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11-03-2011 06:46 PM  6 years agoPost 139
heliraptor10

rrKey Veteran

kokomo, in-US

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Finally

Watch at YouTube

Goblin! where have you been all my life?
RC helis, the original fidget spinners

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11-03-2011 06:59 PM  6 years agoPost 140
jbdww

rrElite Veteran

Round Rock, Texas

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What fixed if for you?

Skids Up
http://www.jbdww.com
http://twitter.com/jbdww/

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T-REX 250 › Back with 250SE tail wag....
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