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HelicopterMain Discussion › What all could be the cause of tail wag now that​wasn't there before ?
04-01-2017 04:33 AM  7 months agoPost 41
EEngineer

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TX

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"Lots of capacitors in there."

Especially within the PS....

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04-01-2017 06:24 AM  7 months agoPost 42
joshreynolds777

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Willis, Tx

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I remembered the original owner had some little bitty tiny tail blades on that thing. They were covered in grass stains and looked cheap. So I chunked them before I even flew it.

The gain was at 75%. I dropped it to 65%. And no change. I'm gonna go down to 45% gain and try that. The tail blades I have on it are not in bad shape. Only slightly knicked. Or however you spell it.

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04-01-2017 07:38 AM  7 months agoPost 43
heliraptor10

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kokomo, in-US

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You've said you checked the pushrod for binding?

Another thing you can do is to remove your main blades and strap her to your bench. Disconnect the push rod from the servo and spool it up to a lower rpm. Manually operate the tail with the push rod.

Sometimes the binding isn't actually in the rod or guides, so you can only identify the binding by checking it in operation.

If it is binding when running but not otherwise then it's the tail mechanics.
Bearings
Bushing on the slider

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

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04-01-2017 01:55 PM  7 months agoPost 44
joshreynolds777

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Willis, Tx

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I might sell the t500. Or stuck it at the lhs on consignment and use the lipos I have for it on a goblin380 BNF they've got up there. Anyone instereted in a trex500 FBL for $250 ? It's got the 6 axis self level gyro on it I don't use

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04-01-2017 05:47 PM  7 months agoPost 45
EEngineer

rrProfessor

TX

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"Manually operate the tail with the push rod."

This is also a good way to check for the "tennis racket" effect.

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04-01-2017 06:13 PM  7 months agoPost 46
heliraptor10

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kokomo, in-US

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"tennis racket" effect

That's a new one. Or a really old one. Not sure if it rung a bell in my head, or if that was just tinnitus.

What's the tennis racket effect?

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

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04-01-2017 06:16 PM  7 months agoPost 47
JuanRodriguez

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The Villages,​Florida

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I believe it's when you stop the tail abruptly and it bounces back a little in the opposite direction

Been there, done that and old enough to know better.....

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04-01-2017 06:18 PM  7 months agoPost 48
heliraptor10

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kokomo, in-US

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Don't give up Josh.

Sometimes the harder it is to get a Heli tuned right the more satisfying it is when you solve it.

Some of my most satisfied flights had nothing to do with mastering a new stunt, instead they were just awesome because I nailed a long time issue.

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

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04-01-2017 06:19 PM  7 months agoPost 49
heliraptor10

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kokomo, in-US

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Lol... duh.

Thanks Juan.

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

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04-01-2017 06:22 PM  7 months agoPost 50
heliraptor10

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kokomo, in-US

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I thought the tennis racket effect was usually blamed on gyro/fbl settings?

How does a strapped in bench test reveal this?

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

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04-01-2017 06:25 PM  7 months agoPost 51
JuanRodriguez

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The Villages,​Florida

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Don't know that it can unless you fly it .... but I'm no expert ......

Been there, done that and old enough to know better.....

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04-01-2017 06:28 PM  7 months agoPost 52
heliraptor10

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kokomo, in-US

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Also Josh

If you decide to that bench test

Strap it down, through the legs and frame. (And don't forget remove the main blades) I connect the battery from outside the frame so if the unexpected happens and the heli gets free (really not likely but hey) it will disconnect the battery before causing too much damage.

PS. Does this kind of trouble shooting through the internet drive anyone else crazy? What I wouldn't give to just be able to drive around fixing helicopters...

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

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04-01-2017 06:30 PM  7 months agoPost 53
heliraptor10

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kokomo, in-US

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Yeah its hard to tell with Engineer sometimes.

Smart and a smart ass

Just kidding E!

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

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04-01-2017 06:38 PM  7 months agoPost 54
JuanRodriguez

rrProfessor

The Villages,​Florida

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I would definitely NOT RECOMMEND strapping a heli down to do "bench testing " unless you first remove the main blades first ....

Been there, done that and old enough to know better.....

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04-01-2017 06:49 PM  7 months agoPost 55
heliraptor10

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kokomo, in-US

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I said to remove the mains in my first comment about the test

But I fixed it,
Just in case anyone else is going over this and misses it.

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

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04-01-2017 09:38 PM  7 months agoPost 56
EEngineer

rrProfessor

TX

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"What's the tennis racket effect?"

Come on.....no April "fooing" around....

What you describe as "push-rod binding" is a perfect, empirical demonstration of "the tennis racket effect" on tail rotor pitch deflection.

A guy made a business out of "quantifying" this effect and crafting counterbalancing tail blade bolts to minimize this effect....using mechanical test instrumentation.

He was a mechanical engineer.....and a damn good one....

The Tennis Racket Effect(with regards to the tail rotor):

The servo has to overcome any "binding" by the push-rod guide, the tail pitch tiller arm, etc......very true, as mentioned.

But....in addition, with the geometry of the rotating tail rotor(rate = ~ 4.5 to 5 times that of the main blades), it requires even more servo torque to also deflect the pitch of the tail blades....

Assume there is absolutely no binding......there is still the above condition when +/- tail pitch is applied.

Don't know who invented the term, but if one used a "tennis racket" and spun it like a tail blade, it would try to return to "0 pitch"....west coast thing, I guess....

No matter what....it's easy to demonstrate....on the bench....

1) Remove main blades, leave tail blades on.
2) Clamp the heli to the bench.
3) Remove tail push-rod from servo end.
4) Did I mention to clear the test area? The tail will blow a "gail"....

5) Spool up....gently.
6) Try to deflect the tail push-rod....feel the force required.

The MechE used a force meter connected to a computer to measure the push/pull force for accuracy.

Feeling is close enough for us.

The solution was to add tail blade bolts that "stuck out" a bit...and that slight weight...spinning at such a high rate...would counter the force required to deflect the tail blade pitch.

The MechE made "calibrated" tail bolts for many makes/models of tail rotors.

All we can to is add small washers...different bolt heads, etc....to cause a "moment arm" to do the same thing.

By repeating the above bench test, you can feel the force to deflect the tail blade pitch lessen....

The result is that the tail servo can perform to it's optimum.

FWIW

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04-01-2017 09:49 PM  7 months agoPost 57
EEngineer

rrProfessor

TX

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Keep in mind that this was perhaps 10 or so years ago, when servos weren't what they are now.

A fast servo had minimal torque....digitals were just coming out.

With today's digital servos, this isn't much of a problem anymore.

But, the effect is still present....

It's a great "lab curiosity" that you can amaze your friends with.

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04-02-2017 02:17 AM  7 months agoPost 58
heliraptor10

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kokomo, in-US

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I well remember the "Chinese weight mod"

Some helis still have tail blades grips that have this built in.

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

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04-02-2017 04:24 AM  7 months agoPost 59
EEngineer

rrProfessor

TX

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Same thing....different name....lmao

Then you must remember Magic Rotor Spray....

Watch at YouTube

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04-02-2017 04:45 AM  7 months agoPost 60
joshreynolds777

rrApprentice

Willis, Tx

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It looks like I've got it knocked out. I got the gain all the way from 65% down to 45% and a new set of tail blades and the wag has finally stopped. The original owners blades must have had WAY less surface area. It's what I guess I can attribute this to Anyway.... Tail gain too high with bigger tail blades that were on there at set up. Tail authority seems perfectly fine for the time being. Did some fff. Some fast backward flight. Hard turns. And heavy climb outs just out front of the house. No room for much more. Only wag seeemses to be during normal throttle mode climb outs. The wag wasn't there during idle up climb outs. I guess I can attribute this to the power surge at lower head speed ?

There is still a slight bobble, an up and down tail bobble that's bothering me some, the whole bird moves with this bobble slightly, it's not just the tail. but the really bad buzz saw wag is gone thank goodness. That bobbing is pretty annoying. But it's fairly slight and not bothering me a whole lot. With that being said, what's that usually mean ? Main blades un balanced ?

I checked the tail out well . Everything seems very tight.

Try it with higher head speed and see if it levels out ?

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HelicopterMain Discussion › What all could be the cause of tail wag now that​wasn't there before ?
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