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HomeAircraftHelicopterGasser Model RC HelicoptersOther › Severe wag on Predator
03-10-2010 09:40 PM  8 years agoPost 1
flyinfriend

rrApprentice

North American continent

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Hi,

I have just started flying my Predator gasser with a g231 and it has a severe tail wag. It doesn't seem like a wag related to running rich and four stroking. I don't want to lean the engine out anymore than it is. I am using a Futaba gy401 and 9253 servo. With the gain down to 75% (in my radio > 50% is the point where HH mode kicks in) that it will swing almost 90 degrees. As I increase the gain the arc becomes smaller and at 100% it is still wagging but in a smaller arc. This is not a crazy fast wag or a kick. I switched out to another 401 I had on a great flying bird and I have the same issue so it is not a damaged gyro or servo. I tried mounting the gyro on 2 pieces and one piece of tape, no difference in the wag. I tried moving the ball out on the arm and in on the arm, no difference.

My last thing to attack is replacing the tail hub. When I assembled the tail grips I noticed one side when rotating the grips had a slight bind. However I mounted the tail so the grips where on the rotational side that turned freely. The control rod/tail movement is free and easy as it is now.

I tired to fly it out of HH in normal mode and it is just too difficult (incredibly sensitive) to fly for an extended period in non-HH mode.

If anyone has any other suggestions I would greatly appreciate them as I am running out of things to check.

Thank you,

Tom

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03-10-2010 09:58 PM  8 years agoPost 2
AceBird

rrElite Veteran

Utica, NY USA

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When I assembled the tail grips I noticed one side when rotating the grips had a slight bind. However I mounted the tail so the grips where on the rotational side that turned freely.
A bind is never a good thing.

sorry to come at you with a bunch of questions but unless you describe something that is normal there is no easy answer.

is this a new problem
what headspeed, gear ratio and blades
what throws are you getting
any noise in the gears, crown and bevel

close up photos help if they are not blurred.

Ace
What could be more fun?

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03-10-2010 10:55 PM  8 years agoPost 3
rotaryfalcon

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S.E. USA

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Hi Tom, make sure the pitch control arm is not binding on the tail case. It took two small washers(and a longer bolt) to clear on my Predy. Also I had to slightly enlarge the rod guides as there was quite a bit of binding. Using the supplied srevo mount the rod comes very close to the boom, check there for contact. I spent almost as much time working out the kinks in the tail than the rest of the build. Using a 401 and a 9254 my tail has been rock soild from the get go.

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03-11-2010 12:42 AM  8 years agoPost 4
oldfart

rrProfessor

Vancouver, Canada

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How have you isolated the gyro from the vibrations?

With the 401, I found using two layers with an isolator in between them (like on the 601/611) can make a big difference in a gasser.

But I would be more inclined to bet it is in the tail rotor assembly.

Be sure you have assembled the tail blade grips with the bearings and spacers in the proper sequence. If you have forgotten to put the small M5x7x0.5 spacer that fits between the thrust bearing plate and the radial bearing or have installed it in the wrong sequence, this will cause binding when the tail rotor is at speed. You would not be able to feel this binding on the bench - ditto if one of the thrust bearing plates is assembled in the wrong sequence.

Phil

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03-11-2010 02:20 AM  8 years agoPost 5
rotaryfalcon

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S.E. USA

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The spacers for the thrust bearings shipped with my kit were of the wrong thickness. When installed they caused pretty severe binding. You might want to check them.

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03-11-2010 02:58 AM  8 years agoPost 6
4 stroke flyer

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Dowagiac,MI

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If you have the tail slider smooth as glass and no binding in the control rod. I would put money on vibration. I fought a tail wagging problem on my gasser most of last year. I went through everything imaginable trying to prove it was something other than vibration. turns out vibration was the culprit. good luck.

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03-11-2010 03:08 AM  8 years agoPost 7
Helizrule

rrVeteran

Lake Ariel, PA

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My original Predator tail grips also had binding problems and I replaced the whole assembly with Raptor 903D parts. Much better now. I am sure there is a fix but that's what I did and never looked back.

One mile of road will take you one mile. One mile of runway will take you anywhere in the world.

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03-11-2010 03:19 AM  8 years agoPost 8
jschenck

rrProfessor

La Vista, NE.

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how far out is the ball link on your tail servo? maybe too far and causing too much mechanical gain?

I agree with above comments about looking for drag with the push rod in the guides and against the tail case. I also had both of those and had to work the assembly over until it works smooth and with a reasonably low amount of drag in the controls. disconnect the push rod at the servo and try moving the controls by hand and see if it feels smooth and low effort.

And if the thrust bearings are not right in the grips that'd be a strong contender for the problem.

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03-11-2010 01:46 PM  8 years agoPost 9
kogibankole

rrKey Veteran

albuquerque/ibadan

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is your tranny smooth?
Bill me covered the auto hub mod. Have you done this? Do you have all the gears complete? No teeth missing?

What is the nature of the vibration? Is it side to side or up to down movement?

if im not blade bogging youll find me pack puffing

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03-11-2010 01:46 PM  8 years agoPost 10
rotaryfalcon

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S.E. USA

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If it starts to beat you too bad, a Trex tail with a Rappy slider fork works beautifully.

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03-11-2010 02:11 PM  8 years agoPost 11
flyinfriend

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North American continent

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Thank you all for the input. I removed the tail hub last night and it was not completely smooth turning. However when it was all mounted the movement of the control rod moving the tail was not binding at all. the grip had felt better when I first put it on during initial assembly. The bearings were all in correctly and the little shim installed in the right order. I took another new hub and tried assembling one grip. I can't seem to get the little shim to seat easily/properly. It is a really tight fit over the hub axle. I thought this might have been my initial problem but was able to get the grips to turn smoothly on the half turn side that mattered when mounted. I am guessing that binding was occurring once the tail got up to speed. When I took the tail hub off the binding was worse then when I installed it originally.

How do you get that little shim to seat properly when it is such a tight fit?

The tranny is very smooth.

I had also tried moving the ball on the tail servo in and out, resetting the limit and it made no difference in the wag.

thanks again for all your help,

Tom

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03-11-2010 02:44 PM  8 years agoPost 12
rotaryfalcon

rrApprentice

S.E. USA

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If you got the same shims I got they have to be wrong. On the many different helis I have built these shims ate very thin and appear machined or ground. What was with my heli(I believe our kits are the same vintage)were two stamped washers, with a thickness that required the grip retaining nuts to be left loose to get proper clearence to allow the grip to rotate freely. This required the nuts to be loctited not something I doing. If you have sorta gold colored stamped, rounded washers, Im sure they dont belong in the tail.

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03-11-2010 03:42 PM  8 years agoPost 13
flyinfriend

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North American continent

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Severe Tail wag on Predator
Thanks rotaryfalcon for that reply. I believe I do have the same washer as you (gold in color and slightly rounded or stamped). I also found that I couldn't tighten the locknuts down completely without binding. I also find it almost impossible to get the shims down the hub axle properly, the fit is incredibly tight.

I have emailed Paul at Century to see what he thinks. He has been very helpful with all the issues I have had with this kit.

Thanks again,

Tom

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03-11-2010 03:48 PM  8 years agoPost 14
rotaryfalcon

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S.E. USA

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All is not lost, as these washers make excellent spacers to lower the pitch slider arm to get some extra clearence with the tail case. Use a longer bolt with a nut. I just didnt trust the plastic only threads for the pitch arm pivot bolt.

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03-11-2010 04:12 PM  8 years agoPost 15
Billme

rrElite Veteran

MS

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I'm still flying 5 year old kits, so I suspect rotoryfalcon may be correct with this problem..This is hard for me to keep up with if Century changes something this small..

Good job Rotoryfalcon

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03-12-2010 02:21 AM  8 years agoPost 16
flyinfriend

rrApprentice

North American continent

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Hi,

I looked up the washer on Century's site it is part cnlr1003. It looks like the part I have. It is a gold stamped washer. However mine does not fit well over the axle of the tail hub. I'm still waiting to hear from Paul at Century.

http://www.centuryheli.com/products...3¤tid=532

Thanks,

Tom

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03-12-2010 02:41 AM  8 years agoPost 17
rotaryfalcon

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S.E. USA

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Yep, those are the washers. The ones I got were closer to 1.0 mm thick. The hole is marginally too small also.

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03-12-2010 02:37 PM  8 years agoPost 18
flyinfriend

rrApprentice

North American continent

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Hi,

I measured the washer and it is the 3x5x.5, so mine is the right size. The fit of the washer on the hub is tight and when I first noticed the bind in the initial build I removed the shim and reassembled without and the grip turned perfectly free (obviously I didn't leave it this way and I reassembled with the shim the best I could). Not sure what is going on here but last night I assembled the grip with the shim again thinking I would tighten the nut down to the point where it had to seat the washer and bearings completely and the nut never settled (stopped). So I tried removing the nut and now it does nothing but sits there and spins. It won't come off. It must have stripped and now the nylon is probably spinning within the nut. This is SOOO frustrating. I have built several heli tails without any problems. Any ideas on how to remove a stripped locknut? I could Dremel the hub at the back of the grip but it is right up against the bearing so I can't get in there.

Thanks again,

Tom

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03-12-2010 02:53 PM  8 years agoPost 19
rotaryfalcon

rrApprentice

S.E. USA

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I pulled the washers off last night and measured them again. On mine any way, if you measure the outer ring it is .5mm. If however you measure across the washer it is closer to 1.0mm. I am assuming they are conical in shape due to improper stamping. I suppose you could hammer them flat. Not something I would want to do. Looks like you have another problem now though. Sounds like the easiest approach is a new hub. I know I have probably said it enough, but the Trex tail assb. is only $15.95 complete, and is a much nicer peice.

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03-12-2010 03:02 PM  8 years agoPost 20
Billme

rrElite Veteran

MS

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Should be able to use needle nose pliers and pull on as you try to turn it...
You can't take a file and increase the id on that washer a bit..Also it seems the washer is to thick..Since it is brass, just put it on the tip of your finger, and drag over some sand paper to decrease the thickness . Forcing it want help..

Yes, its a d$% shame you have to do this on a new kit, because a part was change and not fitted correctly..

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