Trex 450 Sport tail wag PLEASE HELP!

[Roy Schnebelen]

I am experiencing bad tail wag on 2 freshly built Trex 450 sport machines. I used Finless Bob’s build videos step by step and assembled the heli’s per the manual as well. I have tried everything in the book: I have a good clean and smooth mechanical tail and linkage setup, changed out the Align 790 gyro to the Spartan Quark after viewing posts on that subject, increased head speed, checked the main rotor for out of balance parts, moved the ball link on the servo from 8mm to 5 (the tail just wags slower), changed the end point settings on the radio for the gyro gain and the rudder, and a few other things that were just plain silly trying to get this thing under control. I have adjusted the gyro gain from zero to 100%. The only thing that happens is that the was gets slower at the low setting and very fast at the high setting but never goes way and is rather violent. Any ideas? I am pulling out the little hair I have left? Oh on a side note I have a Trex 450 plus that has the exact same parts as the two 450 sports that are having the problem. I have even tried using the same settings on the J6 radio with no luck.

[matthewcornell]

It was counterintuitive but I had head issues that transmitted down into tail problems. Look for loose linkages, arms, etc. Had it had any crashes? Bent spindle, head block? Warped blades? I can dig up more detail on what i did.

[BuckAye]

Got this from the spartan site - have you tried all of these things?

Rapid wag / fluttering (continuous or during specific manoeuvres)

If the tail wag is continuous and rapid it is most likely the result of high gain. The overall gain of the tail is a combination of the gyro gain plus the mechanical gain of the tail.

Lower the gyro gain until no wag is seen at any time in flight.
In some cases you may also need to lower the mechanical gain by moving the tail servo ball link closer to the centre. See [topic 84] for information on the mechanical gain and how it affects your gyro.
The Trex 250 has excessively high mechanical gain by design. Use the shortest possible servo arm length.
For 450 size helis you may need to place the servo ball link at the shortest possible distance. If using a Futaba servo try the small servo horn disk.

[Roy Schnebelen]

I have tried moving the ball on the servo link in then tried to adjust the adjust the gain on the gyro but the wag never goes away just goes faster at higher gain and slower at lower gain. Like I said before these 2 helicopters are fresh builds with no previous use or crashes. Both are setup exactly the same but one has better performance with the gyro gain set to 100% max and the other one does better at 33%. But they both still wag. I will check linkages and head again. I used a swash plate leveling tool during head set up so I am pretty confident that the head is ok. It just seems strange to me that both helis are having the same issue after a fresh build. I have never had this problem before on my other 450 builds. Oh just checked blade tracking again and it's still dead level.

[755 robert]

Take a look at motor gear mesh (too tight or too loose)and belt tension..

[pjuran]

I am using a Align DS520 servo on the tail with the quark gyro and my 450 Sport can hover hands free. It is ROCK solid. What tail servo are u using? What raido are u using at what is your gain set at?

[Roy Schnebelen]

The mesh on the pinion and main gear has the correct about of backlash accrording to the Align manual and the tail belt isn't too tight or too loose (slipping). I am using the Align DS420 servo with the Spartan Quark gyro the gain setting on the one heli is set to 33% the other is set to 100%. Any reduction or increase to the gain setting just makes the wag faster or slower but it never goes away. I removed the flybar weights and things got a little better on both machines but still is a problem. Everything I have tried has had little or no effect on the wag.

[pjuran]

What TX are u using?

If u are using a DX6i HH mode it should be about 63 (or about 26 if you are using a DX8).

Rate mode should be anything under 50 on the DX6i and a negative on the DX8)

Make sure you're plugged into gear on the RX and that your got or +/- polarity on the servo plug into the RX and gyro going the correct direction.

[anthony1]

check the bearings in the tail blade holders by pulling on them and see if they move at all , it is possible to damage the bearing by over tightening them, also make 100% sure there is no binding in the rudder mechanism, it should move very freely ,check that the tail output shaft isn't bent, i know they are new builds but sometimes parts are bent out of the box, lastly try setting up in rate mode , not sure if it actually helps but at least you will know that you are mechanically correct,

[anthony1]

one other thing , make sure that the tail blades are moving in the correct direction, they should be moving up into the main blade wash , ie counter clockwise when viewed from the tail blade side

[chargh]

What esc are you using and are you running it in governor mode?

Sent from my X500

[mbeall]

Originally Posted by anthony1

check the bearings in the tail blade holders by pulling on them and see if they move at all , it is possible to damage the bearing by over tightening them, also make 100% sure there is no binding in the rudder mechanism, it should move very freely

this. i just corrected this problem on a 450 sport that developed the wag out of nowhere. everything moved smooth enough on the bench, but once in the air the bearings would seize

and then i damaged the replacement bearings... by over tightening. the tail was still wagging

second set i just used a little more loctite and snugged them up.

[steeleagle]

I had a tailwag on my 450 Sport converted to 3GX FBL. I had tried everything - what finally worked was lowering my headspeed which seems counterintuitive to me. If I run it at a normal throttle curve of 0-70-70-70-70 there is no wag. If I bump the TC up to 80 I get a rapid tailwag. I have reduced the rudder gain which slows it down but doesn't stop it.

Sent from my BlackBerry 9800 using Tapatalk

[Roy Schnebelen]

Ok so after all that I fouund the broblem on both helis was in the tail rotor. One of them was binding just slightly at the ent ponts and the other was a binding servo linkage. SO I guess the tail wasn't set up as perfectly as I thought. Even the slightest binding will cause your gyro to hunt.

[m5burndt]

I had a similar problem, If i turned the gyro high enough to stop the tail from drifting I would get serious wag problems. I couldnt get the gyro higher than 45% which resulted in 90 degree tail kicks when doing anything fast. I couldn't even attempt going backwards at all.

I moved the linkage ball closer in on the servo horn (drilled a new hole), redid DIR and limit setup and voila! Now I have the gyro at 80% with zero wag. When you move the linkage ball in closer, it decreases the mechanical advantage that the linkage has on the servo (short lever) and reduces the overall slop. Additionally, the servo performs better because it is using more like 90% of its travel instead of 40%.

[MtnMan1]

Originally Posted by Roy Schnebelen

Ok so after all that I fouund the broblem on both helis was in the tail rotor. One of them was binding just slightly at the ent ponts and the other was a binding servo linkage. SO I guess the tail wasn't set up as perfectly as I thought. Even the slightest binding will cause your gyro to hunt.

[vfavela]

I just finished rebuilding my trex 450 sport after a crash everything works great except for a bad tail wag when the main blades are installed and absolutely solid when I remove them. What gives? does anyone have a good solution to this. I tried to balance the blades as best I could. Thanks

[matthewcornell]

Sometimes a slightly bent head block can cause a tail wag. Also, did you replace the main shaft? It might be bent a tiny bit - try rolling it on a sheet of glass or some such.

Originally Posted by vfavela

I just finished rebuilding my trex 450 sport after a crash everything works great except for a bad tail wag when the main blades are installed and absolutely solid when I remove them. What gives? does anyone have a good solution to this. I tried to balance the blades as best I could. Thanks

[CoolBear]

I tried to figure out if my main shaft on my 450L was bent, rolled it everywhere, even on glass, looked great, still lots of vibration in the heli.

I finally confirmed it by removing the head and swash, then running the engine slowly:



-
CoolBear

[newbheliusr]

Sometimes putting it in a drill will do the same thing.