Hi,

I have built my first CP helicopter it is a EXI TREX 450 Sport Clone, it was configured and flying great. I had ran about 4 batteries through it when one of the screws backed out of the feathering shaft (despite thread locker) and I lost the blades midflight. Luckily I was about 6 inches off of the ground when it happened so the heli just came down on the grass.

After I got everything rebuilt I had a problem with the helicopter spinning counter clockwise (opposite of the rotor), I fixed that by ajusting the servo location on the tail boom to add a little bit of pitch to the blades. After that was solved I started getting a wobble when I approached 1/2 throttle.

Further investigation revealed that the blade pitch is off on one blade at midstick. BUT they are dead on at low stick. It does not make any sense to me how this could be. So I ajusted the blades to match at midstick and now the heli tries to roll over as soon as it takes off.

I am affraid I am now a little over my head. Any help would be appreciated.

Have you checked the feathering shaft?

Yes, I did give the head a once over. Nothing seems bent or out of place. I made sure the screws going into the shaft were snug, but not too tight. Also the feathering shaft and main shaft are not bent.

Here is a short video of the problem. I reset the blade pitch so that both blades match at zero stick, and the heli can fly again, but I am still left with this wobbling.

TREX 450 Sport Clone Wobble Problem (0 min 21 sec)

When you originally ran it, before the blade grips came off, did it fly smoothly those 4 flights?

About your feathering shaft, are you sure you put the blade grip bearings, thrust bearings, and washers in the correct order? EXI doesn't care how they put it together originally. I recently experimented with removing a washer out of the blade grip assembly which resulted in my blade grips loosening at times. Reference the align manual and make sure you have everything in order. Also make sure the blade grips are not binding on the feathering shaft, spin them around before you connect the ball link, it should feel smooth... I'm currently having a ratcheting problem in my exi pro blade grips, which I'm hoping is bad bearings (this gave really bad vibrations in hover when I decided to test it the way it was).

Vibration/wobbling could be lots of things, but check: (since you already checked your main and feathering shafts, did you roll them on a flat surface to check?)
-possibly hovering with low headspeed - does it still happen if you increase the throttle in the throttle curve?
-flybar length equal on both sides, measured equal with no paddles first, then measured equal again to paddle on each side, both paddles @ 0 pitch
-blades not balanced or tracked properly
-main gear assembly bolt too tight - be careful with this one, and definitely use blue threadlocker, but this doesn't need to be so tight that it deforms the gear being level... exi main gears suck anyway (I have a EXI pro).
-wind can make it seem like it's flying like crap sometimes... on a calmer day problems go away.

maybe something else, I'll have to think...

Thanks for the reply, yes it flew perfectly at first, had to adjust the gain, and give a few trim clicks of cyclic but other than that it was great. I did follow the trex 450 sport manual when I re-assembled the feathering shaft. When I was originally building it, I just backed the screws out and applied threat locker, so I cant say if it was in the right order at first..

At first I thought my problem was with the feathering shaft. I thought maybe it was too tight and therefore stopping the flybar from moving freely, fixed that. My blades were slightly off balance (one had a small chip taken out when it was ejected) fixed that, and ordered a new set of blades. I do test my shaft s by rolling them. Both were fine. I think my difference in pitch was because of my trim, set trims to zero and the blades track better now.

I am going to give it another flight today, if I still get the wobble I will try to increase my throttle. I think you are right about the wind, when the wind kicks up the wobble increases in intensity.

Thanks again for your help.

Something i noticed today. I'm in the process of repairing my heli when i noticed the tail wobbling when i tried pulling the belt. I thought it was a bent tail shaft but it was still there after replacing it. Turns out one of the tail blades was bent slightly. I had to take them out so i can compare them side by side, and when i straightened it out, the wobble went away. I'll know for sure when i finally finish, but you may want to check yours too.

Thanks,

I will check the rotors.
I flew this morning and although it is less aggressive, the wobble persists.

I have double checked the flybar length and it is exactly in the middle. As well as the paddles. I did notice a small bend in the flybar almost undetectable, I have a new set of flybars arriving tomorrow so I will replace that.

The blades track perfectly
The blades are balanced
The shafts are not bent
The flybar is centered
When I spin up the head with no blades i do not detect a wobble and I have even held the helicopter and did not feel much vibration although I am not willing to perform the same test with e blades on.
Increasing throttle speed yielded same results.

New flybar and new main blades will be here tomorrow and I will switch them out and see what happens.

Thanks again for you help everyone!

Originally Posted by RFDelie

Thanks,

I will check the rotors.
I flew this morning and although it is less aggressive, the wobble persists.

I have double checked the flybar length and it is exactly in the middle. As well as the paddles. I did notice a small bend in the flybar almost undetectable, I have a new set of flybars arriving tomorrow so I will replace that.

The blades track perfectly
The blades are balanced
The shafts are not bent
The flybar is centered
When I spin up the head with no blades i do not detect a wobble and I have even held the helicopter and did not feel much vibration although I am not willing to perform the same test with e blades on.
Increasing throttle speed yielded same results.

New flybar and new main blades will be here tomorrow and I will switch them out and see what happens.

Thanks again for you help everyone!

How tight are your blades? Maybe they're not able to straighten themselves out on spool up, or maybe they're even too loose (but you say your tracking is good so maybe not loose).

Try flying with a flat throttle curve, something like 80% all the way up, this might help with the wind. Of course start the heli in norm, with a gradual/standard cuve, then when hovering or when the heli gets up to speed in normal, switch over to the flat throttle setting.

I don't know your experience level, so I'll also add be careful with idle up if you have never used it... it may make the heli jump a little when switched on depending on the difference in settings from normal to idle up. But be alert and you'll be ok and learn to adjust. You may know this all already but just in case.

"...small bend in the flybar almost undetectable..." if you can detect it, it's probably not the best flybar. A straight flybar is pretty critical to stable hover and flight.

The training gear shakes the most, and could cause vibrations to oscillate. Though probably not your main problem, and maybe dangerous for your machine but can you fly without the gear?

Also the main gear & tail gear aren't warped? Or is there a lot of slop or play by your main gears if you pull up on your head?

Also make sure the flybar is not too tight. That training gear you have on there can also induce harmonic vibration. Take the training gear off and see if it helps!

Thanks Guys.

I like to keep my blades are tight enough that they do not pitch on their own, but still allow the fly bar to swing when i quickly rock the helicopter in my hand. I had tested it a little bit more today. I think you guys are onto something with the training gears. it does seem to amplify it. But guess what? After a few take off, and landings the effing screw on the effing feathering shaft came out again, I was just spinning up, and my blades (and bearings) shot off the heli again landing 50 feet from the heli in opposite directions. When I put them on the last time I glopped the thread locker on. I cant believe they came loose again. I think I am going to have to use the red stuff. Anyway, I am set back another few days until new bearings and collars arrive.

Also my tail gear is warped, but it came that way. I upgraded the main gear, it is perfect.

This is my first 6ch CP so I am a novice, but I have been flying 4 channels for a while so I am used to the controls. Building my fist one was bitter sweet. I have had a few issues while ordering the right parts, mechanical failures, and configuration learning curve, but I have learned a lot more about them than I would have if I had ordered one RTF.

what i see is the gyro gain is to high ,you might want to turn that down at 5% until the wag goes away

I wouldn't use red threadlocker. I had the same problem with my blade grips. I had to clean the screw hole and the screw, get all the old threadlocker and possible oil out and re-apply... I apply it with a toothpick into the screw hole, none on the screw directly. I ended up using a new screw anyway, just to be sure.

You have a better heli building it usually. Most RTF 450's suck and you will spend the same amount of time setting it up properly. Exi ain't bad when you work out the bugs.

How loose is your belt? Is your belt in good shape still, no bad areas?

lugnutz, I had that thought to, it was not the gain, it does look similar though, but the gain is the first thing I checked. I have a feeling after I replace he blades (which are chipped), the tail drive gear and the fly bar it will go away.

Finguz, I will try that before going to the red locktite, thanks. My belt is in good shape, no visible damage. Using a fair amount of pressure I can move the belt about halfway to the other side behind the drive gear.

Originally Posted by RFDelie

lugnutz, I had that thought to, it was not the gain, it does look similar though, but the gain is the first thing I checked. I have a feeling after I replace he blades (which are chipped), the tail drive gear and the fly bar it will go away.

Finguz, I will try that before going to the red locktite, thanks. My belt is in good shape, no visible damage. Using a fair amount of pressure I can move the belt about halfway to the other side behind the drive gear.

I run my belts somewhat tight. BTW Align belts are WAY better, they're not a real soft rubber, you should check them out... worth the extra $5 than exi. And they run smoother/better. My exi pro is belt driven.

At least try new bolts before red loctite. However the trex450prov2 manual says to use red on everything, and to heat it before removin again... which I'm not doing, I'll be using blue as usual.