450 Trex 450L Wobble

[Erfan]

Hi guys!

I got a wobble issue on my trex 450L, it wobbles sideways (aileron) but this only happens on higher head speeds.
All my idle up settings are minor v shaped (no governor), the first one is between 70-75%, second one is around 80-85% and the third one is around 90-95%.

The wobble only happens on the second and third and it wobbles hard.
On the first idle up there is no issues, same goes for ordinary throttle setup (0-50-100).
The pitch is same on all idle up settings.

I'm not sure were to look anymore, I have looked at all the parts and nothing seems to be broken or bent. The blades have a small dent but I have balanced them.
I have played with both gains but it does not do anything for the wobble.

The tail holds and it does not drift but as soon as I move around it starts to wobble hard. It wobbles is even more noticeable if you fly straight and then rotate the heli 180* while still flying in the same direction (basically flying sideways).

Some info about the heli:
Trex 450L
Stock parts
3gx, latest version


Any suggestions?

 

[Tony]

You say you have played with the gains, do you mean the pots on top of the gyro? If this is NOT what you were talking about, then you need to turn them down 1 hour at a time.

If you have done that, then check for the blades being too loose, the blade grip thrust washer bolt not tight, bent shafts (main and feathering). If that doesn't work, post up some screen shots of your flight mode settings. There are 3 windows on the program. I will see if there is something amiss in there.

 

[Erfan]

Hi Tony!

Sorry for the late reply, I changed the blades just to be sure there are no balance issues. Still same problem. The shafts are not bent, have not crashed it yet
And the model is basically brand new, only half dozen flights and this issue has been there from day 1.

Yes, with gains I mean the pots on the top of the gyro. AIL around 9 and ELE around 10. Should I try to lower it even further? On my previous 450 it was little bit above 12 on both, same on my t600.
But I could try to lower it further, I thought when it comes around 10 it will not be so good, not sure were I got that from, perhaps it does not matter as long there is no drift?

The blades are not too loose and not too tight, I do the old "holding it sideways and give it a shake" trick.

I have attached pin on all my settings, also just to be clear, the gyro is installed up side down, on the bottom of the t450L. I have also made sure that the 3gx setting for installation on the bottom is active.

 

[Tony]

In the Settings Display, look at the Aileron Sensitivity and the Elevator Gain. (don't ask me why they are different names, I just don't know lol). You should adjust your pots until those read about 105, maybe as low as 95, but I wouldn't go any higher. You can do this in real time with your helicopter hooked up to the computer.

If you like the way it's flying (less the shaking), then I will keep my mouth shut on teh parameter 2 menu. But, if want it more tame, let me know and I will post up what I think you should do in that menu.

 

[Erfan]

It is kind of tame, at least I guess I'm use to how it handles but I'm always happy to try out new settings, perhaps it feels even better
Please do post and I will try it out, I have not played much with the settings there, just added more flip rate.

Adjusting those pods around 12 will give me around 105 in the menu if I'm not mistaking and I will definitly crank them up, I just lowered them to see if the shaking goes away, I guess I need to recheck the shafts again...
Do you think an extra 3gx "tape" between the unit and the frame would help? Align says in the manual that if everything is OK but there is vibration issues you can use 2 of them but I have also read that this is not so good because more tape could cause the unit to move around more and cause other issues?

 

[Tony]

To make it a little less responsive you could raise the dampening. Since you like it, you can try about 30. I usually suggest about 70 for new pilots.

With the heli on, grab the blades and try to move the blades to positive and negative pitch. Is there any slack in the links or swash? Of so that could be your issue.

And you can try another piece of tape. It's worth a shot.

 

[Erfan]

I actually noticed a bad setting, the gyro is installed upside down, that is with the label down towards the skids/ground.
But the "anti torque comp" was set to normal, that is label up towards the blades/sky. I was sure I have set it correct but I guess I was wrong and you can see it on the pics, it's set to normal and not inverted.

I have changed it, not sure if that even matters but I will try to get it up in the air tomorrow and see if it made in difference.

At home before I made that change, I removed the blades, hold the heli in my hand and started it, at higher head speeds the tails started to actual shake in my hand (I still had the tail blades on), but after I changed the setting to inverted it did not shake, it has minor vibrations but the heli was steady in my hand, keep your fingers crossed, this is hopefully it... Going to read some more about that setting and see what the issues are if it is wrong, perhaps shaking/wobbling is one of them

- - - Updated - - -

Btw, there is some slack, it seems to be in the swash, I had that swash on my old heli which had around 40 crashed
Going to try to change that as well and see if it make a difference...

 

[Tony]

Right on, keep us posted.

 

[Erfan]

Happy to say that the wobble is gone, it seems setting the correct "anti torque comp" did the trick... Although not sure why that should have mattered since its a rudder setting, but who cares, it works now

Btw, on a completely different note; Is it possible to auto rotate a 450 size heli or are the blades to small for that?

 

[Tony]

It is possible, but you have to flair at just the right time. If you flair too soon, you will stall the blades and it will drop out of the sky. If you flair too late, it will slam into the ground. It's suggested to not auto down with anything smaller than a 500 size bird. And I would go even further and say a TRUE 500 size like the Goblin 500. But practice them on the sim so you know what you are in for just in case you lose a pinion or motor and HAVE to auto it down. You will lessen the damage if you know what to expect.

Just glad it's working for you. Not sure why that mattered either, but it works. Now FLY IT AND GET IT ON VIDEO!!!

 

[murankar]

As Tony said its better with a 500 or bigger heli. On a 450 you have to come in hot and get your transition to positive pitch just right. I would practice the stick moves in the sim. I can auto a 360 in sim but in real life the heli acts a little different so I dont even attempt it. If I do auto it I am not to far off the ground, I use it to just land the heli while not powered. It makes for a smoother landing. Plus in case anything happens while landing I am not powered.

 

[Erfan]

Sorry to say that you were right from the beginning Tony, it was a bent main shaft
Not sure how since it has never been crashed :s

But the comp setting was bad as well, it did help a bit changing that but changing the main shaft seem to almost have made it perfect. Just pure luck that I even noticed since I never crashed couldn't imagine it being bent...

But I will also look at the feathering shaft and swash, the swash is old and been in many crashed, it seems to work fine but there is a small up and down play in it, the reason I wrote almost perfect is becuase it feels a bit "snake" like going high speed forward, but then it was windy as hell today so not sure if it just was the wind.

One thing I noticed also is that when going forward in high speed and nudging the nose up (ele) it feels a bit like it jumps a little up and down (the nose), hard to explain but I know from my 600 and 700 that it should not behave like that, but perhaps it was the strong wind playing with me... But it does not shake any more at all, at least I'm moving in the right direction

About the auto; I saw couple of videos 450 autos, like u said the timing of the flair seemed really important and a really small window, almost at the ground, couple of feet at most.
The 600 & 700 give much more room for that timing, couple of hours at the sim should do the trick or couple of rebuilds

 

[murankar]

Enough hard landings will bend a main shaft along with blade grip spindles. Parts get old and need replaced.

Sounds like you have a dolphin or porpoising going on. I heard that this is caused by one of two things, to high of a head gain or retreating blade stall. In order for it to be the later you would have to be flying faster than the head is spinning.

Sent from my LG-E980 using Forum Runner

 

[Tony]

Yeah I have gotten into the habit of checking the shafts after every hard landing. Glad you got her stable though. So... where's the video?

 

[Erfan]

Enough hard landings will bend a main shaft along with blade grip spindles. Parts get old and need replaced.

Sounds like you have a dolphin or porpoising going on. I heard that this is caused by one of two things, to high of a head gain or retreating blade stall. In order for it to be the later you would have to be flying faster than the head is spinning.

Sent from my LG-E980 using Forum Runner

It's doing the dolphin dance
What do you mean with "to high of a head gain"? You mean gov gain? I don't use any gov on this one, just minor v-shaped throttle around 80-85%.

Not sure I truly understand the second reason, flying faster than the head is spinning? U mean diving and having a lot of wind pushing from behind? Going up in head speed seems to only make it worse...

It does not wobble or shake, just the dolphin dance going on in fast forward flight... I think it has to be a vibration issue, somewhere...

I will try to get in on a video, if nothing at least Tony can get a good laugh from the dolphin

 

[murankar]

High head gain is the gains for aileron and elevator. Those two combined make the head gain. If you go into fast forward flight flight and the heli is not tuned correctly for fast forward flight then you may see a pitching up in the nose.

As for retreating blade stall, its a scientific thing I just heard about. Justin pucci actually explains what that is in this weeks episode of RCHN 2.0.

Has something to do with the forward speed speed of the heli and how the retreating blade looses lift. First I have heard of it. So I really can't explain it anymore then that. Listen to the beginning of April 27ths show (which should be Mondays episode).

Sent from my LG-E980 using Forum Runner