Weird vibration on 6S 450L Dominator

[fergo84]

Hi guys... Can someone help me out?

Had about 10 flights on the 450L. Complete stock n never crash. At steady hover, vibration is pronounced. Can see the skids shaking violently. I'm running approx 60% on DX9 throttle curve at midstick n pitch is ard 3-4deg at mid stick for normal mode. Parameters on the gpro is close to stock. This happens even in IU1 (75% flat)

However, if I flew it around, doing some flips n piros, flew her back close n into a hover, the vibration is not there. Keep her hovering another 3-5secs, the vibration starts. Also tried moving cyclic ard(stirring the stick) during hover, the vibe goes away momentarily n come back again.
Seems like u gotta put her in steady hover for some time before the vibe starts.
On lift off, it does not vibrate until I get to about 4-5ft above the ground. Hover it 6-8 ft off the ground does the same thing

Anyone experienced this before?

[CrashNburn420]

Your head speed might be too low, 60% is pretty low and can be hard for the esc as well. DFC heads work better with higher head speeds.

[RC/DC_5000]

I've definitely had the mystery vibrations many times and its frustrating. Even though you never crashed- does not mean a part is not the problem. You can distort the TT gears from really hard flying or from too deep a V curve.

I can tell you this from very recent firsthand experience. If you don't find the source of your skid shaking- you'll eventually regret it. I was annoyed by not being able to find what was wrong with my skids shaking- I never crashed so I just kept flying. Well one of my TT gears wasn't true- and that slight skid shake was from the TT jumping around.

Lo and behold- the TT snapped in half from the stress. I lost tail control and crashed.

The 450L does not shake unless something is wrong. The vibration is still there at higher RPM. You just don't notice it as much because it tightens up. That high frequency vibration is murder on the torque tube.

[fergo84]

Sorry to hear abt the crash.

Thanks for ur inputs. I did hold her in my hand n spoil her up. I dun feel any vibration at all. It was silky smooth.

I'm starting to wonder if it's parameter related. Probably certain gains are set too high

[CBR240]

Yes, could be gain on the collective too high. Try dropping gain on collective a bit and see. I have had what I call "head shake" on my 250 after changing to digital servos, that was quite similar to what you describe. Dropping gain on the main rotor solved it.

[fergo84]

Originally Posted by CBR240

Yes, could be gain on the collective too high. Try dropping gain on collective a bit and see. I have had what I call "head shake" on my 250 after changing to digital servos, that was quite similar to what you describe. Dropping gain on the main rotor solved it.

Thanks... ill definitely try that if the other solutions suggested does not work.

Gotta take one step at a time. painful process...

[SpringerKing]

I just noticed a similar phenomena on my 450L, very few flights and never a vibe. I took off today doing some hover work and when the motor gets to full speed there's a skid vibe.

Initial inspection it looks like my front tail gears are not true or my Torque tube bearing may have shifted.

[RC/DC_5000]

Definitely agree with the possibility of the cyclic gain being turned up too high. I was flying my 600 today and noticed the skids shaking upon lift off.

I backed off the cyclic/swash gain 3 clicks and it went away :-)

That is kinda scary though because now that I think about it... the mechanical skid shake and gain skid shake were identical. Damn this hobby sometimes lol.

[Mike656]

Had a similar vibe on my 450L. Looked everywhere for the problem. Eventually found the main blades cog was about 1/2 inch out. Blades were the same weight on a balancer, just different cog. Bought new blades and haven't had a problem since

[lcc014]

Originally Posted by Mike656

Had a similar vibe on my 450L. Looked everywhere for the problem. Eventually found the main blades cog was about 1/2 inch out. Blades were the same weight on a balancer, just different cog. Bought new blades and haven't had a problem since

You could have fixed the CG issue on one of these 2 blades and then check their weight again to ensure that both have the same weight. That will save $$ to buy a new set of blades.

[MikeW9788]

Try adding a second torque tube bearing. I did on mine right off the bat and mine was always smooth. Also, don't center the bearings, always put them off center by an inch or so. If you center them you will get harmonic resonance that causes vibration. I also agree that 75 is a bit low. I flew mine at flat 85 and flat 95. At 85 in hard collective manouvers I could get wobble. None whatsoever at 95.

[SpringerKing]

Has any one ever seen the shaft that transfers the power from the main gear to the tail (has the front umbrella gear on it) get bent from tail contact on spool up?

It appears that mine is warped and needs replaced...

[alyon187]

You mean the tail hit something on spool up? If so then yes, blade strikes will cause your torque tube to become slightly bent causing vibes.

[SpringerKing]

What happened on spool up is the tail got stalled in the grass. The torque tube is straight but the front shaft with the straight and umbrella gear on it appears bent slighty.

[alyon187]

I dont think they can be bent from that, usually my gears strip out rather than bend the straight umbrella and flat gear. When I strip gears its always that flat gear.

If it looks bent then I suggest changing it... just to be on the safe side, though im just a lil ocd when it comes to how everytging runs.

[SpringerKing]

I'm gonna change it when it arrives. I think it's causing me some very high frequency vibes

[alyon187]

Have you added another bearing to the tt? If not and your still getting those high freq vibes I would look at getting another bearing for it and while you have the boom off and are changing gears, look at the trueness of the + as it rotates. Most all of those gears are off and that causes those high freq vibes as well. Ive started to use tarots umbrella gears instead because they seem to run more true than the align black ones. Just somethings ive picked up while chasing vibes.

[SpringerKing]

I have added an extra bearing, and that didn't not help noticeably. When I rotate that front assembly I can feel a higher friction area between the two umbrella gears. I am gonna replace that gear assembly and I will be sure to look at the + connection trueness.

Thanks for the input!

[alyon187]

Push those umbrella gears all the way in, I bet that's your rough spot problem. Usually you'll hear a click when they are all the way in.

[Livan75]

Originally Posted by alyon187

Push those umbrella gears all the way in, I bet that's your rough spot problem. Usually you'll hear a click when they are all the way in.

+1

They are not perfectly round so if the mesh is to tight it will vibrate... I kept pushing the mesh to tight when I fitted the boom. I had to fix the front bearing on the umbrella gear with a small dab of CA, after that no issues with the tail...