tracking down vibration/shudder - anyone had a bent head block?

[matthewcornell]

Hi All. I am tracking down a noticeable vibration/shudder on my P500. It happens when spooling up/down, and also during some moves, including aileron tic tocs. One thing I hadn't considered is a bent head block (AKA main hub), but it would make sense. Question: Have you had yours bend after a crash? Thank you.

[dr dremel]

So far my only crash was a full positive punch out 6 feet from the ground - inverted (brain was still upright). No bent head, but spindle, shaft, flybar, blades etc

How old are your head dampers?

[matthewcornell]

New dampers tried already, but thanks for the idea. I might bite the bullet and buy a new one just to check. It's still flyable, as yet.

[matthewcornell]

Head block was not the problem. FYI still figuring it out.

[solex227]

I also have the same vibration ... i have changed the main shaft.. but I'm starting to believe in my just be the bearing s.. plan on changing them out tonight. ..

[isogloss3d]

Have you replaced the tail case/shaft bearings recently?

I had the same shudder on spool up/down. On the bench (static test) the tail case bearings seemed fine. However it turns out they were pretty well worn and one failed in flight a couple weeks later. I replaced the tail case w/bearings ($12) and the shudder is gone and the model is much smoother now.

[matthewcornell]

I'll redo the bearings, but this was one of the first things I checked. Thanks for the idea.

[crickr1]

Do you have cnc 3rd bearing mount? Had a stock mount wear and bearing became sloppy. Also reason i changed from plastic frame. Had same type of wear in plastic frame. 2 yrs since cnc mount and no problems.

[solex227]

Originally Posted by crickr1

Do you have cnc 3rd bearing mount? Had a stock mount wear and bearing became sloppy. Also reason i changed from plastic frame. Had same type of wear in plastic frame. 2 yrs since cnc mount and no problems.

Crickr I think you are on to something.....
I have cnc servo mount and 3rd bearing mount.. an the vibration appeared to show up after my last crash. I stared to pick through the head and man shaft .. but found nothing wrong or bent. Just to be sure I replaced both the main shaft and the spindle shaft. I ran up the bird on the bench (no blades) and found the same vibration on start up that would smooth out after a few seconds . So, I took the heli apart again and found the 3rd bearing on the main shaft had ever so slight been knoched... so I replaced all 3 bearings ... finishing up tonight and will tell you if this is the fix that worked for me..just might be a bad 3rd support bearing...finger crossed..

Matt did you find a solution to your vibration issue?

Solex227

[matthewcornell]

Originally Posted by crickr1

Do you have cnc 3rd bearing mount? Had a stock mount wear and bearing became sloppy. Also reason i changed from plastic frame. Had same type of wear in plastic frame. 2 yrs since cnc mount and no problems.

Do you mean one of these?: http://www.msh-direct.com/cnc-3rd-bearing-support/

An aside: What CNC upgrades would you recommend? I see ones like the tail pulley... The only thing I've done is the thrusted tail bearings - I was chewing through the radial ones like candy.

Originally Posted by solex227

So, I took the heli apart again and found the 3rd bearing on the main shaft had ever so slight been knoched... so I replaced all 3 bearings ... finishing up tonight and will tell you if this is the fix that worked for me..just might be a bad 3rd support bearing...finger crossed..

I replaced all three of my main shaft bearings early on, though I don't have the CNC replacement part at the bottom. I don't feel any play, but maybe it's subtle.

Originally Posted by solex227

Matt did you find a solution to your vibration issue?
Solex227

Nope, but thanks for asking. I thought it might be a FBL gyro issue (I'm not happy with the Skookum on it), but I'm at a loss.

[crickr1]

Yes , that is the part. I would also suggest , the cnc tail gear, and all pullies.

[matthewcornell]

Originally Posted by crickr1

Yes , that is the part. I would also suggest , the cnc tail gear, and all pullies.

Thank you. A $60 upgrade - well worth it?

[crickr1]

Originally Posted by matthewcornell

Thank you. A $60 upgrade - well worth it?

Most definitely, Those are the first and primary upgrades most will recommend on the Protos.

[solex227]

Matt

I'm going to keep my comments here ... you also mentioned that the collar slipped on the main shaft when you had your mishap in another post. Funny enough, I reported the same type of problem when I crashed a week or so ago in the (What did you do with your Protos TODAY) thread. In my case the collar failed not just slipped, the impact snapped the collar loose. needless to say my vibration problem started after that particular incident. In any case I do believe it was the third bearing for me and I found that replacing all three bearings solved the issue with the vibration for me. Last night on the bench the problem vanished... I hope you track down the issue soon and get back to flying...

Solex227

[matthewcornell]

I ordered the cnc parts and will see if they help. It's still shuddering. I'll pull the lower bearing to see if it or the holder is bad. Will update.

[matthewcornell]

While I'm waiting for the parts, I thought I'd give an update. I tried a major change by replacing the Skookum SK540 with an ikon. I figured that if the wobble/shudder went away then it was a gain thing with the sk. Guess what - shudder is still there, so it must be mechanical, right? I'm hoping it's that third bearing holder underneath...

[aterren]

For what it is worth, I have bent a head in an inverted crash. It was a very hard crash ant the head was obviously bent. It also took out the swash.


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[matthewcornell]

Originally Posted by aterren

For what it is worth, I have bent a head in an inverted crash. It was a very hard crash ant the head was obviously bent. It also took out the swash.

Thanks for reminding me about the swash. I suppose that is the next thing to check. But I saw zero slop in it when eyeballing.

[matthewcornell]

Amazingly, still debugging this. I've mostly learned to ignore it, but I wondered if your main hub holes look like. The one on the left is newer than on the right. The vertical oval is standard, correct? But I wonder if some side-to-side movement might cause the wobble. With a feathering shaft inserted without dampers, I can do a sideways see-saw - there's a little slop, in other words. Is yours like this? Thanks!

[Jumna]

You wore those out! I'm looking at one that looks perfectly round, so maybe oval could be an issue. Btw, I had to retire this one since it developed a crack in the metal below the hole in the middle that was for the flybar. Also, I've put the bolt in wrong and noticed that then the head really rocks since it isn't tight enough.