Got bad vibrations ...

[est1976]

Rebuilt after the last crash and this is the first time I have had vibes ... so bad that the horizontal tail fin goes blurry even when hovering.

Now when I remove the tail blades the vibes disapear! Does that mean the tail blades are causing the vibe or the fact that with them removed its masking it? These are the original blades from before the last crash so I think they are ok. Only other thing I have played with on the tail (other than new tail shaft) is I have 2 odd bearings for the blade grips one is 3mm thick which is standard and one is 2.5mm with a 0.5mm washer, there is no slop in the blade grips at all.

[Boggy]

if your talking about the tail blade grips Ben i would say its probably a balance problem. if the stab fin is a blur its obviously high frequency, which would point to the tail as the culprit
the tail blades dont crash well either, they are very soft and wear down and go out of balance very quickly

[Holst]

If the bearings are different weights then I can see this causing problems.
It wont take a big difference to make a bad vibration,

Is there any way to make the tail spin freely so that you can check the ballance?

[squeaky pete]

bet your tail shaft is kinked!!!! whip off the tail assemebly and turn the mains to see mate

[est1976]

Cheers Ron, yes its the tail blade grips, however its fine with just the grips spinning (even with the odd bearings) its when I add the tail blades when I get the vibes. I got one spare tail blade here ... I'll try swapping them about and if that doesnt work I'll get a new set of bearings and a pair of blades.

[est1976]

bet your tail shaft is kinked!!!! whip off the tail assemebly and turn the mains to see mate

already checked that one, changed the boom, changed the main shaft too.

[est1976]

If the bearings are different weights then I can see this causing problems.
It wont take a big difference to make a bad vibration,

Is there any way to make the tail spin freely so that you can check the balance?

You'd think it would still vibrate without the tail blades though?

I've got another 2.5mm bearing I'll try that.

[Holst]

You'd think it would still vibrate without the tail blades though?

I've got another 2.5mm bearing I'll try that.

It might be less obvious without the blades on there.

I would swap the 3mm over with the 2.5mm, it might make no difference but at least it will be the same each side.

Swapping the tail blades over sounds like the best option as one could be bent and its hard to see it.

[est1976]

tried the other bearing so I got matching bearings now still the same. tried swapping the one spare tail blade I had with both of the current used ones still the same.

One thing I noticed on this rebuild is when I look at the tail belt through the peep hole in the main frame it always used to be dead centre as far as I remember, there was an equal gap above and below the belt when viewing through the hole now the belt seems to be lower down its flush with the botton of the hole with about a 2mm gap above it (as opposed to 1mm top and bottom). If I had to guess I would say bent boom so I took it off and rolled it on glass and it seemed ok, there possibley was a 1/2mm bend over the entire length or that could have just been the large mirror just bending slightly. I replaced the boom with another and the belt position in the peep hole is the same, low down and not center. Unfortunetly I didnt check it was straight before I put it on.

So will a very very slight 1/2mm bend cause these vibes?

And should the belt always appear to be dead center in the peep hole?

[Boggy]

no ben they run low! you should be able to see a gap above the belt but not below it

[unwind-protect]

You'd think it would still vibrate without the tail blades though?

The bearing weight will probably make little difference (being close to the centre of rotation). However, a /tiny/ difference in it's thickness (i.e 2.5+0.5 possibly not quite equal to 3.0) will be sufficient to change the center of mass of the system and cause vibration when the blades are added. The same happens when the shaft bends. If the tail system is at all marginal then a tiny imbalance in the blades (such as dirt) can create a lot of vibration.

I had a batch of slightly mismachined tail hubs for my 3dx450 and it drove me to distraction trying to figure out what was wrong.

Good luck!

[est1976]

Well they both have the same bearings now so should match. But I'm still getting vibes. I wish revolution models was open. I'm going to order the right bearings and a new set of blades. See how I get on then.

[est1976]

no ben they run low! you should be able to see a gap above the belt but not below it

My memory must be failing. Thanks for confirming that!

[est1976]

well i got my order from fastlads today, i ordered some extra spares including a pack or 2 tail boom, a pack of 2 main shaft and a pack of 2 flybar and both the flybars and the booms are bent in the post ... they put it in a bloody jiffy bag didnt they. I just got off the phone to them and they are going to send some replacements tomorrow.

now i fitted the correct bearings and new tail blades and Im still getting vibes

double bummer.

[Boggy]

ben how bad is this vibration?? the horizontal stab fin will vibrate anyway. mine tends to vibrate on the left side about 5 mm till it blur's. it always has