RunRyder - Can servo slop cause vibration (flybarless)?

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Aerial Photography and Video > Can servo slop cause vibration (flybarless)?

Hogster
Key Veteran
Location: Surrey, UK

Hi all,

I'm still trying to track down a vibration problem on my heli and I've more or less narrowed it down to the upgrade to flybarless. So far as I can see, slop in the servos (gear backlash I think it's called?) could directly cause variation in the pitch of the main rotors ... is that something that could cause vibration in the heli's frame? Even at low rotor speeds?

I keep telling myself that it's probably a balance issue (as there seem to be resonant frequencies where the vibration is strongest), but no amount of sticking-little-bits-of-tape-on-the-blades seems to be fixing it

I will try converting back to my flybarred setup .... but I would really like to get it sorted with the flybarless setup as it looks nicer and should perform better than the flybarred version ....

Any thoughts are most appreciated,

Cheers,

David

05-11-2008 04:34 PM

HOMEPAGE

rroback
Key Veteran
Location: Irvine (UCI), Ca

it's possible. I think a huge part is damping, especially at our lowish headspeeds.

Rhett... I can't fly, luckily the HC Profi Can!

05-11-2008 11:51 PM

Hogster
Key Veteran
Location: Surrey, UK

Thanks for your reply Rhett

By damping, do you mean the hardness of the rubber O-rings?

Cheers,

David

05-12-2008 12:00 AM

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SeismicCWave
Senior Heliman
Location: Hilo, Hawaii

David, if I remember correctly you are flying a Logo 10 correct? I have had a lot of problem with my Logo 10 with some annoying vibration. Even with the flybar head. I finally tracked it down to main shaft stiffness. I always tried to save weight by using the hollow main shaft. Finally when I changed to the thick wall version all the vibration went away. I think the Logo 10 being a fairly old design has some flex in the main shaft and main frame. Between the two you get some sort of resonance.

05-12-2008 12:14 AM

Hogster
Key Veteran
Location: Surrey, UK

Hi Hansen,

Yes I am using a Logo 10 (stretched and running 580mm blades) ...

Really? That's interesting .... I'm using the standard hollow main shaft too ....

Although what bothers me about this is that *something* is unbalanced / not equal on either side of the main shaft that is causing this wobble. I would really like to get rid of that problem completely rather than try to hide it by using stiffer components ... if you see what I mean?

It could be that the main shaft is flexing but I want to find out why ...

Something must be out of balance, as whilst spooling up, the heli resonates as the rotor-speed passes certain points. The vibration is noticeable throughout the frame, and the tail boom will often bob up and down in sympathy with it .... I will try to make a video in the next few days showing the problem .....

At least vibration from the tail rotor is out of the question now

Cheers,

David

PS. I will try balancing the blades as perfectly as I can ... might even take them to University to see if they've got some precision scales I could use there ....

05-12-2008 12:20 AM

HOMEPAGE

SeismicCWave
Senior Heliman
Location: Hilo, Hawaii

David,

you just described the exact same problem I was facing for as long as I owned the Logo 10. I had crashed it once and rebuilt it numerous times and never gotten rid of the problem. Until one day I grabbed one of the thicker wall main shaft in my "stash" and tried it. Now it is smooth as silk.

I even ordered a couple of different heads from Vario to change over if necessary.

RC helicopters like full scale helis are strange animals. Anything that rotates has a natural resonance. Even everything is perfectly balanced. The addition of all resonance of all the rotating parts will create a different resonance at different RPM. Some times when you are lucky they will cancel each other out. Some times you are not so lucky and they will amplify each other.

05-12-2008 01:33 AM

FCM
Elite Veteran
Location: Back in Blighty!

This sounds like a plausable explanation. Remember you bent one of your main shafts David which you attributed to vibration. I would give the solid main shaft a go.

Paul.

05-12-2008 03:14 PM

Hogster
Key Veteran
Location: Surrey, UK

I will order one tomorrow and give it a shot

In the mean time I will try to weigh the blades as accurately as I can - something which can't harm and can only help

Cheers

David

05-12-2008 05:58 PM

HOMEPAGE

Hogster
Key Veteran
Location: Surrey, UK

Hi guys,

I was pondering earlier today about the main shaft ... after phoning the UK's Mikado stockist I've discovered that the only two available for the Logo 10 is the standard one, and a hardened one (I'm using the standard one at the moment). Would I really see much benefit from upgrading to the hardened one? I believe it's the same wall thickness as the standard one ....

Many thanks

David

05-13-2008 06:44 PM

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Hogster
Key Veteran
Location: Surrey, UK

Bump .... I would like to order a new main shaft ASAP if it's generally agreed that a hardened one would help over the current one.

Many thanks

David

05-14-2008 12:46 PM

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AceBird
Elite Veteran
Location: Utica, NY USA

Quote
Bump .... I would like to order a new main shaft ASAP if it's generally agreed that a hardened one would help over the current one.

You could try and see but I think it will not. My thinking is deflection will not change by hardening the shaft but my memory is a little rusty on this. The parameter that makes the biggest difference for deflection of a shaft is increasing the OD. The part I am not clear on is what role hardness plays on resonance. I would think it would change it but I don’t know by how much

Ace
What could be more fun?

05-14-2008 05:42 PM

SeismicCWave
Senior Heliman
Location: Hilo, Hawaii

David, go for the hardened one. It can't hurt.

05-14-2008 07:24 PM

meflyjeep
Senior Heliman
Location: On the ground and in the air ...

Yep, worth a try on the hardened shaft; it seems like you have addressed most other possibilities ... odd that it showed up so much when you went flybarless ???

meflyjeep

05-14-2008 08:20 PM

Griffo
Senior Heliman
Location: Canberra, Australia

How do you tell if you have a standard shaft or a hardened shaft (no sexual puns intended)?

How do I phrase this... Does the hardened shaft come with the Logo6003D or is it just a standard shaft?

I'm wondering if this might also have something to do with my vibe issue. Would be interested to hear how you get on David.

Edit: yep it turns out I already have a hardened shaft. They are standard with the L6003D

05-15-2008 04:11 AM

Hogster
Key Veteran
Location: Surrey, UK

Hmmm I've decided to hold off on the main shaft for the moment as I seem to have got the vibrations tracked down.

I've moved back to the flybarred setup and have got that running very smoothly now

The vibration when spooling up is much less noticeable when compared to the flybarless system ... I still don't understand why when there are fewer rotating components

Here's the latest onboard video I took with it:

http://www.vimeo.com/1020054

I would love to get the flybarless setup running this smoothly, it just seems it's much more sensitive/prone to vibration

Ah well, at least my rig is producing useable results again

I need to find myself a shorter flybar though .... the 400mm one I'm using at the moment is really intended for 3D ... I've heard of people using Raptor flybars and paddles - anyone have experience with those?

Cheers!

David

05-16-2008 12:17 AM

HOMEPAGE

AceBird
Elite Veteran
Location: Utica, NY USA

Quote
The vibration when spooling up is much less noticeable when compared to the flybarless system ... I still don't understand why when there are fewer rotating components

It very well could be control input from the gyros in the HeleCommand, just guessing.

Ace
What could be more fun?

05-16-2008 05:54 PM

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Aerial Photography and Video > Can servo slop cause vibration (flybarless)?

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