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Aerial Photography and Video > Chosing AV mounts
 
 
Twin_squirrel
Senior Heliman
Location: Wiltshire, UK

Hi all,

I'm in the process of selecting the anti-vibration mounts for my camera mount. I'm just wondering if you guys are using a trial and error system for selection or whether you use some formula.

To my mind the highest deflection and lowest frequency vibration comes from the rotor head... about 30Hz using these asumptions I have selected the 5210 mount from Barry controls, probably a bit large for the job but relatively cheap for me (I already have 4).

Comments please as I am not very bright.

Cheers

David
06-13-2003 Over year old.
HOMEPAGE  
 
 
FlightPower
Veteran
Location: Herts UK

Just from looking arround RR RV&P it seems the experience of these Barry mounts on the Bergen Observer suggests that they are generally good but they let through some of the high frequencies. This probably means you need a second line of defence as well. Check out the images on www.rcwhirlybird.com, by all accounts that system functions superbly for stills and video. There is a final set of isolators at the base of the RCWB camera mount. As a last line of defence strategy I'm currently fooling around with silicone gell isolators used for car CD players (like MPA). MPA is getting some of the best slow-shutter performance on RR.

Of course the easiest way to handle this (for stills) - though typically at a cost to video performance - is to separate the camera mount from the heli entirely using foam and bungees - see heliraptor's posts, he's putting out some of the sharpest still shots on RR (partly thanks to a great camera) using a clever but technically very simple system of enclosing skids and top-rail of his mount in a foam tube with about 20mm separation. The other cool thing about heliraptor's work is that he's using a heavy camera and lightweight plastic components elsewhere in the mount. For vibration isolation you need to "think backwards" i.e. the camera payload needs to drive the mount to a standstill at the last stage, so heliraptors solution naturally benefits from this logic.

Hope this is usefull food for thought,

Good luck!

Julian.
06-13-2003 Over year old.
 
 
Twin_squirrel
Senior Heliman
Location: Wiltshire, UK

Thanks Jullian,

Yep, that certainly is food for thought.

I do have one question though, with 2 different AV mounts is there not an increased chance of some resonance beig set up between them?

My camera is also very heavy, I am planning on using a Sony TRV140 which weighs around a kilo (2.2lbs) perhaps this will give me a head start with so much damped mass?

David
06-13-2003 Over year old.
HOMEPAGE  
 
 
FlightPower
Veteran
Location: Herts UK

Hi,

Regards resonance.

There are two concepts that we are working with here, there's the spring and there's the damper, these are not the same thing although some assemblys (your barry mounts included??) may exhibit both properties. A typical car suspension uses separate springs and shock-absorbers. So to answer your question on a theoretical level, if you have two sets of springs combined in a system with no damping effect - of you hit one of them then the system could resonate for ever at a harmonic of the combined natural frequencies of of the two springs. (actually you don't need more than one perfect spring to cause this kind of effect - the hanging bungee does wonders to disconnect vibrations but the cost is having a hanging load that wanders around forever at an un-damped low natural frequency = swing, requiring further countermeasures to bring it to rest for video work etc - (or you can just ignore it for stills shooting at a reasonably high shutter speed with attention paid to steady flight).

For the ultimate effect, the object is to try and get spring and damping properties to match so that the spring absorbs the energy of sudden or repeated impacts and then instead of "bouncing back" feeds the energy to a damper that returns the system to a steady state. In this case a destructively-interfering twin-layer would seem ideal beacause you would have a section of the mechanics that expands and compresses in oposition with a sum-zero output at the camera. Calculating these properties is complex but a practical work-round is to look out for sub-assemblies of things that have already received the $Million R&D treatment i.e. large auto CD Changers is a good bet for the kinds of weights you have in mind - especially viscous silicone enclosures with matched springs that offer spring action and damping in all directions.
I have some Pioneer and Nakamichi spring-damper assemblies that I'm currently testing with in an attempt to tune assemblies for both light and heavy cameras for a Logo 20 and X-Cell respectively. So you have a choice to join the experimenting or watch this space as and when I have a chance to progress this

Cheers,

Julian

P.S. I don't know the TRV140 (I have the TRV950) - but I have a suspicion that Sony camcorders with the Super Steadyshot feature could be mounted pretty hard to the heli mainframe with well-matched rubber isolators to prevent high frequencies damaging the components and effectively let the camera take care of the rest, but to answer your question, yes you're right, any 2.2lb lump has some decent inertia to work with.
06-13-2003 Over year old.
 
 
Twin_squirrel
Senior Heliman
Location: Wiltshire, UK

Jullian,

Some great info in that last post thanks. I think I will use the Barry mounts in the first instance and see what results I get and use that as a baseline then start experimenting with additional spring-damper assemlies to eliminate the expected high frequency vibrations at a later date. I suppose mount stiffness has a large bearing on the ability of the dampners to do their job correctly. Be sure that I will post some results as soon as I have them.

The TRV140 only has standard steadyshot built in so we shall see how that goes.

Still trying to work out how to include the barry mounts in my system....

D
06-13-2003 Over year old.
HOMEPAGE  
 
 
FlightPower
Veteran
Location: Herts UK

I think cmartin has kindly figured it out for you....

http://runryder.com/helicopter/t50590p1/

JC
06-13-2003 Over year old.
 
 
Twin_squirrel
Senior Heliman
Location: Wiltshire, UK

If only it were that easy These are the mounts I have Barry 5205/5210

D
06-13-2003 Over year old.
HOMEPAGE  
 
 
Twin_squirrel
Senior Heliman
Location: Wiltshire, UK

Should read Barry 5205/5210 HT

Sorry
06-13-2003 Over year old.
HOMEPAGE  
 
 
Twin_squirrelSenior Heliman - Location: Wiltshire, UK -
This is the tilt unit of the mount, It's not pretty, the workmanship is awful and I don't have high expectations but it is quite light, think of it as a technology demonstrator

06-13-2003 Over year old.
HOMEPAGE  
 
 
MPA
Elite Veteran
Location: Australia

Quote 
the workmanship is awful


Looks ok to me.

Im on to about MkV
Mk I, II, III and IV are all in bits in a plastric tub and Im glad I didnt go overboard on the finish as it would have been wasted.
Id suggest spend your time on the end finish when youve decided that the rig you have is the final design you will stick with and you wont know that till you go out and do the shots and get results to work from.

On the vibration dampening.
The silicone dampers Julian refers to soak up the high freq vibrations, I wouldnt not imagine they are so good on low freq vib, that said using them alone is suffice to not have any rotor vibration which is the lowest freq applicable.

I run a glow engine not a gasser and they dont have as much vibration issue as gassers but my thinking is if they are enough to dampen out the head vibration then they should habndle the higher freq engine vibration, being the liquid dampers can handle a much broader range of vibration.

As far as the silicone dampener being resonant with another dampener I suspect it would not be an issue as the silicone or liquid dampening has a much higher dampening frequ bandwidth, as well as not having any sprung properties in it to cause an undulation or resonance.
The liquid makes it a dead damper incapable of oscilating itself which is why they are such a good damper.
Just imagine a water bed full of liquid silicone, no more waves.

Note the specs on industrial liquid dampers over sold mounts
and note the price too which makes it worth hacking some old CD players to get them in the sizes we need.

I went to a Alpine car audio dealer and told them what I wanted and why and did they have any old dead CD players.
I got a pile of them to go through.
06-14-2003 Over year old.
HOMEPAGE  
 
 
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Aerial Photography and Video > Chosing AV mounts
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