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CarbonXtreme . Midland Helicopters . HeliProz

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Aerial Photography and Video > Viabrations - how to get rid of it
 
 
jamienz
Heliman
Location: Auckland, New Zealand

My Posts This: Topic  Forum		I am running a GoPro POV camera mounted to the frame of my Trex 500 ESP. When I first duct taped it between the skids the video was fairly smooth, but once I mounted it solid the footage has got vibrations in it.

ANy tips? Thinking rubber mounts may help, but really I would like to get the heli flying smoother too.

Thanks in advance..
07-03-2009 07:50 AM
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fionn
Senior Heliman
Location: Ireland

My Posts This: Topic  Forum		Vibes

As far as I can tell, vibe elimination is one of the few areas that is not really discussed on these forums.
A number of the guys here obviously have it dialled based on the great output they are getting from their helis but nobody really divulges any of their tricks. This is understandable enough but I guess it's only a matter of time before some tried and trusted techniques emerge.

I dont do HD video (yet) but the way I go about eliminating vibes is as follows:
1. You need to get some sort of device that will give you an objective measurement of the vibes on your machine, an eagletree elogger might be sufficient.
2. Mount said vibration measuring device on the chassis of your heli before you start building.
3. Install the motor on the heli and spin it up. This is with no drive belt (or main gear) installled, just the motor.
Hold the frame with the motor running to get a "feel for it". It should be pretty vibe free. Download your G force graph and have a look, this should be your base line.
At this point you could mount your camera on the mount & hold the heli by the chassis & check that it produces smooth footage with the motor running.
4. Add the mainshaft with the main gear (or install the motor drive belt) and repeat the above, compare the graphs. If there's a significant increase in vibes you need to investigate & eliminate. Try swapping out the mainshaft and / or mainshaft bearings.
5. Add the tail tube and tail assembly, but with no tail blades.
Repeat above, check your graphs & investigate if necessary, check belt tension, blade grip bearings, tailshaft bearings.
6. Add the tail blades & repeat above process, balance blades as required.
7. Install the rotor head & repeat above process.
8. Add the flybar paddles, adjust as necessary.
9. Install the rotor blades, do a hover test.


The above is by no means an exhaustive list but I'm sure you get the idea, basically strip your heli down & rebuild it bit by bit checking for vibes each time you add something new that rotates. Should help you isolate things.
I know I once wasted a lot of time tuning things when my vibes were being caused by my motor shaft (the bell was off). Lesson learnt, start from the BEGINNING!
07-03-2009 11:00 AM
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jamienz
Heliman
Location: Auckland, New Zealand

My Posts This: Topic  Forum		wow that sounds intense! Its strange because when I fly the heli, there is no discernible wobble when it idles up or when it is hovering. Only when I look at the footage (understand this is probably the only way to see the minor viabrations).

Do you use any sort of Vibration absorbing mechanism on the camera mount at all?

Cheers
07-03-2009 12:06 PM
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fionn
Senior Heliman
Location: Ireland

My Posts This: Topic  Forum		Hi Jamie,
I got some lord mount isolators from PhotoShipOne when I bought a mast mount from them some time ago, I might try and incorporate them in the front mount I'll be putting together shortly.
The process isn't that intense, it's just that almost every normally set up heli will have at least some minor vibes as yours does. The only way to isolate the cause (that I'm aware of) is to start from the basic building blocks & keep analysing until you spot when exactly the vibe is introduced. You can then do something about it.
JeffScholl, tabb, trackhead, swch900, Derek Bledsoe & a few others are the ones who have shown smooth HD footage here on RR so perhaps do some searching on their posts.
07-03-2009 01:11 PM
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SeismicCWave
Veteran
Location: Hilo, Hawaii

My Posts This: Topic  Forum		Vibration and how to get rid of it. First of all convince yourself that it is very simple.

Now, there are really only three kinds of vibrations in a model helicopter. If you are flying electric, then there is really only two.

You have a 10,000 to 12,000 cycles per minute vibration from a glow fuel or gas engine. The next one will be a 5,000 cycles per minute vibrations from the tail rotor and the last is the 1,000 to 1,500 cycles per minute vibration from you main rotor.

Most vibration on your heli comes from your main rotor. The most popular vibration comes from your flybar.

So the first thing to check will be your flybar. Just because the flybar and the paddles are exactly the same distance apart doesn't mean that your flybar is balanced.

If your flybar is not the problem then you need to check the parts in your rotor head.

If you have changed all the shafts and made sure everything is straight then you have a more complicated problem.

One main problem is resonance from all the moving parts. Parts that vibration in different frequency that amplify each other.

So to chase vibration is to get down to basic and start at step one.

Take apart everything and rebuild them one at a time and spool up you motor to see when you see the vibration you mentioned kicking in.
07-05-2009 04:46 AM
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cranester
Key Veteran
Location: Bogota, Colombia

My Posts This: Topic  Forum		I have found after 5 years of chasing vibes that it IS important to have a well tuned heli..... but, finding the right way of isolating those normal vibes in an rc heli is whats really important. I usually need to disasemble my heli when shooting in another city, this means I do not have time to tune the heli again to be absolutely vibe free. Finding the right material for vibration isolation is the key.

Juan Crane
07-05-2009 05:01 AM
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obin
Senior Heliman
Location: wilmington nc

My Posts This: Topic  Forum		and what did you find that does this job well?
07-27-2009 05:33 AM
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SeismicCWave
Veteran
Location: Hilo, Hawaii

My Posts This: Topic  Forum		You want your isolation material as soft as possible without inducing oscillation.
07-27-2009 06:12 AM
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jamienz
Heliman
Location: Auckland, New Zealand

My Posts This: Topic  Forum		I took your advice and went through the whole heli and checked everything. My flybar was the only thing really out, and my main blades had a slightly different center of gravity each (Align carbons), so I balanced them.

Then I replaced the carbon tail blades with some KBDD ones. I test flew the heli yesterday and could not see any vibes at all, but have yet to try it with the camera on board again...

Will post some test footage soon - before and after!
07-27-2009 06:28 AM
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SeismicCWave
Veteran
Location: Hilo, Hawaii

My Posts This: Topic  Forum		I am glad you are doing something to smooth out your helicopter first.

Balancing main blades is like an art. To get a fine balance you really need a gram scale that read in .01 grams. They are not expensive and really good tool to have for building helicopters.

You first find out where the cg's are on each blade and match them. Then you weigh each blade and see which one is light. Then you put tape on the light blade to move the cg to match the heavy blade. If the light blade cg is so far off that you need a lot of tape to get the cg correct. Then you may want to put some tape on the heavy blade to move that cg also. I am assuming you know which end to put the tape to move the cg.

After the blades are matched with perfect cg's and weight then you go and attack the fly bar. First weigh the paddles and make sure they are the same weight. Then screw them in equal distance and make sure that the fly bar is balanced with the blades on the bar.

Now if you helicopter is flying smoothly with no visible vibration then go and build a soft mount for the camera. Use the softest materials as isolation without the camera falling off or inducing oscillation when the helicopter is flying.

Use your imagination in creating the mount. You can use any sort of materials as long as you are matching the weight of your payload and the oscillation. If you are mounting a light weight point and shoot camera you may need something as soft as rubber bands or soft foam. If you camera is a 2 to 5 pounds DSLR or video camera you may use some sort of rubber isolator or even wire rope isolator or steel springs.

To stop oscillation most people use the little oil filled shock absorbers from RC cars and trucks. Use them with or without the coil over springs depending on your camera mount design.

For my very first video camera mount long time ago I simply sandwiched a 1" piece of foam between two plate (carbon fiber or fiberglass laminations). You do need to put in some limiters just in case the foam rip in the air. You don't want a camera falling down as a bomb.
07-27-2009 08:19 AM
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Aerial Photography and Video > Viabrations - how to get rid of it
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