Shaky video, anyone know why

[Ruud Westerhout]

Hi all,

I have had some time last weekend to finally try my TRex 450SE with the Askman APLG and a small old Minolta X31. The Minolta was taking video and it looks VERY shaky :
http://www.youtube.com/watch?v=JDT_Q0dCsMI

As I had my son taping the Heli at the same flight, You can see that the heli was quite smoothly flying :
http://www.youtube.com/watch?v=JfS7V1jdi5A

Surely this is nothing pro, but on the other hand this shake is surely not what I expected to get. I would like some advise from persons using the Askman APLG mount, what to do. I have the one with the shock-absorbers :
http://www.rstl-w.spb.ru/Helipictures/PA191953.JPG

Thanks in advance,

Ruud

[j_kookboy]

Looks like you have a vibration somewhere.

Maybe tried a few things. Put a rubber/shock plate or thin foam between the bottom of the camera and the camera mount.

Try another camera. It's possible that the minolta doesn't like that freq vibrations that running through the mount.

[Ruud Westerhout]

Thanks for that reaction :
-a plate underneath the camera ? I have the feeling this is the complete mount which is hanging on a gymbal, which is shaking. I cannot really understand what that would bring, only if the total construction will not vibrate because of the change in weight
-another camera, yeah, that's the trick. But I cannot make up my mind which one I want

cheers
Ruud

[j_kookboy]

http://img125.imageshack.us/img125/7229/88738298kp7.jpg

[Ruud Westerhout]

Wow, thanks for taking the effort and draw down that graphic.
Actually it is what I understood from your first reply. But I cannot understand the reasoning why it would take away the shaking, that's what I ment to say. The shaking is quite heavy, for my point of view and I presumed that the whole mount which is hanging under the gymbal is shaking like this together. If that is the case, the foam padding will not change that.
Please tell me why You think it will change something.

Cheers,
Ruud

[Windbreaker]

It's impossible to tell in your son's video whether there wasn't some sort of unwanted shake in the helicopter and mounting system. The shot needs to be a LOT closer and clearer to determine that. I would suggest mounting the camera on a tripod and zooming in close enough to get the mounting system to almost fill the frame of the video.

Get the helicopter to hover a few meters away and have the mounting system videotaped very close-up (with a zoom lens) to help figure out what's going on.

It only takes a fraction of a degree of yaw or a few millimeters of shifting to make this kind of shaking appear on your videos. Shooting the helicopter as a small speck in the sky won't help identify the problem.

The first step would be to eliminate as much vibration as possible.

Check for blade balance and tracking. Make sure all drive system components are straight and not bent (drive shaft, head, feathering shaft, etc.).

Also you might try shooting video with the helicopter in motion rather than hovering.

Hovering flight tends to put the helicopters main blades into its own downwash, and you can feel the increased shake. Even large helicopters tend to fly smoother if they're moving slightly as opposed to hovering over a stationary point. I've shot a lot of photos and video in full-scale helicopters and have experienced that time and again.

Make sure the Askman mount is firmly secured to the helicopter. The built-in dampeners, I'm guessing, depend upon the mount being solidly attached to the frame. If the mount is spongy the dampener's will behave differently.

The dampeners probably depend upon the camera having a certain mass to be effective. It could be the camera is lighter or heavier than the mount's design assumptions.

Also check if the camera itself is mounted securely to the Askman system.

You might also get in contact with Askman directly and get the designer's opinion. He's probably encountered the same problems and figured out the solution already.

Good luck!

By the way, that's some nice shots with the town blanketed by snow. If you have manual exposure you might want to have the camera compensate by increasing the exposure to make the white snow look whiter instead of grey -- there might be a "plus one" setting that you can use.

[crewchief]

Hi Ruud,

Wow - cold! In my opinion the shake cannot be related to vibration, per se. If you'll notice, the shake is around 150 - 200 Hz, meaning it's not related to the main drive (~2000 Hz) or tail drive (~18,000 Hz). Therefore I'd look for an oscillation caused by an underdamped condition in the camera mount. You'll also notice the oscillation is offset and your horizon is not level. Try moving the camera sideways or adding weight to one side of the mount in order to level the camera. If you're lucky this might also help to dampen your oscillation problem, as they do appear to be related. Also check to see that the spring tension in the dampeners are not pulling the mount off-center, which could also cause this problem. You can test it without flying - just hold it up by the skids with the camera installed and move it around, watching to see if the camera remains level, and how fast the system dampens out the swinging motion.

EDIT: Windbreaker's post occurred simultaneous to mine. I agree with what he says.

[Ruud Westerhout]

Hi Windbreaker,

also thanks to You for the efforts of that long reply.

I do agree with the fact that the video my son shot is not of a good quality, and probably does not help much. My main mistake is that I though the vibration was of a stronger amplitute. If the shake is actually only a few mm, then it cannot be seen in any such quality video.
I have an old Sony VCR (VX2000) which I have not been using for maybe already 3 years, but as with all my equipment I have a problem to find someone using them as I would like it to be used. My son is only 10 Years old, not having the same views as I do.

About contacting Askman, I did so just before posting this thread, waiting for his reply as well.

The quality of the video :) Well, it is a X31 3,3MP camera. It is not able to readjust its focus after the video started, it does not have audio, quite sure it does not have any such like eposure compensation. As soon as I have a better camera, I might be able to make a video which is nice. For now this cannot be expected.

I would be very glad seeing that by adjusting things I am getting closer to a smooth video. I will be checking each of your arguments (as well as the foam idea from j_kookboy) as soon as I can. I have a new ESC coming soon now (Jazz 40-8-16) and I have strong hopes to be able to use the governor then. That also might make some change.

Thanks again,
Ruud

[Ruud Westerhout]

Bruce,

nice arguments You have there. Actually if I hold the heli and move it around, the mount does not stay smoothly level at all, it more like shocks in its next position. Do I need to make the shockabsorbers lighter or stronger for taking this effect away ? I was trying some, but did not get a smooth effect.

You noticed correctly that it is not level to the horizon all the time, I think that's for the same reason. I will try to play with the position of the camera inside the mount a little more.

cheers,
Ruud

[Cryofix]

Here is one thing, if its a 3 shock system, try and tie back the springs on the shocks with a zip tie this way you are only dampening the system with the oil and not the spring, this will also allow you test that shocks are running smooth, sometimes a shock will bind or stick and cause this effect.

Make sure the shock ends are free and move clean, this can casue sticking also.

one last thing to try is find some foam, remove the shocks, and put the foam up into the swivel part of the mount, this way the foam is used as the dampner

good luck

[Tonystott]

Foam will not work as well as the shocks. Try experimenting as suggested without the springs working, and then try different oil weights. IT will take some effort to get it right. Good luck!

[Windbreaker]

Ruud...

TonyStott and Cryofix are on the right track.

The stabilization system most likely has to be tuned to a specific weight in order to work well. Support springs, as well as shock resistance, have to be matched to specific camera weight. Lighter cameras mean lighter springs and shocks with lower resistance. Heavier cameras require the opposite.

Too light and the dampeners won't have enough give to isolate the camera mount against unwanted movements. Too heavy and the mount will oscillate excessively.

In an ideal situation the camera will sit almost completely isolated from its environment, stabilized by its own inertia. That's how Steadicams work. The gimbals will allow the camera and sled to sit undisturbed in space while the suport arm moves independently.

The operator can walk and maneuver while the carefully balanced camera sled smoothly follows. Individual steps and minor body motions don't adversely affect the camera which "floats" on a spring-loaded arm and a 3-way gimbal.

Add a gyroscope to it and the inertial resistance is increased.

An intriguing engineering/design problem, isn't it?! :-)

[Ruud Westerhout]

Hi all,

all these answers look very much to be on the right track. Thanks all VERY much, highly appreciated.

I have shock absorbers on the APLG like these :
http://www.rstl-w.spb.ru/Helipictures/shocks.jpg

And as far as I know (understood) they are not filled with oil on delivery. I am not too much appreciating the fact to play with something "dirty" like oil on my table and was not even dismantling them until now. For those who did this, is this an easy process ?
My playing / adjusting was just adjusting the springs and I could not say I liked the result very much.

I noticed one screw to be loose (before I flew for filming) and I took the complete LG off to tighten it. I also had one bearing loose which I was proposed to glue back into the carbon with CA. After that was done I have tigthened all the screws and as Askman answered me I might have made them too tight (the ones with rubber).

You think you have one problem sorted, the next one comes around the corner :)

Thanks all,
Ruud

[cbdane]

If you'll notice, the shake is around 150 - 200 Hz, meaning it's not related to the main drive (~2000 Hz) or tail drive (~18,000 Hz).

I'm confused. How can you tell it is 150-200Hz from a 30Hz frame rate video?

[Razor_Racer]

I actually have the truck that those shocks are designed for. Filling them with oil is a fairly easy task, but it will be just a little dirty, so work on a paper towel.

All you have to do is unscrew the top cap, and fill it with oil (Try 30wt first). Then slowly move the pison up and down, which gets rid of air bubbles (this is where stuff will leak a little.). Then re-fill the shock back up, and screw the cap back on. And you're done!

[Ruud Westerhout]

OK, unscrewed one. It has a kind of a plastic cap under which there is clearly something dirty (oil :) ) so they did not come empty anyway. But I really cannot say they move smoothly, I mean even without the sprin. Also the smoothlyness is not even between them I would judge.
I do not have oil "in stock" here :) so I placed all back, but I really cannot get it to move smoothly, even without the heli (but with thecamera).
I only have this X31 to test, which is 165gr. When I ordered, Askman told he'd prepare it for a Canon A620, which is to be 285gr. that IS a difference.

Still I feel I am missing something, to be the reason for the gymbal not to move smoothly.

And that's before all other mentioned ideas are being checking,

Cheers,
Ruud

[crewchief]

I'm confused. How can you tell it is 150-200Hz from a 30Hz frame rate video?
Just a guess, which appears to be panning out based on the ensuing posts. I've experienced the same type problem.