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Old February 6th, 2005, 06:27 AM   #1
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Spinning GG RPM on My XL1s Adapter

I have recently built an adapter for my xl1s using a still GG, with nikon lenses, a macro adapter and some custom alu/stainlesssteel rails.

Pics: www.pixelloft.com/xl1s.htm

Having done this, I am happy with the results when using good controlled lighting, however I feel a Spinning GG would be far better.

Can anyone sugguest how many RPM's the GG should be doing?? as It appears I can gear it from 16 to about 500. Any advice would be much appreciated.

I was planning on using this geared motor: http://www.rapidelectronics.co.uk/rk...p?PAGEID=80010

and this GG (I have used this allready and it is excellent):

http://www.knightoptical.co.uk/acata...iameter212.htm

in a 100mm diameter piece, drilled in the center, with an aluminium/brass axal.

Thanks in advance!
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Old February 6th, 2005, 12:13 PM   #2
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Nicholas,

What frame size do you have now without getting vigneting?
How close is it close to 24/36mm?

As for RPM, tests will tell you better than anyone else. I found that as long as you can get a reasonable amount of motion (usually for 1/60s) the blending of the grain will look good. That means low rpm (30?) You also will benefit from lower noise levels and power requirements.

The unit looks very good. I hope to see some clips or pics? of the image it produces.

Good luck.
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Old February 6th, 2005, 02:05 PM   #3
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Thanks for your reply Dan,

I am getting 36mm without vigneting I think. I was using a 36mm focussing screen before, and that wasn't vigneting.
Would you recomend a belt drive or some gears for driving the axal.
Thanks for the advice on speed, that is very helpful. I do often tend to shoot some stuff at faster shutter speeds, especially action. Would you therefore reccomend an adjustable RPM, which can be increased with the shutter speed of the camera.

Thanks again
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Old February 6th, 2005, 02:45 PM   #4
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You are welcome Nicholas,

Adjustable RPM is a "must have" for this kind of contraptions (IMHO). Use an adjustable volt regulator and a pot.

The easiest way to achieve it is the motor's shaft on a rubber ring (mounted on the GG)
http://pictures.care2.com/view/2/787532907

Obviously, the sizes and application are different, but to get an idea...

Reduction speed ratio is GG dia/motor's shaft dia. As silent, inexpensive and maintenance free as you could get. Some motors have windings for speed, some for torque. You choose for your particular case. It may require (depending on how precise is your central shaft mounted on the GG) another bearing (or two????) (with rubber ring at the opposite dia from the motor) to help stabilize the planarity of the rotating GG.

A gear box might be noisier (depends on too many factors) regardless how much grease you put in, unless you use a worm drive on the motor shaft as here:

http://pictures.care2.com/view/2/849910055

This one: http://pictures.care2.com/view/2/311786781

was dead quiet, yet fast and accurate. No need for such in your application.

A belt will work as well (as in any old cassette player, etc). A mix and match shafts and wheels game.

For more "ideas" browse here:
http://pictures.care2.com/view/1/682555803/48

I would still be curious to see a still image of 24/36 without vigneting OR GRAIN @5.6 - 8?

Good luck.
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Old February 6th, 2005, 03:31 PM   #5
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Thanks once again.
I think i will try a direct motor shaft driven GG, with a hole in the GG, nylon shim and steel shaft, going right through to a bearing on the far side. I will also find a voltage regulator, i think instead of using a gearbox as you have helpfully sugguested.

I appreciate all of your help and will keep you informed on the progress. I shoot almost everything in anamorphic, so I don't usually get 24 height, It may well vignette at 24/36.

Many thanks, Nick
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Old February 6th, 2005, 03:55 PM   #6
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you are welcome
I hope you will get a good picture.
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Old February 9th, 2005, 06:48 AM   #7
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Just a short note on flexible hubs. - The gyro effect of the gg could be an issue if you up the RPM to cope with higher shutter speeds. If you pan or tilt, your gg may momentarily move off the focal plane.
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Old February 9th, 2005, 07:38 AM   #8
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Thanks for your advice.

I have had a piece of 100mm dia glass drilled with a 2mm axal hole. I have a motor with a 2mm shaft. I was aiming on sandwiching this with 10mm dia brass plates with grubscrews for fasteneing and some form of adhesion on both glass facing sides. Do you feel this would be enough to eliminate the gyro effect.

Regards, Nick
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