Film-Tech Forum ARCHIVE: Shaft encoders on Centuries?

This is topic Shaft encoders on Centuries? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by John Hawkinson (Member # 1135) on 05-10-2008, 05:09 AM:

"Just for fun" (i.e. on the cheap), I'd like to mount shaft encoders on a pair of Centuries. Is there a recommended mounting location and style of encoder?

Back in 2004 in this thread Steve K. recommended mounting to the front shutter shaft.

Most of the cheapie shaft encoders seem to have awfully small integral shafts (e.g. 6mm), though, so I'm a bit puzzled at what the easiest way to mount to the shutter shaft would be...a pair of pulleys and a small belt? Anyone have any photos of an installation to share?

(I suppose on-the-cheap the shuttershaft may not be the best choice, since it needs to handle 24fps * 60min/s => 1440 RPM; but a 16-tooth sprocket only needs 360 RPM. Still, newark.com is giving me stickershock, e.g. $50 each).

Thanks.

--jhawk

Posted by Pete Naples (Member # 761) on 05-10-2008, 05:40 AM:

We've done it with castellated drive couplings off the shutter shaft before now. The shaft encoder itself being mounted on a small bracket bent up out of sheet metal.

example coupling

Posted by Louis Bornwasser (Member # 3063) on 05-10-2008, 05:53 AM:

On Century R3, I have always used the soundhead main drive shaft: slower rpm and good place to mount gear.

In certain locations, certain to attract this kind of work; I have used the direct drive Century, but with the "wrong" shaft in the soundhead. Plenty of shaft sticking out since the gear to drive the head is not used.

Alternatively, just place any gear under the projector drive belt to drive your encoder and adjust the software accordingly. Louis

Posted by Mark Gulbrandsen (Member # 72) on 05-10-2008, 09:17 AM:

I ran location for years with encoders mounted on the top front of the R-3 (away from any oil drip and large moving belts and pulleys) and an 1/4" wide X-L timming belt drive(.5-1 ratio) up to the shutter shaft. I believe that Steve K. and I came up with that mounting location together one day. The whole setup cost less then 10 bucks per projector for the pulleys, belt, and mount. Of course the actual rotational encoder speed you require also depends on your encoder and the dubber electronics... 1 to 1 or .5 to 1, etc., some dubbers have switchable encoder frequency inputs! The encoder was mounted on a simple L bracket that was easily removable by two set screws. Another benefit of attaching the encoder to the shutter that also helped me a couple of times on front projection jobs was being able to use the direct coupling... encoder to projector shutter to keep the projector shutter in perfect phase with a camera shutter. Today's modern Panavision and Arri production filum cameras however can merely sample the light frequency of the projector and "remember" the phasing... then shoot film while keeping perfect shutter phase.

BTW: Higher end Honeywell and other brand shaft encoders as used on Magnatech and MTM dubbers are in the 400.00 to 1000.00 price rannge new! They use glass encoder disks and multiple opto-sensors with electronics to develop the quadrature output.

Posted by Paul Mayer (Member # 355) on 05-10-2008, 01:03 PM:

John, Boston Light & Sound has been doing this for years using a pully and belt on the shutter drive shaft. The encoder is mounted on a sheet metal plate drilled so as to mount in place of the lower hinge for the non-operating side door. Or for really quick set ups the plate can just be clamped to the picture head case with a couple of small vise grips.

Posted by Gordon McLeod (Member # 33) on 05-10-2008, 01:29 PM:

Ketchum makes a nice shaftencode in a DTS reader type bracket

Posted by John Hawkinson (Member # 1135) on 05-10-2008, 03:32 PM:

Thanks guys!

Any photos?

This is for custom software, so there's no need for me to hit any particular number of pulses-per-frame, so I'm relatively free in that regard (though I guess it might be nice to maintain dubber compatibility. How many pulses-per-frame are they typically? Or is it pulses-per-perf?)

--jhawk

Posted by John Hawkinson (Member # 1135) on 05-11-2008, 06:06 PM:

One of my colleagues pointed out that, if the projectors have SRD, you could trigger on the sprocket holes it sees in the video output. (Unfortunately the particular projectors that I'm doing this one don't have SRD...) I'm also not sure if you'd be able to detect backward motion that way, but it'd still be a neat trick. Instant-dubber-interface if you have SRD...

--jhawk