Build Phase 1, section a - Motor Assembly


#41

A-Wind and B-Wind - This is the emulsion position of the film. There are two possibilities, just as there are two sides to a piece of film. Camera original is B-Wind. A print struck from it will be A-Wind. This is because film is printed emulsion against emulsion.
From, Glossary of film terms, https://sites.google.com/site/joelschlemowitz/home

Sorry that the drawing is off 90 degrees. Replace wrap with wind.


#42

Right now I have no plans to include a platter - but welcome any designs that include that modification!

M


#43

Hi all,

Sorry for the delay in updates. I have come very very close to making a final decision on take-up and supply motors. I am just waiting for one more shipment. More details below.

WORKING NOW
Right now I have a stepper motor system working with enough torque to power the entire system:
Motors
Power Supply: 48V @ 6.3A (enough for two motors)
Controller
Logic: Arduino Uno

I have not incorporated any feedback loops into the system for speed control yet. My only focus thus far was to find a motor with enough torque and to test it with a full reel on the take up side and then again with a full reel on the supply side. I’m adjusting speed manually with a potentiometer attached to the Arduino, which in turn changes the speed of the stepper.

I will post a video of the system working this week.

ON THE WAY
I found out that pancake servo motors might be exactly what we’re looking for. They have a slim profile, do not require a driver (PWM signal for speed control), and are built for continuous, consistent linear motion. They are used for tape recorders and the like - so they’re perfect, especially if we ever decide to incorporate our own sound reader.

I found one supplier in the UK (see PDF attached), and one in China. For the take-up/supply reels, we want something like a GPN12, and for the capstan we’d be able to get away with a GPN9.

GPN12 UK cost = $420/ea. So there’s your bad news.

Right now, the stepper motor setup is around $145 each. But I want to do a comparison with both systems so we have an informed choice before we move to the next phase. Once I have the pancake servos installed, I’ll send a video of both running and ask for your feedback.

GPN12 SCS.pdf (188.7 KB)


#44

Matthew,
I purchased an old bell and Howell super8 projector from Ebay and was able to harvest enough parts to get a good start on a Telecine machine.
I plan to drive one of the sprockets from the BH proj. with a stepper and arduino uno. The stepper mtr is a 200step, NEMA 17 and per my calculations I will run it in microstep mode, 29 steps to advance one frame, pause, trigger the camera then repeat. the camera is a 5mp imaging camera with electronic rolling shutter and I am using a 12mm s mount, M12 lens. Unfortunately, there is no trigger on the camera.
If this works, then the resulting frame shots should be exactly super8 mm size with no sprocket holes to deal with.
I plan to use Debut software from NCH which will trigger the shutter.
I will be counting on the repeatability of the stepper to move the film one frame and not get out of sync with the window in the frame. Do you have any experience with steppers? Am I expecting too much?
Thanks
Johnc


#45

@tuneturkey
Sounds like pretty solid plan - but one suggestions. Instead of relying on stepper motor microsteps, you might consider a trigger in your system that tells the camera when to take a picture. The reason for this is the following scenario:

at frame 1: the microsteps are imperceptibly off by just a tiny tiny fraction of a mm.
by frame 1000: the tiny fractions have added up and your frame has drifted out of view of the camera

Instead, it is best to use something like a hall effect sensor. By adding a little magnet to the shutter of the projector, it will trigger the camera at precisely the correct moment every time.

Can anyone help out @tuneturkey with a good link to a how-to?

Matthew


#46

Good news! I found the pancake motors for much cheaper in China. I got all three motors for $250 with shipping. Very excited to get my hands on them. Will update when I have them.

Source = http://pml.com.cn/ver2en/index.html


#47

Hi, Sorry if you have already mentioned this information. But I could not find any.
Where did you purchase these PTR rollers.
Thanks.


#48

I bought a case back in 2013 from this company: http://cinemasupplies.co.uk

Not sure if that’s the best source these days. Anyone have a better source for PTR rollers?


#49

Somebody is selling PTR rollers on ebay atm:

regular: http://www.ebay.com/itm/HFC-35mm-PTR-Roller-Matte-Hollywood-Film-Co-Used-/281910282562
small: http://www.ebay.com/itm/HFC-35mm-1-1-2-PTR-Roller-Matte-Hollywood-Film-Co-Used-/272162602375
PTR cleaning tape: http://www.ebay.com/itm/3-PTR-roller-Cleaning-Tape-roll-New-/272162602466


#50

The main element that you really need is a feedback system that tells the feed and takeup motors how far to advance. It could be as simple as a limit switch, and as complicated as a encoder that relays precise position data on a dancer arm. Any system based on calculation or even a look up table is going to be a never ending challenge to make it work and keep it working. Outer diameter of the reel or core the film lives on can vary from 2 inch to 5 inch, and is most commonly 3 or 4 inches. your system must take this into consideration-- you could have any variation that is different on the feed and takeup sides.

Each of the feed and take up motors would benefit from encoders to make the speed control more precise. Your capstan motor should also have an encoder, whether you use a stepper or servo, the precision of your control will be important. Have you given any consideration to re-wind? If you need to stop within a roll, you will need to back the film up to an earlier position.

Good Luck.


#51

Here’s a supplier of new PTR rollers, as used by various scanner manufacturers:

http://www.flashscan8.us/fxsys-particle-transfer-rollers-for-scanners-processors-and-bench-based-cleaning/


#52

Hi all. I’m testing motors again and have a problem I need help with. What method is best for braking the motor? I’m using these motors and this driver. While the driver has a “brake” mode, the shaft continues to spin when in brake mode because of the momentum of the reel. I did some searching on brake methods but didn’t understand fully what the right approach is.

Options:
a.) apply brake mode and add physical mechanism to stop the reel from spinning
b.) switch direction of motor electronically and apply a signal to rotate backwards for a short amount of time. this can sometimes cause problems with back current, however.
c.) electronic braking stuff I didn’t understand on the internets…

Any help would be greatly appreciated! @VitalSparks? Anyone?


#53

[UDPATE]
From a friend came a recommendation to try shorting the motor with a relay. I found a simple diagram on this page and think I’m going to try that.


#54

Hi Matthew,
Sorry I’ve been away so long, but other commitments have kept me super busy these last couple of years.

Glad to see you have decided to pursue the DC motor route for film transport. There is little doubt in my mind that the flexible way in which they can be used is ideal for the Kinograph. The motor you linked to has sparked my interest, especially since it can be easily reversed and appears to operate over a wide voltage range. Is it expensive?

Earlier this year I started work on researching the characteristics of DC motors under different driving conditions (constant voltage, constant current, constant power), particularly with regard to film transport. For example, it seems that using constant power to create back tension in the feed spool means that film tension will remain constant throughout the full range of reel diameters, providing the film speed is constant. I still have work to do here, and am also pursuing my scheme to use a phase-locked-loop to set and stabilise the film speed, especially to compensate for damaged sprockets. Experiments with a reflective laser sprocket hole sensor have also been very encouraging. This is particularly effective with 9.5mm film as it only responds to the holes and not image transparency.

With regard to braking yes, a relay would be effective, but very high currents could damage the motor brushes. So I suggest using a series resistor - say between 1 - 4 ohms.

I’m still not finding a lot of time to spend on my system, but when I get something meaningful to report I will post back here.

Regards, Jeff