Rage Against the Drivetrain

Hi all. After a few frustrating nights working on installing the new motors, I tore it all down and tried something new. I’d love your feedback on it. Please leave comments here or in the YouTube comments section. Here is preferred so we can add links/pics, etc.

As always, thanks for your input!


simplicity is a long term solution.
the more complex it is i believe the less people will get involved.
If anyone want to make it complicated they have all the info available.
Cleaning roller or wet gate is a must.
Sound is also very important.
So please go ahead and finalise the project so we can start building our scanners.
The idea it to have a simple low cost scanner available to everyone.
Just finish it as the ideas and opinions will never end


Yay, simplification! I have to be honest, though I am a programmer I haven’t dove into the Raspberry Pi/Arduino worlds yet, so I am unencumbered by technology. As a mechanical engineer, I may be one of the unwashed that you speak about that could find the Kinograph “unhackable.” Or at least unreachable as I would have to invest a lot of time and brainpower to learn new operating systems and programming languages to get an even barely working result.

I come to this also thinking that the very cameras that were used to capture the film that we’re desperately trying to preserve, were themselves almost completely mechanical devices. Some were devilishly complex to achieve what they did, but the basics are pretty simple. Granted, we have the luxury of cheap digital machines now that can help us in a myriad of ways, but there is always a learning curve, that for some of us that may outweigh the benefits.

So, I default back to looking for simple mechanical systems that can achieve most of what I want, that as you say, just work.

Motor with a simple speed adjustment knob makes sense.

The drag belt on the supply spindle to provide film tension is easy to see and easy to adjust. It won’t provide the same film tension from the beginning of the reel to the end (as the diameter of the film spool changes), but as they say in Anchorman, “60% of the time, it works every time,” which might just be enough. You could even put a mechanical linkage between the tension pulleys and the drag belt so that it automatically adjusts the friction as the tension changes (this has probably already been done 100 different ways in old film projectors).

I’ve got a few ideas in my head that I’ll try to put to paper. Glad you had this epiphany!


Looks good Matthew,

The belt/tension thing you’re using to hold the reel in place might wear out eventually, that’s all I can see as a potential problem at the moment.
Rage Against the machine lol!



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Can you help me understand this? I lost all my physics knowledge immediately after my high school physics class final exam and have yet to retrieve a shred of it.

Ah, sure! It’s all about lever arms. Torque = Force x Distance.

That drag on the supply reel is a torque. To overcome it, you need to apply some force at a distance.

Since your torque is constant (the drag on the spindle), only your force and distance can change. And they are “inversely proportional” meaning if your force goes up the distance must go down. And vice versa.

So, when the reel is full and the film is near the outside diameter, that’s a big distance. So your force (tension on the film being pulled) will be low.

As the film gets to the end and it’s near the center of the hub, that’s a small distance and your force (tension) will get bigger.

You can also think of it like a wrench. It doesn’t take much force to turn a bolt with a really long wrench. But if the wrench is short, then you’ve got to put a lot more oomph into it.

That translates to there being low film tension at the beginning of the film (large diameter) and higher tension at the end of the film (smaller diameter).


In a perfect world, you’d want some clever linkage that could alter the drag and keep the force (tension) constant.

In an 80% perfect world, you may just want to set the drag at one acceptable level over the whole run of the film (knowing that the tension would change over the run, but that the film could handle it and it would be acceptable).

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Ah, thank you so much for this! It makes sense now. As a projectionist in college, I had to inspect reels all the time I would use a foot pedal to engage a motor on the takeup side, and use my gloved hand to put pressure on the feed reel. To keep the tension, I would have to adjust the pressure I put on the feed side as the film shifted over time to the takeup side. Now I know why!

This is a huge help. I think it’s clear my new “solution” is a great place to be while I move forward with other parts of the design but is definitely something to revisit and improve.

My concern with not having the ability to adjust tension on the fly (automatically, in response to changes) would be on film that’s super loose or too tight. With the tension hub, theoretically you would reach a kind of equilibrium if you fed the scanner a reel that was too loose/tight. Also, as mentioned above, you can probably find some tension setting that works well enough across a whole roll, but that will need to be adjusted for different gauges and possibly for different reel sizes. What you don’t want is something that makes too tight or too loose a wind on the takeup side. (this becomes especially important if you ever work with film on cores, not reels or splits - you do not want to be handling a loose reel on a core).

We see this a bit with our ScanStation - sometimes on old home movie reels, the wind is really loose because the end of the reel wasn’t taped properly. On a rewind bench we’ll prep the reel and get the tension to a more sane level, but sometimes it’s too tight or too loose depending on how the friction knobs on the rewinds are set. By the time it goes through the scanner and is rewound on the scanner, the tension is right where you’d want it.

It’s not uncommon for us to get reels that have different tension throughout the reel, and you can see this in how the dancer arms move. Sometimes you have a compilation of reels that have different issues - shrinkage or other degradation on some while others are just fine. Or maybe whoever wound it wasn’t being consistent about speed and some parts are loose or tight.

For reference, the ScanStation uses stepper motors for feed, takeup and capstan drive, and dancer arms on both the feed and takeup sidea. The amount of tension applied to the film is preset at the factory unless you get a special option on the newer models that allows you to adjust it from software, or if you go into the chassis and tweak the tension springs manually.

At minimum, I’d run some tests on reels that have very loose, very tight, and a combination of loose and tight film pack to see how this mechanism works.

On the PTR argument – why not just make the rollers PTRs? That allows you to use the same roller regardless of gauge - all you need to do is make a generic hub out of Delrin (or 3D print them) that fits standard PTRs - if you’re manufacturing a bunch at once these would be really inexpensive - just a few dollars each to make the hubs, probably, in a bulk order. They’re pretty simple. Kinetta uses PTRs for all rollers, as does our 70mm scanner.

I’m going back to the hub at some point, so do not fear @friolator. But this will allow me to move forward while others can help me refine that design in parallel.

You make a really good point about the feed reels being of different tightness. I hadn’t thought of that but it makes a lot of sense now that I think about it. Independent hubs/arms will help with that.

PTR rollers are very expensive. There is another forums member working on making his own, however, and I look forward to seeing how those turn out. He hasn’t posted anything yet but will be sharing his results soon, I hope.