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Thank you!
I was lead onto the idea of using a torque motor as a take up for 70mm Reels. How would this work and where can I get an appropriate torque motor for what I need? Thank You.
Why? Isn't it a JJ? If you are using O-Thane then get V belts and throw that stuff away. If you have to have a motor look towards Baldor, Bodine or equivelent. They offer adjustable torque motors. Expensive though.
Torque motors can be tricky. There are several modes that one has to allow for.
When the projector starts, there needs to be extra torque to get the reel turning.
Once it gets to speed, is has to lower the torque to that which is required to pull the film without slack.
As the reel fills up, it needs to be able to add torque to overcome the significantly increasing mass.
Only with the above do you really get the benefits of a torque motor. Some, like Kinoton, made friction boards that covered the various modes while others have used "dancer-arms" to give the motor drive feedback so it knows how hard to pull. The dancer arm also provides a bit of a shock absorber for the film so a sudden change in torque (like when it starts up), first goes into moving the arm rather than stressing the film. The longer the arm, the more time it has to react to a change.
The other way is to get really little more benefit than a conventional clutch system is to set the torque for being able to turn the full reel and then prior to turning on the projector, turn on the take up so it is at tension and hope it can react in time with out snapping the system on start up (it depends on how fast the projector comes up to speed and how much torque the motor has to overcome the mass of the reel at start up.
In short, you aren't going to just buy a torque motor and connect it up out of the box.
Torque motor with 70 mm reels? How much film does a 70 mm reel take? That is way more, than 50 lbs. The reels on some machines can take up to 2 full transit spools. And that's 150 lbs easily.
You want the motor to quickly revolve the spool to avoid slack, then have a film tension low enough to not damage the perforation, and still wind the full content with high enough torque to give a solid wind?
You want the capability to restart after a film break with 3/4 filled takeup reel, without slack?
I doubt a simple torque motor does that for you.
A simple felt friction of small diameter, like on the AAs, even that's a very bad solution. I could work for a diameter ratio of 1: 3,5 inner/ outer, if the film isn't stopped inbetween.
I have always used dancer arm controlled takeups, that made the control over PID controller circuit into a 4-quadrant motor bridge, which could accelerate and brake utilizing a DC PM motor and reduction gear.. Thereby you're able to provide enough torque to accelerate a full reel, and have a constant film tension. Easiest and safest system for film. You can use standard off the shelf motors, which is good for the price.
As other suggested system with dancer arm would fit as best, as it has feedback for tension that way. Based what Stefan told, i did also made some systems on my own. Later i did use frequency inverter and AC motor and you can acompish torq control from it, only trick way is to calculate needed torq and siže od motor and gearing for needed rpm and for torque to be regulated to be previše for film. If you want to use same friction for take up/down and rewind, that is even more challenging because rpm ratio is much wider. If you have good experiance in electronic you could take some 4q motor controller for dc motor and dancer arm feedback, or wither AC 3ph motor with inverter and also you can use dancer arm as feedback plus if driver has current control at krast, you can use it for example to limit torque. At end, also you can set torque on some level and tried without feedback, it will work, but depends how good.....
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