@PM490 here’s what the contractor had to say. I agree with him (although I think you could probably mount the sensor at the gate without contacting the film directly). I would put this mouse idea in the “someone should definitely try it at some point” bucket for now while we move ahead with what we have more confidence in.
This is an interesting DIY approach, and something I would be interested in pursuing for future projects. However, there are a couple potential issues with this approach.
1.) Optical mice are calibrated to be on/touching a surface. If we are to track the movement of the film, we would either need to modify an optics and mounting of the sensor in order to work on the film directly, or we would need to have a secondary encoder that the optical sensor system would be reading. These aren’t deal breakers in and of themselves, but a potential challenge.
2.) The speed of sensor may not be calibrated for the speed of the film. While you do get a good deal of accuracy, it could be that when you are running at the full film speed you get errors in distance compounded over time. I’m only guessing this based on the video, and variable readings HomoFaciens is getting when changing the motor speed.