Just a more basic question - If the drive wheel in the toy projector engages the sprocket holes of the film, then why is it even necessary to engage them at or near the gate?
Edit - I watched again and I get it now. It’s using the tension of the film against the lever arm to move the sprocket-catching nubbin away from the film. That allows it to advance, which creates enough slack that the arm re-engages the sprocket holes. This creates tension again, but the film is stopped until enough tension builds up to pull the lever arm again.
I guess I don’t like that idea all that much since you’re effectively putting the film in tension in multiple spots. It would also seem difficult to control the tension within the gate, since the are of tension (between the engaged sprocket hole and the lever arm) all sits below the gate. This leaves the film within the gate under very little tension and would rely on squeezing the film to keep it flat, right?
Just another thought…how do the optical sensors in a computer mouse detect motion? Many gaming mice specify dpi measurements in the 1000’s. Would it be possible to use one of those to detect how far/fast the film is moving?