Hello and thank you for this very informative website.
I have been using a Rondinax 35U for a couple of years now, and while turning the knob by hand is not much of a hardship I thought it would be a good project to find a means of motorizing it. Inspired by an example on this site, this is what I have come up with.
I wanted to make no modifications to the tank or knob, and in the interest of simplicity I have gone for a continuous rotation. I could have used a microprocessor or Geneva mechanism to provide intermittent movement but it seems to work well enough as is.
The film is loaded into the machine and it is intended to be started up dry and left running for the entire process time. There is a hold-down strap (optional) to permit safe one handed inversion of the entire apparatus to drain fluids but I find it more convenient to use two hands and omit the strap.
I would be happy to share the model of the winder knob interface, but people should be aware that I designed this to fit my tank’s winder, and my motor. Theirs may not be identical.
The video is HERE.