I think the middle knob you are missing is for speed tuning. The knob is turned slightly left or right which closes a switch which then causes a motor to drive the tuner. You obviously have some missing parts. "Robot" dial is a neat name but "shutter" dial better describes how things work. Turn that lever and dial panels should slide out, presenting a different band. If turning the lever does not do this, you've got even more problems. Sounds like your set might have been cannibalized at some point.
:How does this Robot feature supposed to work? How do you tune this set? It apears to have had two belts but both are gone. I can tell where one went but the other is not obvious as to where it went. There is a knob missing in the middle and no shaft to put it on. In the middle there is a lever and then a big knob and then the shaft ends but apears to need another knob on the end of the shaft but no more shaft. Don't get it.