I had trialled something similar in a static model before hand but I wasn't sure how the measurements would pan out but essentially, yes, it is going to be that sort of mechanism.

Wikipedia (reference) describe the mechanism as a crank rocker mechanism, which handily show where I've been going wrong with my linkage length between the motor and the axe arm. I need to get a higher geared motor though, the 12v Como 50:1 motor is neither powerful enough and is too quick for this application.