EARLY ITERATIONS
I originally planned to use the two sets of lawnmower gears on opposite sides of a four-bar (Fig. 1), a design that I altered after the kinematic analysis while retaining the basic idea. I also considered using a four-bar that would trace a circular pattern to spin the fan mechanism, but decided it would be much easier to use a parallelogram design to spin a shaft. Finally, I considered using a belt around the lawnmower wheels instead of a rigid bar to link the trainer and fan rotations, but couldn't find appropriate materials to attach a belt that wouldn't fall off.
TRAINER TO MECHANISM
Attaching the trainer to the mechanism was a difficult problem to solve. There is no clear way to attach a rotating shaft to the trainer fan (Fig. 2A). I experimented with using a socket from a ratchet set to fit on the bolt in fan, but that did not work particularly well. I then designed a wood apparatus that would wedge between the blades of the trainer fan (Fig. 2B).
Figure 1: The orignal fan design featured the two sets of lawnmower gears and an apparatus to attach to the bike trainer.
Figure 2: A) rotating part of trainer and B) apparatus to attach to trainer.