1. Introduction 2. Design Considerations 3. Kinematics 5. Results & Discussion
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 modifed 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.
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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 unsuccessfully with using a socket from a ratchet set to fit on the bolt in fan, but that did not work particularly well. I then . Then, I designed a wood apparatus that would wedge between the blades of the trainer fan (Fig. 2B).
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Figure 5: The second and third gear reductions. The final gear, the large lawnmower wheel, serves as link two for the parallelogram four-bar.
FOUR-BAR MECHANISM
The last lawnmower gear drives a parallelogram four-bar made from PVC pipes (Fig. 5).
Figure 5: A four-bar is driven by the lawnmower wheel. L4 rotates a shaft that drives the fan gears.
FAN MECHANISM
The rotation created by the four-bar now needs to speed up again to drive a fan. This speed increase is accomplished via three Roomba gears of decreasing diameter (Fig. 6). The tiny fan represents the output rotation because I was already worried about putting the Roomba back together and I didn't want to take apart a real fan.
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Figure 6: Roomba gears are driven by the four-bar and increase the speed to drive a fan.
1. Introduction 2. Design Considerations 3. Kinematics 5. Results & Discussion