An issue with using springs to propel the AEV is the fact that a spring only rotates in one direction. Because of this, a way to spin the main driving wheel in two directions needed to be found.
The first idea was to have two moving gears that would engage and disengage with a gear attached to the driving wheel. Each gear would be turned by a separate spring, spinning the gears in opposite directions. When one gear is engaged, the AEV travels forward and when the other gear is engaged, the AEV travels backward. Here is an image to illustrate this effect:
Gear is disengaged
Gear is engaged
The first problem with this design was the need for two springs. Constant force springs are somewhat heavy and so reducing this number to only one spring would be ideal. Another issue with this design is the fact that it required moving gears. As you can see from the picture above, this was solved by putting slots into the middle of each gear. This sort of solution might work, but also leaves the gear fairly unstable, and stability of this mechanism is very important. Because of these issues, there was need for a redesign.
Instead, a new design was created in which the larger driving gears would not translate, but smaller gears would be placed between the gear on the driving wheel and the larger gear being driven by the spring. With one gear between the two, the AEV would travel forward, and with two gears between, the AEV would travel backward. With this in mind, a mechanism that would allow swapping between one gear and two gears was devised. This way, there was no need for the instability of slotted gears, and there was only need for one spring. Here is an visual to illustrate this mechanism.
AEV Traveling Forward
AEV Travelling Backward
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