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Before history, there was the bow. Before the bow, however, was the atlatl. This small spear throwing stick could increase the mechanical advantage of the wrist be a ratio of 6:1. The bow eventually won out due to its increased accuracy over long distances.
Well, what would it look like to create a bow with the mechanical advantage of an atlatl?
Professional and engaging intros aside, the question that actually began this project was, “How far can I launch this grape?”. I became obsessed with trying to construct an overly engineered solution to my “problem”, and at the end of my labors happened to notice the parallel in what I had built and the worlds oldest social distancing tool.
$300 and 7 Home Depot trips later, this is what I ended up with. And boy let me tell you, this thing could launch a grape. Probably. Unfortunately it never got to, because I never went to the store to get some. It did however nearly send a classmates’ eos chapstick into orbit.
Once I noticed a similarity to the atlatl, I started to wonder how I could make this device handheld. I realized pretty quickly that I would need to mirror the design to adequately balance out the forces it would put on your hands. Once I realized that, the next step was pretty obvious.
The bow features two sets of articulating linkages as opposed to one piece of flexible material. In the final design, the energy is stored in composite U springs that also act as dampers when the bow is fired.
The linkages feature a class 3 lever (left) with a class 1 lever (right) directly on top of it. This means that with a linear input force on the class 3 lever, the load point on the class one lever will accelerate.
This is what the final design looks like when drawn. Kinda cool, right?
And here is an anatomy diagram of the bow in all of its glory. This however is the original design which sourced off the shelf springs as opposed to the custom U-shaped ones in the final.
This was the final model that I made, it does not shoot very far because it was 3D printed, and no that is not a real arrow because I wasn’t legally allowed to have one for this shoot. Bummer. The model took a few months to finish, but the joy of holding it in my hand almost made it all worth it.