week 1: computer-aided design

Overview

Our first assignment was to model and design our final project. For me, the largest hurdle and the step I spent the most time on was actually choosing a final project— after days of agonizing, I was struck by a moment of whimsy, and decided on the humble peashooter.

Design Goals

• I wanted it to look like a peashooter - very little else to say there.
• I wanted it to shoot something relatively small and nondangerous, but definitely larger than a pea. I decided on ping-pong balls.
• I wanted it to be able to shoot automatically continously without human input - hence we need some sort of reload mechanism.

2D Design

I like drawing out my designs first. Here are some initial sketches I did.

I have very little experience with designing mechanisms, so I tried to stick to things that a) I could intuitively understand, and b) would fit within the form of a peashooter. The shooting part needed to be compact and reloadable, so I settled on a sort of friction-wheel mechanism I’d seen before, and added gears until a motor would fit. The feeder mechanism needed to fit into the stem, so I went with a spiral lift mechanism. The base just needed to feed into the spiral lift, but I didn’t want it to be a point of failure, so I decided on making it a solid, static block with a spiral track that would reliably feed balls into the lift.

To help design the shooting mechanism, I drew an isometric drawing of the gears - as squares, because circles are hard to figure out in perspective.

And since I’d found the isometric paper template already, I also drew the full peashooter with some dimensions I thought I might want to consider or paramatrize (spoiler alert: I did not stick to these)

And then I could no longer procrastinate the part I dreaded: the CAD

3D Design

I have CAD experience, but I never considered myself very good at it. Fusion, too, was a software I’d barely touched before, but as a lot of the class supports it, it seemed prudent of me to use it too.

I first started with the ping pong ball that I was basing all my sizing around:

Then created the shooting mechanism around it with help from Fusion’s helpful spur gear script (and some randomly selected angled gears from McMaster-Carr)

And then played with the coil tool and some strategic sweeps to make the feed mechanism.

Then struggled an unexpected amount with trying to make the base - first with trying to make the spiral before I discovered 3D sketches, and then with trying to make a well-constrained and nice-looking 3D sketch that the sweep tool would accept as valid.

But then I put it all together and added some quick revolves to get:

Behold! A peashooter!

Final Thoughts

I expect to have to rethink, redesign, and remodel the mechanisms once I do some testing or actually learn how they work. I’m okay with this. Everything is also still just… floating, but I think I can figure out supports and assembly once the design is more fixed.