final project

Thinking

Wants

I’ve built a lot of little parts for quite practical things, so I wanted to make something more “useless” and whimsical. My main want:

• bring me joy

Some secondary wants:

• I wanted it to be possible to store, it has to be disassemblable, small, or physically robust.
• I wanted moving mechanical parts - they’re fun, and I have absolutely no experience designing them

Idea

I was juggling quite a few different ideas in my head, before someone suggested to me that I could make something that shoots. What’s something fun that shoots? A peashooter!

Additional Design Requirements

• must fit in the form/shape of a peashooter
• must shoot hard enough to cover a distance of, say, 2m, but not hurt someone if hit

Designing

The overall design process can then be seen from my week 1 documentation. Here is my v1 CAD:

It’s not small, it’s barely disassemblable, but I hope it will pass physically robust - everything delicate is encased, and the shell seems easy to make sturdy.

It definitely has moving parts.

This might have to largely be 3D printed. I’m thinking I could CNC-mill the base out of wood, though, which would make it more organic (suitable for a plant) and sturdy. Leaves and other decorations I think would be cool to lasercut out of clear green acrylic, and heat-gun into shape. Ping pong balls I will purchase.

Anyways, system diagram!

Focus: Shooting Mechanism

A gear chain might have been my first idea, but it likely wasn’t going to be the best one. I also sketched out the following mechanisms:

Where the summary is that:

• Two motors on flywheels would be the simplest if I just wanted something to shoot, but least satisfying to build
• A full geartrain was daunting, and I was worried about force transfer,
• Bands seemed… physically difficult, and inelegant when my rotations needed to be in opposing directions
• A spring-loaded mechanism would shoot pretty well! But given how the ball would have to be loaded and the space constraints within the head, the packaging seemed troublesome. This was the reason I wanted a flywheel mechanism in the first place.

Turns out I still couldn’t decide. I’ve always had trouble thinking of things in the abstract, so the next step was to prototype something.

Cue 3D printing week.

The gears were stiffer and louder than I expected, but worked fairly well. The stiffness could be mitigated by using bearings instead of having a plastic-on-plastic axel, but I was still worried about force transfer and the general loudness/impreciseness of plastic meshing, especially at speeds. With this in mind, I designed the sketched out the following mechanism next:

One motor, two gears, two bands.

// todo: do math - ball speed, motor speed, wheel size

// todo: cad, print, assemble, and test new shooting mechanism (with bearings!)

Focus: Spiral Lift

// todo: test print a bunch of spirals to find the min diameter one that can still print nicely + lift ping-pong balls reliably

Focus: Electronics

My input devices week implements and tests a distance-sensing system. My output devices week links these sensors to my chosen motors. Building on what I did there, I wrote the following code to activate the spiral lift whenever the shooting channel is empty and to shoot whenever someone comes within shooting range:

#include <Wire.h>
#include <VL53L1X.h>

#define RED 17
#define GREEN 16
#define BLUE 25

#define MOTORA 0
#define MOTORB 1

#define IRLED 26
#define PHOTOTRANSISTOR 27

// todo

Putting it all together

// todo: final sketches

// todo: complete CAD

Making

// todo: make

Plan to completion