Theme 2: Bushnell

Welcome to Week 2.

Last week you mastered circuits, conductivity, and the Makey Makey. This week you take those tools underwater.

Your kit grows. Your sub grows. By the end of the theme, your pair owns one of the Turtle's five major sub-systems — and the rest of the class is using your work to make their subs better.

Theme 2 of 3

David Bushnell — The Turtle

In 1775, a 35-year-old engineering student at Yale named David Bushnell dropped out of college to build the world's first combat submarine. He named it Turtle. It had a glass viewing port, hand-cranked propellers (vertical AND horizontal — he invented the screw propeller for it), real ballast tanks pumped by foot pedals, and a screw on top designed to drill into the hull of British warships and attach a 150-pound gunpowder bomb.

It was used in combat on September 6, 1776, in New York Harbor. Sergeant Ezra Lee piloted it solo against the British flagship HMS Eagle. The mission failed — the drill couldn't penetrate the hull (probably copper-plated) — but the British were spooked enough to move their entire fleet. One person, one sub, one near-miss that changed the war.

This week, you build your own.

🌊 Submerge

Today's mission is simple but hard: make a plastic bottle sink, float, and hold a specific depth. No tricks. Just balance.

History spotlight

Bushnell's Turtle controlled depth with ballast tanks — chambers that filled with water to sink, then emptied with foot-pump pressure to rise. Same physics as your bottle today. Things float when they push enough water out of the way to support their weight. Add ballast, the balance shifts, the sub goes down.

Instructions

Part I: Build the basic submersible

Materials at your table

1 plastic bottle with cap (16–20 oz)
Modeling clay (about a golf ball's worth)
Waterproof tape
Scissors
A permanent marker (for labeling your sub — every sub gets a name)

Fill your bottle about a third full with water and put the cap back on. This is your starting ballast.
Press a wad of clay onto the outside of the bottle. Start small.
Wrap waterproof tape around the clay to hold it in place.
Name your sub. Write the name on it. (Bushnell named his Turtle. You're allowed to do the same.)

Instructions

Part II: Test sink / float / hold

Take your sub to a water bin. Set it carefully on the surface. Three possible behaviors:

Floats — not enough ballast. Sits on the surface.
Sinks fast — too much ballast. Hits bottom.
Hovers — neutral buoyancy. Hangs at a depth. This is what you want.

In your 📓 Inventor's Notebook, predict what your sub will do before you put it in the water. Then test. Did your prediction match?

Instructions

Part III: Hit neutral buoyancy

Adjust clay or water until your sub hovers in the middle of the bin without rising or sinking. This is the goal.

The trick: Small adjustments matter. Adding a pea-sized piece of clay can change everything. Patience.

Once it hovers, leave it in the water for 60 seconds. Watch what happens. (Does it slowly drift up or down? Why?)

In your 📓 Inventor's Notebook, record how much clay it took to reach neutral buoyancy, and note any drift. Sketch your sub with its ballast clearly marked.

🌊 Specialize

Yesterday every pair built the same thing. Today you pick what to be the world's expert at.

The Turtle had five major sub-systems. Each one was someone's job to figure out. Today you pick one and become Bushnell.

Instructions

Part I: Pick your specialty

Read all five. Discuss with your pair. Pick one.

⚖️ Buoyancy & Ballast

Your job: make your sub change depth on command. Sink to the bottom, hover mid-water, rise to the surface — repeatedly, predictably.

Bushnell connection: foot-pump ballast tanks. Materials to think about: clay, syringes, balloons, tubing.

🛡️ Hull Integrity

Your job: make your sub water-tight at depth. Modify the bottle (cut a port, add a window, add hatches) — and seal it so nothing gets in even after a full minute submerged.

Bushnell connection: the Turtle's wooden hull was waterproofed with tar and iron bands. Materials: bottle, waterproof tape, hot glue, scrap plastic for windows.

🌀 Propulsion

Your job: make your sub move under its own power. Forward, sideways, anywhere. Bushnell invented the screw propeller for the Turtle. What will you invent?

Bushnell connection: hand-cranked propellers, one for forward thrust and one for vertical movement. Materials: rubber bands, propellers/paddles, balloons, weighted ramps.

Instructions

Part II: Plan your upgrades

Open your 📓 Inventor's Notebook to the Specialization Role Page. Fill it in with your pair. This page comes with you for the rest of the week.

Answer with your pair:

What's your specialty's one job?
What materials will you need?
What does success look like by the end of this theme?
What's your biggest worry?

Instructions

Part III: Start building

Head to the materials table. Grab what you need. Start modifying your sub.

Don't lose your neutral buoyancy. Whatever you add today, your sub still needs to behave in water. Test in the bin every time you make a major change.

Get a working version of your upgrade by the end of class. Tomorrow is the mission. You'll need everything functional.

🌊 Mission

September 6, 1776. Sergeant Ezra Lee climbs into the Turtle in New York Harbor and pedals it toward the British flagship. He has one shot at the hull, one charge to attach, one chance to change the war.

Today's your mission.

Instructions

Part I: The base mission

Every sub must:

Submerge — descend from the surface to the bottom of the bin within 20 seconds.
Hold — stay at the bottom for at least 10 seconds.
Surface — return to the surface within 20 seconds.

Instructions

Part II: Your specialty challenge

On top of the base mission, your pair has to also pull off your specialty's job:

Buoyancy: hit at least 2 distinct depths during the mission (mid-water hover + bottom).
Hull: zero water inside the bottle after 60 seconds submerged.
Propulsion: move at least 15 cm horizontally during the dive.

Instructions

Part III: Run the mission

Each pair gets three mission attempts. You can adjust between attempts — add clay, fix a leak, retie a string. But the clock runs each time.

In your 📓 Inventor's Notebook, fill in the mission data table for all 3 attempts. Note exactly what failed each time.

Don't sugarcoat your data. Engineers learn from honest failure logs, not from pretending things worked. If it sank too fast — write that. If your propeller fell off — write that.

🌊 Iterate + Sensor

Yesterday most subs failed something. That's normal. Today is split into two halves: fix what failed, then add an electronic eye to your sub.

Instructions

Part I: Fix yesterday's failures

Pull out your 📓 Inventor's Notebook. Look at your three mission attempts from yesterday. Pick your biggest failure — the one that costs you the most points.

Spend 25 minutes on it. Fix it. Test it. If it works, test it again. Don't move on until it's solid.

Tip from engineers: one fix at a time. If you change three things at once and the sub works, you don't know which change fixed it. Isolate variables.

Instructions

Part II: Design a sensor for your sub

The challenge: use your Makey Makey + Scratch to detect one event in your sub's behavior. Possibilities:

Sub reaches the bottom of the bin
Sub surfaces
Sub crosses a specific depth marker
Sub's hull springs a leak (water reaches a sensor inside)
Your own idea

This is an open engineering problem. There's no right answer. Here's what you know:

Makey Makey fires when its SPACE input is connected to EARTH through something conductive.
Foil is conductive. Water is slightly conductive (tap water more than distilled).
Foil-to-foil contact conducts way better than water alone.
You can run wires up out of the water to keep the Makey Makey itself dry. The Makey Makey must stay dry.

In your 📓 Inventor's Notebook, sketch your sensor design before building. What event are you detecting? What two pieces have to touch (or stop touching) to fire it?

Instructions

Part III: Build, test, debug

Set up the Makey Makey to fire a Scratch sound or animation. Build your sensor. Run a quick mission. Did the sensor fire when it was supposed to?

Common gotcha: tap water is conductive enough that just having your foil in water might trigger the Makey Makey constantly. If that happens, test it. Then redesign — maybe your sensor needs to be above the water line, with a wire that closes the circuit only when your sub touches a specific spot.

A sensor that fires every time is not useful. A sensor that never fires isn't either. Aim for honest — fires when the event happens, stays quiet when it doesn't.

🌊 Stealth Mission

Today: run the full mission with the class watching, and pick up ideas from what other pairs figured out.

Instructions

Part I: Mission run

Run the full mission one more time — base mission + specialty + sensor firing at the right moment. You get one attempt with the class watching.

Before you run it, take 10 minutes to set up clean. Check the sensor. Test the buoyancy. Make sure the sub still does what it did last session.

Instructions

Part II: Pair-by-pair walkthroughs

When it's your turn, do all of this:

Name your sub and announce your specialty.
Run the mission once in front of everyone.
Demonstrate your sensor firing.
Tell the room: what's the one thing you'd change if you had another week?

Instructions

Part III: Notebook wrap

While other pairs are presenting, your job is simple: listen for theft material. Other specialists figured out things you didn't.

In your 📓 Inventor's Notebook, finish the Bushnell theme wrap-up — including one specific idea from each specialty other than your own that you'd use next time.

That's Bushnell. You built a working submersible, owned a sub-system, ran missions, and put an electronic sensor on a vehicle moving through water. That last part — putting instruments on a vehicle to monitor its behavior — is exactly how every modern self-driving car, drone, and Mars rover works.

Next: Open Lab + Showcase. Time to refine your work and walk family and program staff through what you've built.

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