1 Generate Your Blueprints Choose your bottle, then let the generator draw your turtle's wooden parts.
Every Hope Turtle starts with a bottle. The wooden frame — the 6FC Ecojoiner core, the rear fin, the ballast fin and the sails — is sized around the exact bottle you'll be using, so pick one you can find plenty of locally: a sturdy, straight-sided PET bottle (1.5 L is our reference) whose cap and collar are consistent from bottle to bottle. You'll need one for the control bottle and several more for food.
Measure it carefully with calipers — diameter, height, cap, collar and the tapers at the top and bottom — then enter those numbers into our Turtle Generator, along with the thickness of the boards you'll use. The generator is 100% algorithmic: it applies the turtle_body design rules to your measurements and hands back a set of files for each component.
| Method | File | How it's used | Recommended |
|---|---|---|---|
| Carpentry | Print the carpenter sheets: every part dimensioned, with hole positions and quantities. Mark them out on your boards and cut with hand or power tools. | ||
| CNC routing | DXF | 1:1 vector outlines with holes. Import into your CAM software, set your toolpaths and route the parts from sheet stock. | |
| Laser cutting | SVG | 1:1 outlines for a laser cutter (or printed as full-size paper templates). Needs a powerful laser for 12 mm boards. | |
| 3D printing | SCAD | The parametric OpenSCAD model. Open in OpenSCAD to preview the parts in 3D, tweak them, or export STL for printing. | Not ideal because organic material can't be used. |
2 Fabrication Turn your blueprints into real wooden parts.
Carpentry
Our recommended path, and the one the whole design is built around. All you need is a saw, a drill, a ruler, a square and some clamps — tools you can find easily no matter where you are on Earth! Print the PDF carpenter sheets, mark each part onto your boards (pallet wood and offcuts work well), cut, then drill the holes. It's slower than a machine and asks for care with your measurements, but it costs next to nothing, needs no electricity beyond a drill, and anyone can learn it. Cut one test joint first to check the fit with your bottle before cutting the full set.
CNC routing
If you have access to a CNC router — at a makerspace, a sign shop or a furniture workshop — the DXF files will give you fast, perfectly repeatable parts, which is ideal if you're building several turtles. Import the DXF into your CAM software, set tabs so parts don't fly loose, and compensate for your bit diameter on the inside slots. The downsides: the machines are expensive, need some CAM know-how, and want flat, consistent sheet material like plywood rather than reclaimed boards.
Laser cutting
A laser cutter gives crisp, precise edges straight from the SVG files and is great for prototyping at small scale — try cutting the parts from cardboard or thin ply to check your fit. But the turtle's structure is designed around 12 mm boards, which most hobby lasers can't cut through cleanly; you'll need a high-power CO₂ machine, and you'll get charred edges that should be sanded. Laser-printed paper templates are a good hybrid: cut them out and trace them onto wood for carpentry.
3D printing
Technically possible — you can export STLs from the SCAD files. However, a plastic structure goes against the turtle's regenerative, mostly-organic design. Use the SCAD model instead to preview and customise your design in OpenSCAD. Save your printer for the small, precise parts of Step 5, where it truly shines.
3 Assemble Your Ecojoiner Lock your wooden parts together into the 6FC frame that holds the turtle's bottles.
The 6FC Ecojoiner is three interlocking squares of slotted boards, fitted together at right angles with no glue and no nails. Each square is two Long Johns crossed by two Little Johns, their slots locking into one another. Build them one at a time, in order, and the frame closes itself around the last piece.
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1 Lay out your pieces
Clear a table and lay everything out so you can count it before you start. You'll need:
- 6 Long Johns — a centre hole and nothing else.
- 5 Little Johns — a centre hole plus two small bolt holes at each end.
- 1 Master John — looks just like a Little John, but its two slots are cut deeper (it's stippled in these drawings).
- 4 Final Keys — the short, plain bars that lock the finished frame together.
- 24 M5 bolts, 30–35 mm long — socket-head cap screws, two for each end of every Little and Master John.
- 24 M5 metal acorn nuts — dome-topped cap nuts that thread onto the bolt tips; the smooth dome is what presses against each bottle.
Sand off any splinters at the slots, and keep a 4 mm hex key (to fit the bolt heads) and a mallet to hand.
Long Johns
Master John
Little Johns
Keys
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2 Set aside the bolts and the Master John
Look for the Master John. It's the one piece with extra-deep slots — lay it beside a Little John and the difference is easy to see. It's the very last piece you'll use, so set it to one side, and mark it in pencil if you like, so it can't get mixed up with the others.
Put the bolts and acorn nuts aside too: you won't need them until the end. If you're buying them, you need 24 of each — M5 bolts, 30–35 mm long, with a socket (hex-key) head, and M5 metal acorn nuts, the dome-topped kind.
Little John
Master John
M5 acorn nut
M5 bolt, 30–35 mm
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3 Assemble the first square
Pick two Long Johns and two Little Johns. Stand the two Little Johns on their long edges, parallel to each other, slots facing up. Turn the Long Johns slots-down and lower them across the Little Johns so each slot drops into its partner. Press or gently tap each joint until the edges sit flush. You now have a square with four arms reaching out past the corners — those arms are the ports your bottles will slide into. If a joint is too tight, sand the slot rather than forcing it. Sometimes it helps to tap it into place with a mallet — but never use another John to tap: the blow often snaps a John at its slot cuts.
Long Johns ×2
Little Johns ×2
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4 Add the next square
Grab two more Little Johns and one Long John. Assemble them into a U shape. Slide the U into the centre of the square you've already got assembled — the two protruding Johns should slide nicely into the square's centre. Then, grab one more Long John and complete your U into a square.
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5 Place the final square
The third square uses the last two Long Johns, the last Little John — and the Master John. Fit the Long Johns and the Little John first. The frame is now almost closed, and a standard John would no longer fit past the boards already seated; that's what the Master John's deeper slots are for. Slide it in last, slots first, and work it into place until it springs home and sits flush with the rest.
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6 Add the keys, bolts and acorns
Slide the four Final Keys lengthwise into the frame, one into each of the four corner channels around its centre, until they sit centred — they lock the three squares so they can't spring apart. Then fit the bottle clamps: each Little and Master John end has two small holes, 24 in all. Drive an M5 bolt into each hole from the outside with your hex key; the hole is sized so the thread bites into the wood, so go slowly and keep it straight. When the tip pokes through into the port, run an acorn nut all the way onto it, then back the screw off so the port is clear for its bottle. In Step 7 you'll tighten them until the acorns press each bottle firmly in place.
Fitting the rear fin or ballast fin? Their boards fill a port and bolt through the John with these same screws, so leave the acorns off those ports.
4 Assemble Sail Components Build the fins and sail frame that turn your Ecojoiner into a full turtle.
Once your ecojoiner is assembled, you can move on to generating the sail components that we add to the ecojoiner to make it a full-fledged turtle! Use the turtle generator to create the carpentry or cutting files for your bottom ballast fin, rear fin, front fin and sail apparatus, then make these in the same way that you cut your ecojoiner. Assemble them as follows…
Bottom Ballast Fin
Six pieces: two core slats, a bottom board, two lock feet and the ballast fin. Stand the two core slats upright in the bottom board's two outer slots, so their M5 hole pairs end up at the top. Slide the ballast fin into the deeper centre slot between them, so the slot in the fin and the slot in the board interlock. Then push a lock foot into the slot at each end of the board to hold everything square. Later, the top of each core slat bolts flat against a Little John of the Ecojoiner's bottom port with an M5 pair, just like the Ecojoiner's own clamps.
Rear Fin
Four pieces: the rear fin, two bottle-holder shafts and the solar-panel holder. The fin's front edge has two slots and each shaft has one at its rear end; they meet halfway, so lay a shaft flat into each of the fin's slots and press the half-lap joints together until the edges sit flush. Then drop the solar-panel holder onto the notch at the top of the fin, crosswise, so it can carry the panel. The front end of each shaft carries an M5 hole pair that bolts against a Little John of the Ecojoiner's back port, with the fin holding the bottle in its port.
Front Fin
Three pieces: the front fin and two head fin slats. It's the rear fin's mirror on the front port — the raked fin's rear edge has two slots and each slat has one at its outer end, so slide the two slats into the fin with half-lap joints until they sit flush, one above the other. The other end of each slat bolts against a Little John of the Ecojoiner's front port with an M5 pair, so the bottle sits between them. The front fin is still experimental, so let us know how yours goes.
Sail Apparatus
The sail frame stands on the control bottle's cage (Step 5). Its two tall sail battens have a two-layer notch at the top: lay the sail crossbar connector into those notches first, then set the two top sail bar halves on top of it and fix each one to the connector with an M3 screw. The connector's centre hole takes the sail shaft, which a side M3 clamps in place. Slot a bottom sail bar into the lower slot of each sail batten, sit a joint strengthener on each bar beside its batten and bolt it through with an M6. The two shorter non-sail battens stand at right angles, each with a C end piece in its lower slot, and all four battens fix to the cage with two M3 screws each. Finally, staple the sails' fold-over tabs to the top bar halves and the bottom bars.
5 Build Your Control Bottle 3D-print the turtle_body v1 parts that turn a bottle into the turtle's steering heart.
The control bottle is the one bottle in your turtle that holds no food: it holds the electronics and drives the sail. Its parts need precision and waterproofing that wood can't give, so they're 3D-printed from the open-source turtle_body v1 STL files. Here's what you'll print:
- The turtle cage The rotating cage that sits on top of the control cap and rides on eight bearing bumps. The sail battens bolt into its grooves, so when the cage turns, the sail turns.
- The control cap The large stationary disk that seals into the cut-open control bottle. Its central bore carries the sail shaft through an O-ring gland, keeping the electronics inside dry.
- The O-ring seal moulder A two-part press mould for casting your own silicone seals: the flat rings that seal the cap insert to the bottle, and the small O-rings that seal the spinning shaft.
- The shaft The round axle that connects the sail cage to the inside of the bottle. A magnet in its lower end lets the turtle's angle sensor read exactly where the sail is pointing.
- The gear chassis Coming soon The internal frame that will hold the motor and gearing that turn the shaft and steer the sail.
These files are currently sized for our reference bottle. We're building a tool that will generate them for your bottle.
6 Assemble Your Circuits Pull together the turtle's hardware stack on its Turtle Shell.
Now for the turtle's brain and nervous system. The hardware stack is built around a Seeed XIAO ESP32-S3 microcontroller, joined by a GPS module, a real-time clock, a battery and power monitor, the magnetic angle sensor that reads the sail shaft, the motor driver that turns it, and a small solar panel to keep everything charged. All of it plugs into the Turtle Shell — our open-source printed circuit board that connects, powers and protects the electronics so they can be tucked neatly inside the control bottle.
There are two ways to get your Turtle Shell:
- Order a shell from us Coming soon A ready-made Turtle Shell, shipped to you from the Hope Turtle Project.
- Commission your own The Turtle Shell's plans are fully open source. Send the Gerber and pick-and-place files to a PCB manufacturer such as JLCPCB or PCBWay in China and have a batch printed and assembled to order.
With your shell in hand, solder on the headers, seat the XIAO and modules, connect the battery, solar panel and motor leads, and test that everything powers up before it goes into the bottle.
7 Put It All Together! Wood, bottles, printed parts and circuits become one turtle.
This is the moment it all becomes a turtle. Gather your 6FC Ecojoiner from Step 3, the fins and sail frame from Step 4, the control bottle parts from Step 5 and your Turtle Shell from Step 6, then bring them together in five steps.
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1 Assemble the turtle body
Bolt the three fins onto the Ecojoiner. The ballast fin goes on the bottom port: push its two core slats into the port, one inside each of the port's Little Johns, until their tops sit flush with the frame, then bolt each slat to its John through their matching M5 hole pairs. The rear fin goes on the back port in the same way, its fin pointing down and its solar-panel holder on top, and the front fin on the front port, opposite it. Each port's bottle will later slide in between the two slats, its base resting against the fin.
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2 Add the circuits to the control bottle
Lower your tested Turtle Shell, with its battery and sensors connected, into the cut-open control bottle. Pass the sail shaft through the control cap's central bore, with its O-rings in the gland and the magnet end inside so it sits over the angle sensor. Then press the control cap into the bottle's open end over the flat silicone rings so the electronics are sealed in and dry.
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3 Add the control bottle and sails
Slide the control bottle neck-first into the Ecojoiner's top port, control cap facing up, and tighten that port's two M5 cap screws until their acorn nuts hold it firmly. Set the cage on the control cap, then lower the sail frame onto it so the shaft rises through the crossbar connector. Fix each of the four battens to the cage with its two M3 screws, and tighten the connector's side M3 onto the shaft so the sail turns with it.
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4 Add the aid bottles
Slide a bottle neck-first into each of the five remaining ports and tighten the two M5 cap screws at that port's end until their acorn nuts press the bottle firmly in place. For a test build, use empty or water-filled bottles; you'll pack them with food in Step 9.
Drawing coming soon -
5 Add the turtle labels
Label your turtle so that whoever finds it knows what it is, where it came from and what to do with it. Our label designs and guidance are coming soon.
Before your turtle goes anywhere near the sea, check every bolt, spin the sail by hand to make sure it moves freely, and float-test it in a bucket, pool or calm water.
Drawing coming soon
8 Set Up TurtleOS Give your turtle its brain — and connect it to your hopeturtles.org account.
TurtleOS is the open-source navigation software that runs your turtle. To install it, you'll need a free Buwana account on hopeturtles.org. Log in, register your turtle from your dashboard, and you'll be given its device ID and device key — the credentials your turtle uses to report its position back to this site.
Then plug your XIAO ESP32-S3 into your computer by USB and run the TurtleOS install script in a terminal. It will walk you through flashing MicroPython, then ask for your wifi details and your device keys, write them into your turtle's configuration and install the latest TurtleOS. Keep your device key private — it's what proves to hopeturtles.org that your turtle is really yours.
9 Pack Your Food Bottles Fill the rest of the turtle with something worth delivering.
The rest of the turtle's bottles are its cargo — and its buoyancy. Wash and fully dry each bottle (any moisture left inside will spoil the food), fill it with a dry good, and seal the cap tightly. A strip of tape or a dab of wax over the cap adds an extra seal against the sea.
Dry goods that work well:
- Rice
- Lentils and dried beans
- Flour and cornmeal
- Sugar and salt
- Rolled oats
- Small pasta
- Coffee and tea
- Powdered milk
- Nuts and dried fruit
- Spices
The key is to pack every bottle tight. Fill a little, then tap and shake the bottle to settle the contents, and repeat until it's packed right to the top with no air gap. A tightly packed bottle is rigid and strong, keeps its shape against the waves, can't slosh or shift the turtle's balance, and leaves no room for air and moisture to spoil the food. A loosely packed bottle dents, rattles and rots.
10 Download the Turtle Wrangler Your turtle's remote control, in your pocket.
The Turtle Wrangler is our Android app for working with your turtle in the field. It will be available on the Google Play Store soon.
Standing next to your turtle, open the Wrangler, connect to it, and set its two most important coordinates: its Departure — the point it's setting out from — and its Destination, the shore you want it to reach. Pick each one on the map or drop a pin at your current location. The Wrangler sends them to TurtleOS, which uses them to steer the sail toward the destination for the rest of the journey. Then check your turtle's battery, GPS fix and sail sensor before you say goodbye.
11 Deploy or Deliver Set your turtle free yourself, or send it to join a flotilla.
Deploy it yourself
Wait for a windy day when the wind is blowing steadily from your departure point toward your destination — check a local wind forecast, and never launch into an onshore wind that will push your turtle straight back to the beach. Make sure your turtle is powered on and has a GPS fix, carry it out past the breaking waves (by kayak or boat if you can), point it downwind and let it go. Stay a few minutes to watch it find its course.
Deliver it to a flotilla
Not near the right coast, or want your turtle to travel with others? Pack it up — remove the sail and fins, wrap the control bottle to protect the electronics, and box the parts securely — then deliver or ship it to a flotilla reception point. There it will be checked, reassembled and launched alongside other turtles on a community arribada mission, all setting out together toward the same destination.
12 Track Its Progress Follow your turtle across the water.
Once your turtle is swimming, it will report its position, battery and sensor readings whenever it can connect. Follow its journey live on hopeturtles.org — from your dashboard or on the mission map — or in the Turtle Wrangler app. And when your turtle reaches shore, whoever finds it can report the arrival here, closing the loop on its journey.
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Now make it better.
Found a better joint, a better seal or a better bottle? Every part of the Hope Turtle is open source — share your improvements on GitHub and help the next builder.