Quarter Sub - AKA Cartesian Diver

by Rapslogan, published

Quarter Sub - AKA Cartesian Diver by Rapslogan Jul 3, 2015
0 Share
Download All Files

Thing Apps Enabled

Order This Printed View All Apps


Liked By

View All

Give a Shout Out

If you print this Thing and display it in public proudly give attribution by printing and displaying this tag.

Print Thing Tag

Thing Statistics

4319Views 758Downloads Found in Physics & Astronomy


A simple toy to demonstrate Archimedes principle and Boyles law.

Archimedes principle states that a body immersed in a fluid experiences a buoyant force equal to the weight of the fluid it displaces. Using Boyle's law we then change the amount of fluid displaced to make the quarter sub rise and fall. This is achieved by simply squeezing the bottle which reduces the volume of air in the main chamber due to an increase in pressure and this in turn reduces its buoyant force (Boyle’s Law).



Parts required:

  • The main chamber (8.2cm^3) Internal air cavity volume 11cm^3
  • The basket (1.4cm^3)
  • Displacement plugs (1 cm^3)
  • A semi ridged bottle with good lid
  • A couple of US Quarters or other weight.

This is a 3 part print. All parts are designed to be scaled and can be printed without a raft or any support material. For the Quarter Sub to work the main chamber must be sealed and not allow air to be squeezed out. I have used the following settings:

  • ABS or PLA 100% fill at 0.2mm layers
  • ABS 80% fill at 0.2mm layers using an Acetone rinse to seal the chamber.

The Experiment and Fine Tuning:

  • Print the parts as above.
  • Add a weight: 80% fill ABS 2 US Quarters (11.3 Grams); 100% fill ABS or PLA 1 US Quarter (5.7grams).
  • Fill the bottle with water, gently drop the Quarter Sub in then close the lid.
  • Squeeze the bottle to see the Quarter Sub Drop and release to watch it rise.
  • If the Sub sinks use less weight. If it requires too much force or won't sink then you will need to add some displacement plugs. These will be required for ABS at 100%. Some trial and error may be required here.

The Math:
The buoyant force of the Quarter Sub:

Fb = pfluid Vsubmergedg

In the system pfluid and g remain a constant. To change Vsubmerged we use Boyle's law which in short states: assuming the temperature of the gas does not change when the volume is halved, the pressure is doubled; and if the volume is doubled, the pressure is halved.

V submerged(For the air) = P1V1 = P2V2 because we have a closed system V1 is constant therefore V2 = (V1P1)/P2.

So by squeezing the bottle P2 increases and the volume of air in the chamber is reduced therefore the Quarter sub will begin to sink. Releasing the pressure increases the volume of air and restores its original buoyant force.

For the record my 3 year old couldn’t care less about the math but loves to make the sub rise and fall.

Density of PLA aprox 1.25 g/cm^3
Density of ABS aprox 1.04 g/cm^3

More from Physics & Astronomy

view more

All Apps

Auto-magically prepare your 3D models for 3D printing. A cloud based 3D models Preparing and Healing solution for 3D Printing, MakePrintable provides features for model repairing, wall thickness...

App Info Launch App

Kiri:Moto is an integrated cloud-based slicer and tool-path generator for 3D Printing, CAM / CNC and Laser cutting. *** 3D printing mode provides model slicing and GCode output using built-in...

App Info Launch App
KiriMoto Thing App

With 3D Slash, you can edit 3d models like a stonecutter. A unique interface: as fun as a building game! The perfect tool for non-designers and children to create in 3D.

App Info Launch App

Print through a distributed network of 3D printing enthusiasts from across the US, at a fraction of the cost of the competitors. We want to change the world for the better through technology, an...

App Info Launch App

Quickly Scale, Mirror or Cut your 3D Models

App Info Launch App

Treatstock is an online platform that offers decentralized manufacturing services such as 3D printing and CNC machining for business-to-business and business-to-consumer sales all over the world. W...

App Info Launch App

3D print your favourite design with NinjaPrototype, a professional 3D manufacture with consistent quality and speed.

App Info Launch App

Hi 4Muel8.

I too played with one as a kid although I never knew the name. To me it was just a cool pen cap with a blob of blue tack that I could make float or sink. When my daughter started to learn about objects sinking or floating I started to think about it again. This lead to the development of the Quarter Sub and the refinement for Thingiverse. I have now updated the name. Thanks.

The original concept used NZ 10c coins but these are kind of rare outside of NZ. So i tweaked the design for the more accessible US quarter.

FYI if anyone wants a custom design for the base let me know. Its pretty easy to modify.

They were a lot of fun! Mine came as a small kit with a plastic eye dropper and brass nut as the main part, with a rubber cover to pull over it to make it look like a squid.

Ah, a cartesian diver! I had one of these as a kid! They also demonstrate Pascal's Law (transmission of fluid pressure in a confined space). Your design is well executed.

haha, why's a guy with a New Zealand accent designing for US quarters!?