This DIY Stirling Engine Kit Will Stir Your Morning Coffee For You

In 1816, engineer Robert Stirling invented his proprietary Stirling engine, an automatic power source operated by ambient heat rather than direct fuel sources like an internal combustion engine. It was quite a nifty little contraption, serving as the bedrock of the steam engine concepts that followed, though it never saw widespread adoption since you still needed a source of heat to make it work, and obviously, you can't just get heat anywhere. Still, while you can't use a Stirling engine to power your car (yet), you can use one to stir your coffee.

EngineDIY's Stirling engine coffee cup kit allows you to create your own miniature Stirling engine and then mount it on top of a steaming cup of your favorite morning brew. The engine will roar to life, spinning and pumping, which not only looks really cool on your desk but also stirs your coffee and serves as a handy metric of how hot it is. The Stirling engine coffee cup kit is both an excellent conversation starter at the office and a nifty toy to teach the youngins about thermodynamics.

First, you make a fresh pot of coffee and pour it into an appropriately sized mug. Place the engine on top of the mug so it completely covers it, give it about a minute to warm up, then give the flywheel a gentle nudge. The engine will start working, and its attached spoon will stir your coffee.

The Stirling engine works thanks to air (or other gas or fluid) trapped between two metal discs. The heat under the lower plate causes the air inside to rise, lifting an insulation disc inside the engine. Two pumps are connected between the insulation disc on the inside and the flywheel on the top. When the warm air inside the engine rises and reaches the cooler top plate, the air cools and drops the insulation disc, pushing it downward and changing the positions of the pumps, thus moving the flywheel. The temperature difference between the two plates and how it affects the air inside cause the insulation disc to move up and down rapidly, spinning the flywheel on top.

It doesn't have to be coffee either; any hot liquid will do so long as it's less than 150 degrees Fahrenheit. For added fun, place an ice cube on top of the engine to increase the temperature difference and boost the speed!