This spinning water contraption is actually a functional battery

If you ask someone to think of a battery, they’re probably going to picture a chemical battery, like a AA alkaline or a rechargeable lithium-ion battery. But there are other kinds of batteries that store energy without any fancy chemistry at all. If you find a way to save energy for later, you have a useful battery. Erik, of the Concept Crafted Creations YouTube channel, achieved that by storing kinetic energy in a spinning flywheel weighted with water.

This isn’t a crazy idea, because flywheels exist specifically to store kinetic energy in a spinning mass. In this case, most of that mass comes from tubes full of water. Water is cheaper than something like cast iron and it is easy to adjust the levels to maintain perfect balance.

But this wet flywheel has another trick up its sleeve: adjustable moment of inertia. Watch an ice skater as they tuck into spin and you’ll understand this. By pulling their arms and legs close their axis of rotation, the skater can reduce their overall moment of inertia and increase their speed. Erik’s flywheel can do the same thing by actuating the cylinders of water to bring them in closer to the rotational axis.

To control that process, Erik used an Arduino Nano board housed in a simple laser-cut box with a potentiometer for adjusting speed, and buttons to control power and the arm actuation. A beefy brushless DC motor spins up the flywheel under power. Then, when it is time to collect that power (such as to power the lightbulb Erik used for demonstration), that motor acts as a dynamo, like in a generator. 

As a battery for long-term power storage, this isn’t very practical. In a vacuum with perfect frictionless bearings, it would be. But in the real-world the flywheel will slow down on its own in short order. Even so, it is still a great illustration of the concept.