The device is built upon the 5,000-year-old button spinner toy. The toy is easy to make and use: take a relatively round, thin disc and put 2 perforations in it (a flattened beer bottle cap with 2 holes punched through the middle works well), snake a thread through one hole, snake it back through the other, and tie the two ends together. Now one can put a finger through the two ends, get the disc around the middle of the loop, wind it up, and pull. The disc unwinds, and if the pull force is removed when the button is unwound, inertia will cause it to rewind. The user can pull again, and the disc spins in the opposite direction. After a brief ramp up, the toy can spin very fast -- up to 200,000 rpm -- orders of magnitude faster than any other human-powered spinner!
Despite the simplicity in the construction and operation of the toy, the physics behind it is deceptively complex. Initially as a senior undergraduate thesis and now as a larger research project led by researchers in Brown University’s Applied Mechanics Lab, we are developing an accurate, analytical model of the device. It accurately predicts the angular velocity of the spinning disc as a function of input force through time (given empirical measurements of all constants, such as disc dimensions, moment of inertia, string length, string stiffness, etc.). Such an analytical model has never been devised for the button spinner. It is powerful in that it enables us to easily optimize the device parameters for any design goals we are interested in.
Electricity generator adaptation
Equipped with this analytical model, we can adapt the device to be an electricity generator with high power output and minimal mass. By optimizing the parameters of the button spinner using the analytical model, in conjunction with the configuration of a 3-phase axial induction generator using EMWorks, we are able to make an efficient electricity generator that is differentiated in its portability, simplicity, and its input: cyclic translational motions.
How does it work?
The device consists of four core stages:
In addition to being operated by human hands, our device can also be configured to harness energy from cyclic translational motions of ocean waves, river currents, and wind. This would allow someone to generate electricity without using their own muscles.