There are some inventions that seem completely meaningless to the untrained eye: who would ever need a motorized garbage can, an electric pencil sharpener or a battery powered eraser? Often, it turns out that there are some special uses where such tools make perfect sense, as in the case of motorized erasers. A small rubber spinning at high speeds gives artists and drafters a way to erase or lighten their drawing bits very accurately, which is almost impossible to do with a regular eraser.
[Franklinstein] However, he decided to design a high-speed eraser, combined with a mechanical pencil, that would return the whole idea straight to the meaningless section, though not without demonstrating his advanced engineering skills. The Eras-O-Matic has a tiny electric motor derived from a quadcopter with a very small lithium-ion battery and a power switch. The spinning bit is held by a small bearing, the whole setup of which is covered by a machined aluminum housing.
Experiments with a laser tachometer show a rotational speed of about 30,000 RPM, which is almost three times faster than a commercial electric eraser. And although it has a very good removal function, it also removes its tip in a few seconds, so a little less speed can actually make this device more efficient. If you are planning to make one of these, you may want to read our primer on small DC motors first.