Power Up Your Pencil With The 30,000 RPM Erase-O-Matic

An electric eraser built into a mechanical pencil

There are some inventions that look completely pointless to the untrained eye: who would ever need a motorized garbage can, an electric pencil sharpener or a battery-powered eraser? Quite often, it turns out that there is some niche use case where such tools make complete sense, as is the case for motorized erasers. Having a tiny piece of rubber spinning at high speed gives artists and drafters a way to very precisely delete or lighten bits of their drawing, something that’s nearly impossible to do with a regular eraser.

[Franklinstein] however decided to design a high-speed eraser integrated into a mechanical pencil that brings the whole concept straight back to the pointless category, although not without showing off his advanced engineering skills. The Erase-O-Matic contains a miniature electric motor sourced from a quadcopter, together with an ultra-small lithium-ion battery and a power switch. The spinning bit is held by a tiny bearing, with the whole setup covered by a machined aluminium housing.

Tests with a laser tachometer show a rotational speed of about 30,000 RPM, which is almost three times as fast as a commercial electric eraser. And although it has very good erasing performance, it also wears out its tip in a few seconds, so a bit less speed could actually make this device more useful. If you’re planning to build one of these yourself, you might want to first read our primer on small DC motors.


20 thoughts on “Power Up Your Pencil With The 30,000 RPM Erase-O-Matic

  1. The youtube “thing” these days seems to be somebody with an absurd expression holding up whatever gadget they have brewed up. I am hoping this will pass soon. It sort of reminds me of the joke. What are a red-necks last words?

    “Hey y’all — watch this”

    1. The algorithm loves people pulling funny faces for some goddamned reason; I assume it drove itself into a culdesac based on young kids frantically clicking on videos with those kinds of thumbnails.

      1. Sensationalism and hyperbole are proven methods for getting views, it’s not necessarily limited to kids. You can see the same thing taking place at mainstream news outlets like CNN.

        Mostly it’s just a sign that the platform is in decline. The new, hip platforms don’t need to resort to dirty tactics for clicks because viewers will just flock to them simply because they’re seeking refuge from other platforms. Then the tactics will just happen to them again once a majority of the audience has been captured.

        1. you mean a gag with an open mouth ring is secretly trying to get views from the bdsm crowd?

          society is in decline because we optimize for profit and efficiency, rather than quality and harmony.

          it all comes down to what you optimize for, and our society optimizes for perceived profits, when they’re actually just ruining the best things about life for literally all but a handful of people.

    2. A YT’er I follow has absurd titles that often have nothing to do with the video. He even made a video about the titles. He explains in the video that the YT algorithm demands this from the makers, as that’s the way the algorithm works. If he doesn’t do that, his video’s aren’t put at the top of peoples feeds, but pushed further back. He even said he didn’t like it. A video titled “You won’t believe how insane this is!!!” gets a ton more views than “Beautiful working saw mill from 1957” even if it’s the same video.

  2. I ‘member seeing powered erasers in the 80s or 90s, aimed at draftsmen really I think (So before AutoCAD was “everything”) and a tad bigger, needing something like a Mabuchi 360 and a few C cells in.

    1. Heh, been around a long while it seems, at least in corded versions… went looking for the ones I remember, and not seeing them.. hard to tell whether there was a 21st century resurgence in use the last few years, or they’ve always been a subsurface nichey niche all along. Anyhoo, some of the real early corded ones are looking like they went down to the factory floor sometime in the 1940s, snatched up an electric wrench and minimally modified it to hold an eraser :-D

    2. I took drafting in high school about 1975. Nothing about schematics, all about buildings. But I think I knew about electric erasers then. Can’t remember why. Maybe tgeteacher had one.

    3. They’re still around. The Sakura Electric Eraser (with Sumo Grip) is targeted at the manga/comic book crowd. They’re also useful for removing price tag glue from book covers without damaging them.

  3. When I was a little boy I would take electric motors out of toys and stick an eraser on the end and erase the teeth out of magazine pictures, my older sisters hated that!

  4. My dad was an engineer before cad. he had several mechanical erasers. i used them to clean the tracks on things like train sets and slot cars. They actually worked rather well.

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