Pendulum Hardiscum (Harddisc Pendulum)
German Translation

An old hard drive motor turned into a pendulum: one line of LEDs on the perpendicular to provide colorful stills, animations, text and the time.

This project is participating in the 'Mach flott den Schrott 2011' (lit. 'Pimp the Scrap') contest powered by  c't Magazin, a German computer bi-weekly.

Contest Page (German)

Contest Entry (German)

YouTube Video


A Hard drive and a pendulum? Any tech-savvy man might suspect the heads in a hard drive floating above the disks and providing us within the blink of an eye with our ever so valued data. But no, another albeit also very nimble part of the drive, it's engine, responsible for rotating the disks was (ab)used for this particular project.

A partial image of the visuals, owing to camera exposure time


Never tiring, a Brush Less Direct Current Motor, or BLDC for short, ball-born and almost without sound spins those valuable disks, and with them, our data. Even without maintenance, they spin with anywhere near 10,000 RPM for years on end, until replaced by their user in his or her everlasting quest for more capacity. No man could say if the number of hard drives is counted in the millions or the billions. Without question, every household somehow involved with electronics will contain one or more specimen no longer in use. While they constantly seem to grow too small for our needs, actual mechanical failure is comparatively rare. So why not introduce those motors, brush-less though they may be, to a new purpose? Heave no more the heavy burden of all our daily data needs, come the era of joy and fascinating pendular motions! And may no man pose the question if there is any point to all this!

A small selection of motors commonly found in hard drives


Mounted upright and equipped with a pendulum-shaped weight on the axis, gravity will see to set the construct in motion upon deflection, if only for a short while. After only a couple swings, the energy is consumed and the pendulum comes to a rest. Luckily, our BLDC can also act as a generator. Moving against each other, inductors and magnets inside it emit a phase-delayed current. When tracing this current, the angle at which the motor started its ascent can be measured with some accuracy. Through continuous monitoring and by turning on the motor for an instant, the lost energy can be replaced and the motion continues. No sweat, all it takes are some circuits and a microcontroller to take care of that.

Three thin wires supplying electricity and data


While a near-floating pendulum is a nice thing to have, it's severely limited it its use. Due to a lack precision or control over rotation speed, metronome duty is out of question. Nothing quite like a single line of LEDs to help against that monotonous noise it produces, and here's our very own motion-driven display waiting to draw graphics or text (like the time) on the pendulum's arc. The moving unit contains a second SMD microcontroller to avoid too many wires leading to every single LED. The display graphics are compressed on a PC and transferred to the unit via USB.

RGB-LED line on the moving unit


USB and pendulum controls

Back view of moving unit




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