Six foot speaker shakes buildings to their foundation

In the first scene of Back to the Future, [Marty McFly] visits the unoccupied laboratory of [Doc Brown]. Seeing an 8-foot-tall speaker connected to a huge array of amplifiers, [Marty] immediately turns on the amps, plugs in an electric guitar, and promptly destroys the amps and speaker while being thrown across the room. This scene must have been a huge inspiration to [Dan] and [Kyle]; they decided to replicate this gigantic speaker for the 2011 UW-Madison  Engineering Expo.

A speaker is a remarkably simple device – they’re usually just a coil of wire, a set of magnets on an iron frame, and a cone. [Dan] and [Kyle] wound hundreds of feet of copper wire around a fiberglass frame for the voice coil, used 8 and 10-inch steel pipe to secure the magnets, and pop riveted two sheets of polycarbonate together to form the cone. The result is a six-foot-diameter speaker in an 8x8x2 foot enclosure.

A speaker this size is only good for one thing: a ton of bass. The speaker can reliably reproduce frequencies from 5 Hz to 50 Hz, frequencies that are better felt than heard. There’s a video of the speaker in action after the break, but we’re pretty sure the best way to experience this insane device is in person.

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Sensor rig finds out if motorists are sharing the road with cyclists

Apparently there’s some cause for concern when it comes to bikes and automobiles sharing the roads in Austin, Texas. [Christopher Stanton] wrote in to tell us there’s a law on the books now that requires motorists to give three feet of space when passing a cyclist. This is pretty difficult to enforce as there’s no solid proof like the radar gun provides when it comes to speed limits. The hardware above is seeking to help by collecting data on passing habits. It measures and records the distance of each vehicle that passes you while on the bike. The goal isn’t to ticket more drivers, it’s to collect statistical data that might help change dangerous driving habits.

As you can see, a front equipment rack hosts the hardware for easy installation on a bike. It has an arm that extends to the side the same distance as the handle bars. The HD camera with wide-angle lens is set to snap a photo which can be used to determine the bike and vehicle positions in the lanes, along with the distance readout from the sensor.

We’d certainly be interested in seeing the numbers for average passing clearance in a heavily traveled urban environment. Even with bike lanes, things can feel pretty tight on a busy day!

Foot-controlled mouse keeps your hands on the keyboard

A bit of mechanical ingenuity makes building this foot-controlled mouse into a fun project. It consists of a platform which hosts one pedal for each foot. The right foot controls the movement of the cursor, and the left is responsible for the buttons.

The guts of a wireless mouse do most of the electrical work for this hack. You can see that the optical sensor is mounted on the front of the right foot pedal. A ball bearing combined with a hinge provides motion on two axes. This moves the sensor past a piece of curved foam made by covering a ball with plastic wrap then spraying foam insulation around it. The pedal on the left has four buttons actuated by moving the toes down, up, left, or right. There’s a centering mechanism for this pedal which uses a rubber band

One thing we wonder about here is whether there is a need to lift and re-center the mouse/cursor? There is also no scroll wheel. But those issues are just waiting for someone to pick up the project and make their own improvements.

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