Ask Hackaday: How Do You DIY a Top-Octave Generator?

One of the great joys of Hackaday are the truly oddball requests that we sometimes get over the tip line. Case in point: [DC Darsen] wrote in with a busted 1970s organ in need of a new top-octave generator, and wondered if we could help. He had found a complicated but promising circuit online, and was wondering if there was anything simpler. I replied “I should be able to get that done with a single Arduino” and proceeded to prove myself entirely wrong in short order.

So we’re passing the buck on to you, dear Hackaday reader. Can you help [DC Darsen] repair his organ with a minimum amount of expenditure and hassle? All we need to do is produce twelve, or maybe thirteen, differently pitched square waves simultaneously.

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Mechanisms: Mechanical Seals

On the face of it, keeping fluids contained seems like a simple job. Your fridge alone probably has a dozen or more trivial examples of liquids being successfully kept where they belong, whether it’s the plastic lid on last night’s leftovers or the top on the jug of milk. But deeper down in the bowels of the fridge, like inside the compressor or where the water line for the icemaker is attached, are more complex and interesting mechanisms for keeping fluids contained. That’s the job of seals, the next topic in our series on mechanisms.

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Mechanisms: The Screw Thread

They hold together everything from the most delicate watch to the largest bridge. The world is literally kept from coming apart by screws and bolts, and yet we don’t often give a thought to these mechanisms. Part of that is probably because we’ve gotten so good at making them that they’re seen as cheap commodities, but the physics and engineering behind the screw thread is interesting stuff.

We all likely remember an early science lesson wherein the basic building blocks of all mechanisms laid out. The simple machines are mechanisms that use an applied force to do work, such as the inclined plane, the lever, and the pulley. For instance, an inclined plane, in the form of a splitting wedge, directs the force of blows against its flat face into a chunk of wood, forcing the wood apart.

Screw threads are another simple machine, and can be thought of as a long, gently sloped inclined plane wrapped around a cylinder. Cut a long right triangle out of paper, wrap it around a pencil starting at the big end, and the hypotenuse forms a helical ramp that looks just like a thread. Of course, for a screw thread to do any work, it has to project out more than the thickness of a piece of paper, and the shape of the projection determines the mechanical properties of the screw.

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MIDISWAY Promises to Step Up Your Live Show

If you like to read with gentle music playing, do yourself a favor and start the video while you’re reading about [Hugo Swift]’s MIDISWAY. The song is Promises, also by [SWIFT], which has piano phrases modulated during the actual playing, not in post-production.

The MIDISWAY is a stage-worthy looking box to sit atop your keys and pulse a happy little LED. The pulsing corresponds to the amount of pitch bending being sent to your instrument over a MIDI DIN connector. This modulation is generated by an Arduino and meant to recreate the effect of analog recording devices like an off-center vinyl or a tape that wasn’t tracking perfectly.

While recording fidelity keeps inching closer to perfect recreation, it takes an engineer like [Hugo Swift] to decide that a step backward is worth a few days of hacking. Now that you know what the MIDISWAY is supposed to do, listen closely at 2:24 in the video when the piano starts. The effect is subtle but hard to miss when you know what to listen for.

MIDI projects abound at Hackaday like this MIDI → USB converter for getting MIDI out of your keyboard once you’ve modulated it with a MIDISWAY. Maybe you are more interested in a MIDI fighter for controlling your DAW. MIDI is a robust and time-tested protocol which started in the early 1980s and will be around for many more years.

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UAV Coaxial Copter Uses Unique Drive Mechanism

Personal UAV’s are becoming ubiquitous these days, but there is still much room for improvement. Researchers at [Modlab] understand this, and they’ve come up with a very unique method of controlling pitch, yaw, and roll for a coaxial ‘copter using only the two drive motors.

In order to control all of these variables with only two motors, you generally need a mechanism that adjusts the pitch of the propeller blades. Usually this is done by mounting a couple of tiny servos to the ‘copter. The servos are hooked up to the propellers with mechanical linkages so the pitch of the propellers can be adjusted on the fly. This works fine but it’s costly, complicated, and adds weight to the vehicle.

[Modlab’s] system does away with the linkages and extra servos. They are able to control the pitch of their propellers using just the two drive motors. The propellers are connected to the motors using a custom 3D printed rotor hub. This hub is specifically designed to couple blade lead-and-lag oscillations to a change in blade pitch. Rather than drive the motors with a constant amount of torque, [Modlab] adds a sinusoidal component in phase with the current speed of the motor. This allows the system to adjust the pitch of the blades multiple times per rotation, even at these high speeds.

Be sure to watch the demonstration video below. Continue reading “UAV Coaxial Copter Uses Unique Drive Mechanism”