The inner workings of servo motors

Servos seem to be the go-to option when adding motors to hobby projects. They’re easy to hack for continuous rotation for use in a robot, but with the control board intact they are fairly accurate for position-based applications. But do you know how the hardware actually works? [Rue Mohr] recently published an article that looks at the inner world of the servo motor.

As you know, these motors use a voltage, ground, and signal connection for control. The position of the horn (the wheel seen on the servos above) is dependent on that control signal. The duty cycle of a 20 ms pulse decides this. Inside the housing is a control board capable of measuring this signal. It’s got a chip that monitors the incoming PWM pulses, but that’s only half of the equation. That controller also needs feedback from the horn to know if its position is correct or needs to be changed. Integrated with the gear box that connects the motor to the horn is a potentiometer. It’s resistance changes as the horn turns. Knowing this, it is possible to fine tune a servo by altering that resistance measurement.

27 MHz transmitter/receiver pair made with 555 timers

Get your feet wet with radio frequency transmitters and receivers by working your way through this pair of tutorials. [Chris] built the hardware around a couple of 555 timers so you don’t need to worry about any microcontroller programming. He started by building the transmitter and finished by constructing a receiver.

Apparently the 27 MHz band is okay to work with in most countries as long as your hardware stays below a certain power threshold. The carrier frequency is generated by the transmitter with the help of a 27.145 MHz crystal. The signal is picked up by the receiver which uses a hand-wrapped inductor made using an AL=25 Toroid Core. We’d say these are the parts that will be the hardest to find without putting in an order from a distributor. But the rest of the build just uses a couple 555 timer chips and passive components, all of which will be easy to find. The video after the break shows the project used to receive a Morse-code-style message entered with a push button. It would be fun to interface this with your microcontroller of choice and implement your own one-way error correction scheme.

Open source finger prosthesis

Here’s a project that is striving to develop a set of open source finger prosthesis. They are aimed at patients who have partial amputations. This means that part of the digit remains and can be used as the motive force behind a well designed mechanical prosthesis like you see above. This uses levers, pulleys, and wire to move a gripper in much the same way the pad of a pointer finger works. There’s even a video (embedded after the jump) which shows it being used to grab a toothpick from a dispenser… pretty impressive. This is similar to the prosthesis we saw in August which managed to work without pulleys and wire.

This isn’t limited to fingers. The same posts that shows off the unit seen above also includes a prosthetic thumb. The leverage for that design is provided by a woven nylon strap which attaches to a bracelet on the wrist.

[Read more...]

Hackaday Links: October 18, 2012

Capacitive touch plants

Here’s a proof of concept for using plants as a capacitive touch sensor. The sensor is simply a hunk of double-sided copper clad board attached to a microcontroller. But it seems to be able to sense what part of the plant is being touched. [Thanks Fabien]

Adding wireless charging to a Nokia N900

This hack is quite common, but it’s still fun to see what hardware is being outfitted with an inductive charger. This time it’s a Nokia N900 that’s ditching the charging cables.

Wii carrying suitcase from a plastic tackle box

This Wii carrying case (translated) looks great and cost just a few bucks. It started as a tackle box for carrying around your fishing lures. But a bit of creative cutting and there’s a place for everything.

Browser based schematic and board layout

There’s a new kid on the block when it comes to circuit design. offers in-brower schematic design and board artwork layout. [Thanks ADIDAIllinie (and a few others)]


Halloween rapidly approaches and we hope that [Tim's] carving of Bender in a pumpkin will inspire you to send in your own Halloween projects.

Unlocking silk for uses as an optical, digital, biological, or food storage device

[Fiorenzo Omenetto] gave a TED talk early last year to illustrates a lot of intriguing uses for silk. Before watching his presentation we would have been hard pressed to come up with a use for silk other than in clothing. But it turns out that investigating how silk worms create the material has led to a range of other applications. You can see the full talk embedded after the break.

One of the first things he shows off is a transparent film made of silk. The material looks almost like cellulose film, and can function in a similar way. [Fiorenzo] shines a laser through a silk slide that has a micro-dot of words embedded in it. the result is a clearly readable message projected on the wall. The film can also be used for holographic images.

But it’s the biodegradable aspects that are clearly the breakthrough here. A slide of silk can be doped with pharmaceuticals and programmed for a very specific time release. This way the drugs no longer need to be stored under refrigeration, and can be reclaimed using only water. The same properties allow one to manufacture disposable objects that will quickly and completely degrade. But there’s even more, if you dope the material with a conductor like gold it becomes a disposable circuit.

[Read more...]

Most useless machine: building elevator edition

[Niklas Roy] calls it his Perpetual Energy Wasting Machine, but we know it for what it truly is: a building-sized most useless machine. You’ll remember that a most useless machine is a bobble that uses clever design to turn itself off once you have turned it on. This does the same thing with the elevator of the WRO Art Center in Wroclaw, Poland. The one difference is that it continually turns itself on and off.

He rigged up a pulley system that travels through the stairwell of the building. Whenever the elevator door on the top floor opens it causes the call button on the bottom floor to be pressed. The same thing happens when the elevator reaches the ground floor. But he didn’t stop there. Since the device is just wasting electricity whenever the elevator moves without passengers in it, he added a meter to track the loss. It’s the guts of a printing calculator strapped to the inside of the car. Every time the doors open it adds to the total.

You can see the installation in the video clip after the jump.

[Read more...]

Creating a MIDI synth from a Commodore SID

The Commodore SID was the audio chip in the venerable Commodore 64 and in the 30 years since release has attained classic status and become one of the best ways to get your chiptune on. Designed by famous synthesizer designer [Bob Yannes], it was only a matter of time before we saw a real, homebrew MIDI synth based on the Commodore SID.

Because real SID chips are rare as hen’s teeth nowadays, [Jeff Ledger] built his SID synth around an emulated system running on a Pocket Mini Computer. This very cool microcontroller platform runs on the Parallax Propeller. An emulated SID runs in one of the Propeller’s 8 cores, with the remaining cores kept open for reading MIDI notes and displaying info on a display.

The hardware portion of this build is amazingly simple; just an optoisolater, a few resistors, and a diode connect a MIDI keyboard to the Pocket Mini Computer. The buttons and dials on [Jeff]‘s MIDI keyboard control the waveforms, filters, and envelope controls. A very neat setup if we do say so ourselves, and just perfect if you’re needing more chiptunes in your life.

You can check out [Jeff]‘s video after the break.

[Read more...]