If you’ve ever had a particularly nasty fracture, your doctor may have prescribed the use of an electronic bone growth stimulator. These wearable devices produce a pulsed electromagnetic field (PEMF) around the bone, which has been shown to speed up the natural healing process in a statistically significant number of patients. That’s not to say there isn’t a debate about how effective they actually are, but studies haven’t shown any downsides to the therapy, so it’s worth trying at least.
When you receive one of these devices, it will be programmed to only operate for a certain amount of time or number of sessions. Once you’ve “used up” the bone stimulator, it’s functionally worthless. As you might imagine, there’s no technical reason this has to be the case. The cynic would say the only reason these devices have an expiration date on them is because the manufacturer wants to keep them from hitting the second hand market, but such a debate is perhaps outside the scope of these pages.
The Orthofix SpinalStim you’re seeing here was given to me by a friend after their doctor said the therapy could be cut short. This provided a somewhat rare opportunity to observe the device before it deactivated itself, which I’d hoped would let me take a closer look at how it actually operated.
As you’ll soon see, things unfortunately didn’t work out that way. But that doesn’t mean the effort was fruitless, and there may yet be hope for hacking these devices should anyone feel like taking up the challenge.
Just when you though it was safe to venture out, the National Oceanic and Atmospheric Administration released an unexpected update. Magnetic North is on the move — faster than expected. That’s right, we know magnetic north moves around, but now it’s happened at a surprising rate. Instead of waiting for the normal five year interval before an update on its position, NOAA have given us a fresh one a bit earlier.
There are some things that we can safely consider immutable, reliable, they’ll always be the same. You might think that direction would be one of them. North, south, east, and west, the points of the compass. But while the True North of the Earth’s rotation has remained unchanged, the same can not be said of our customary method of measuring direction.
Earth’s magnetic field is generated by a 2,000 km thick outer core of liquid iron and nickel that surrounds the planet’s solid inner core. The axis of the earth’s internal magnet shifts around the rotational axis at the whim of the currents within that liquid interior, and with it changes the readings returned by magnetic compasses worldwide.
The question that emerged at Hackaday as we digested news of the early update was this: as navigation moves inexorably towards the use of GPS and other systems that do not depend upon the Earth’s magnetic field, where is this still relevant beyond the realm of science?
How could you build an artificial tadpole? Or simulate the motion of a cilium? Those would be hard to do with mechanical means — even micromechanical because of their fluid motion. Researchers have been studying shape-programmable matter: materials that can change shape based on something like heat or magnetic field. However, most research in this area has relied on human intuition and trial and error to get the programmed shape correct. They also are frequently not very fast to change shape.
[Metin Sitti] and researchers at several institutions have found a way to make rapidly changing silicone rubber parts (PDF link) that can change shape due to a magnetic field. The method is reproducible and doesn’t seem out of reach for a hackerspace or well-equipped garage lab.
Magnetic gears are surprisingly unknown and used only in a few niche applications. Yet, their popularity is on the rise, and they are one of the slickest solutions for transmitting mechanical energy, converting rotational torque and RPM. Sooner or later, you’re bound to stumble upon them somewhere, so let’s check them out to see what they are and what they are good for.
[Adam Smallcomb] might not be able to explain electromagnetism with perfect clarity, but he does have an idea to give students a hands-on feel for electrons and magnets. He’s building an Electromagnetic Teaching Aid that turns 30 gauge wire, springs, Lego, and bits of metal into a toolset for understanding magnets, solenoids, current, and magnetic fields.
The devices explained via [Adam]’s toolkit include a DC motor, stepper motor, speaker, solenoid, relay, transformer, microphone, and generator. That’s not to say [Adam] is building all these devices – a DC motor is just a generator in reverse, a relay is a solenoid with more electrical connections, and everything in this toolkit is basically just wire and magnets.
So far, [Adam] has a bunch of interesting applications for magnets, wire, and Lego including a DIY stepper motor and a nifty little tool that measures magnetic flux with a Hall effect sensor. Will it teach schoolkids electromagnetism? Very few things could, but at least this little toolkit will allow students to intuit electromagnetism a little better.
Sometimes you have to start out with big goals. Ninth-graders [Finja Schneider] and [Myrijam Stoetzer] are aiming to make a magnetic field scanner that would be helpful in finding large underground metallic objects, like unexploded WWII bombs that pose a real threat whenever a new parking garage is excavated in Germany. But even big goals have to start out somewhere, so they’re gaining experience with the sensors and the math necessary to recreate 3D magnetic flux vector fields on household objects like sawblades and magnetized screwdrivers.
For their science-fair project, [Finja] and [Myrijam] took a mid-80s fischertechnik “toy” 2D scanner kit, mounted a 3D magnetic sensor to it, and wrote some firmware to scan around and pass the data back to a computer where they reconstructed the field lines and made some nice visualizations. Along the way, they tried a number of designs, from a DIY chassis on carbon-fiber rails to sensors with ferrofluid. They document their successes and failures equally nicely in their lab report (PDF, German). You can get a lot of the gist, however, from [Myrijam]’s blog and their Hackaday.io entry.
You might also recognize [Myrijam] from her work with [Paul Foltin] on their eye-controlled wheelchair interface. These are some really cool projects! We’re excited to see how they develop, and are stoked that the future of hacking is in such capable hands.
In 1820, Hans Christian Oersted discovered the needle of a compass would deflect when placed next to a wire carrying an electric current. It took 15 years for the first electric motor to be invented following this observation. Humans are dumb, but perhaps they wouldn’t be so oblivious to the basic facts of our reality if they could see magnetic fields. Or if they just had a 3D printer. For his Hackaday Prize entry, [Ted Yapo] is doing just this: adding a magnetic field scanner to a 3D printer, allowing for the visualization of magnetic fields in three dimensions.
The device [Ted] is working on is actually extremely simple, and is mostly implemented in software. The hardware is just a 3D printer with a toolhead consisting of a HMC5883L magnetometer breakout board. This is the simplest and easiest way to find the direction and intensity of a magnetic field, the rest of the work is done in software.
Right now, [Ted] has a setup that will scan a 3D volume with a printer. By placing a magnet in the middle of the print bed, he can visualize the magnetic field inside the volume of his 3D printer. It’s a visualization that is vastly superior to a compass, ferrofluid, or even a mess of iron filings, and is surely a much better pedagogical apparatus for classrooms and science museums alike.