Ask Hackaday: What Are Magnetic Gears (Good For)?

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.

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Hackaday Prize Entry: What The Flux

Electromagnetism is the most difficult thing teach. Why is electromagnetism hard to teach? Well, when you’re asking a ‘why’ question (obligatory Richard Feynman video)

[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.

Hackaday Prize Entry: Measuring 3D Magnetic Fields

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.

Magnetized screwdriver in the "valley"
Magnetized screwdriver in the “valley”

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 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.

Hackaday Prize Entry: Visualizing Magnetic Fields

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.

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3D Carver Makes Magnetic Fields Visible

The history of science is full of examples when a 3D physical model led to a big discovery. But modelling something that’s actually invisible can be tough. Take magnetic fields – iron filings on a card will give you a 2D model, but a 3D visualization of the field would be much more revealing. For that job, this magnetic field following 3D carving machine is just the thing.

What started out as a rapid prototyping session with servos and hot glue ended up as quick and dirty 3D carving rig for [Frits Lyneborg]. The video shows his thought progression and details how he went from hot glue and sticks to LEGO Technics parts and eventually onto Makerbeam extrusions for the frame of his carver. A probe with a Hall effect sensor is coupled to a motor spinning a bit that cuts into a block of floral foam. A microcontroller keeps the Hall sensor a more or less fixed distance from a rare-earth magnet, resulting in a 3D model of the magnetic field in the foam, as well as a mess of foam nubbles. Despite a few artifacts due to in-flight adjustments of the rig, the field presents clearly in the block as two large lobes.

Carving foam isn’t the only way to visualize a magnetic field in three dimensions, of course. If you’d rather have a light show based on the local magnetic field, try this 3D compass build we covered a while back.

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Levitating Objects In Paramagnetic Liquids

Two weekends ago was the Bay Area Maker Faire, and lacking a venue to talk to people who actually make things, we had a meetup at a pub. This brought out a ton of interesting people, and tons of interesting demos of what these people were building. By either proclivity or necessity, most of these demos were very blinkey. The demo [Grant McGregor] from Monterey Community College brought was not blinkey, but it was exceptionally cool. He’s levitating objects in paramagnetic liquids with permanent magnets.

Levitating objects in a paramagnetic solution around a magnetic field has been an intense area of research for the Whitesides Research Group for a few years now, with papers that demonstrate methods of measuring the density of objects in a paramagnetic solution and fixing diamagnetic objects inside a magnetic field. [Grant] is replicating this research with things that can be brought to a bar in a small metal box – vials of manganese chlorate with bits of plastic and very strong neodymium magnets. The bits of plastic in these vials usually float or sink, depending on exactly what plastic they’re made of. When the paramagnetic solution is exposed to a magnetic field, the density of the solution changes, making the bits of plastic sink or float.

It’s a bizarre effect, but [Grant] mentioned a nurd rage video that shows the effect very clearly. [Grant]’s further experiments will be to replicate the Whitesides Research Group’s experiment to fix a diamagnetic object inside a magnetic field. As for any practical uses for this effect, you might be able to differentiate between different types of plastic (think 3D printing filament) with just a vial of solution and a strong magnet.

[Grant] was heading out of the pub right when I ran into him, but he did stick around long enough to run into the alley behind the pub and record an interview/demo. You can check that out below.

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A DIY Geomagnetic Observatory

Magnetometer observatory

[Dr. Fortin] teaches physics at a French High School, and to get his students interested in the natural world around them, he built a geomagnetic observatory, able to tell his students if they have a chance at seeing an aurora, or if a large truck just drove by.

We’ve seen this sort of device before, and the basic construction is extremely similar – a laser shines on a mirror attached to magnets. When a change occurs in the local magnetic field, the mirror rotates slightly and the laser beam is deflected. Older versions have used photoresistors, but [the doctor] is shining his laser on a piece of paper and logging everything with a webcam and a bit of OpenCV.

The design is a huge improvement over earlier DIY attempts at measuring the local magnetic field, if only because the baseline between the webcam and mirror are so long. When set up in his house, the magnetometer can detect cars parked in front of his building, but the data he’s collecting (French, but it’s just a bunch of graphs) is comparable to the official Russian magnetic field data.