SHDB16 – Building a Powerwalker

As it so happens another year passed in the blink of an eye. I moved places, made a house worth living in and got married. And last weekend it was already time for the Science Hack Day Berlin again, which attended last year with great success. I met great people and together we worked on my idea of a physical public transport times interface. Without my group it wouldn’t have turned out half as great as it did eventually. Good times.

So once the organizing team for the Science Hack Day Berlin 2016, who welcomed my former co-hacker Michaela as a recent addition to their team, opened registration for this year’s event, I not only did not hesitate to sign up but also talked Doro into joining me, she as a designer, me as a researcher/scientist.

Building up to the SHD we discussed potential projects over a couple of dinners. We wanted something cool, easy, related to design and novel(ish). We scrapped the idea of a photospectrometer for being too hard and not very interesting to Doro from a designer perspective (and it turned out that another group did a great job to join forces to elaborate on their idea of a photospectrometer) and we eventually settled on an electric generator.

We wanted to use the excess energy of a runner or walker and turn it into electrical energy to use for lights or maybe even, down the road, to charge a battery. This isn’t new, many have tried to get somewhere with this. Many designs however include system in the soles of the shoes or large backpack or brace-like devices that impede agility of the wearer. The shoe solution is also not easily applicable, technically challenging and not compatible with running shoes that are little wonders of technology on their own.

Our idea was to build a linear alternator, essentially a magnet jumping up and down between a copper coil. The change in the magnetic field in the coil induces a current that can be used in a LED, for example. The basic design and idea is simple, really, however the exact dimensions and many details of the body design were what we wanted to explore. Whether or not it’s even possible to get enough power for a LED was still unbeknownst to us.

So, on Friday night I pitched my idea amongst 14 others. Project ideas ranged from a cooking robot over sci-fi nail polish to a passive radar detector. We then formed groups and started talking and exploring ideas. Soon it was late and we headed home to gather supplies and regroup Saturday morning.

Some of the concepts we envisioned in our first get-together.

We ended up being three people in our little group, Marja, Doro and I, and we began by figuring out how to actually build our little generator. We collected our parts list and headed for shopping. Here is what we used for the project:

  • Enameled copper wire, 0.1 mm, roughly 400 m
  • magnets. We bought different sizes, the stronger, the better
  • A tube that has an inner diameter a bit wider than the magnets diameter
  • LEDs, resistors, diodes, wires, soldering equipment, shrink tubing…

Taking part in a science hack day, we did some science. Using the great app Science Journal from google we measured the vertical acceleration when running with the phone mounted on different positions on the body. Looking at the data we figured that either the ankle or the upper arm are the best positions to use the shock energy from each step.

Just before we headed off for Conrad  we welcomed a fourth member to our group. After shopping for parts we started the assembly of our generator. While the big magnets were quickly snatched together with some leftover electrical installation tubes by our new group member so he could build the prototype on his own, we were left with some smaller magnets. We build a first tube out of stably rolled up paper that we fixed on a battery powered drill and used that to wind our coil. The first one we built was rather wide, stretching out approximately over 60 % of the tube length. The magnet could just leave the coil on each end. We hooked the coil to a LED, with no resistor, and started shaking. Surprisingly, already that beginner’s coil was enough to light up the LED. With a flash every time the magnet passed the coil we could see that the principle worked well. However, we still needed a rather big shake to get the magnet moving, far too big to be practical when running.


The next iteration was greatly improved by two things. A friendly neighbourhood hacker gave us some acrylic tubes that fit perfectly to some new, round magnets we brought from home the next day. We wound a new coil, much tighter this time, around the acrylic tube. We cut the tube to length to house the magnets just outside the coil and closed it with two wooden caps. We hooked up the coil to two LEDs in parallel and again, enjoyed the light flashed every time the magnets bounced through the coil. Meanwhile, our fourth member had built his prototype, with a huge coil, two big magnets and a rubber mechanism to keep the magnets suspended in the coil. The result was a device that with already small movements could fire up a couple of LEDs to the point of almost burning through them.



So depending on what you want, a small magnet can be enough for a flashing LED, however to get a lot of power, use the biggest magnet with the biggest coil possible. The coil should be wound tightly, as narrow as possible to shorten the necessary path of the magnet. Suspending the magnet on rubber strings or letting it bounce off of springs on each end helps with using the most of each impulse when running.

Doro did a great job to film a lot on her phone, so I could put together a short video of the build process.

I guess I will continue to work on this and get a proper instruction together to build another Power Walker that is fully functional and can be actually used now in the dark season coming up. Thanks so much to Doro and Marja to work with me on this project!

Although we had some social interaction hick-ups within our group, both Doro and I were really happy to take part in this Science Hack Day 2016. We met a lot of lovely people and the organizers did a wonderful job of providing us with material, knowledge, Mate, pizza, conversations and prizes. Please feel invited to come to the next Science Hack Day in 2017!

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