Part One

Although my fitness related interest at the time didn’t involve martial arts — it quickly became apparent that would be a good use case for the initial prototype. The idea came to me as I was testing the prototype and found I had to make extreme motions in order to measure the effects of speed and rotation. That turned out to be an issue in the programming regarding sensor sensitivity. While testing, the motions reminded me of wielding a sword — which lead to a project code name: eKatana or electronic katana.

I studied martial arts for much of my youth — mostly as a side interest — so I guess that the measurement of angular momentum wasn’t a new concept, although that wasn’t how we referred to it in the Dojo. A quick search on YouTube for the term katana sword exhibition will give you a sense of the extreme dedication, precision and overall mastery involved. To say it’s awe-inspiring would be an understatement.

Rodrigja via wikimedia

But, alas I digress. What if one could take a practice sword and retrofit it with sensors to track the quality of motion? And what if one could build a mobile application to analyze that data in realtime? Would that be useful? While we’re seeing rapid advancements in AI — a Siri-like trainer is still some time away. And we’re even further away from replacing a human Sensei. Singularity notwithstanding. That’s just my bet. However, since science fiction has a way of becoming science fact, it isn’t difficult for one to imagine a Jedi knight training sword, complete with holographic Sensei.

So adding tracking capabilities to a sword allows it to become a smart device. Which presumably has fitness and training implications. That offers us our first “why”. And perhaps for someone — successful execution of such a product could lead to potential financial rewards, which offers us a second “why”. But it’s the third “why” that’s most important to me… hacking is about exploring — often without monetary motives and for many of us, that’s often enough of a “why”.

Let’s have a closer look at the tech behind such a smart device before getting into the “how” that makes it possible. Referring back to my twitter post in January, we see a prototype of a Bluetooth enabled device which is capable of tracking motion. It’s also powered by a tiny battery making it highly portable. Think of that device as the brains of our sword.

Naturally, we still need an actual sword. It didn’t take long to track down a $16 polypropylene training sword on Amazon— it’s the one shown in the next series of photos.

After numerous layout considerations, I managed to get the device down to one inch by two inches, with a height of just over a quarter inch. Further size reductions are certainly possible. I suspect that a near 50% reduction in size and lower costs at scale — but those are re-engineering and mass production challenges.

Device fits perfectly on the Katana’s handle

Sadly, the practice sword I purchased does not have a hollow base, so the module can’t easily fit inside the handle. But clearly, it’s small enough to do so. Potential solutions include 3D printing an extended base. That said, I suspect that an ideal location for the sensors would be at the tip of the blade — but that discussion is outside the scope of this post.

Device positioned with charging port facing out for easy charging

Once the Katana charges (in just under an hour) the practitioner would then pair it with a mobile phone or tablet. A mobile app receive the emitted Bluetooth data. A full-featured app could provide practice motions and measure force and accuracy. Data could then be sent to a cloud-hosted service for longer term storage and or deeper analysis.

In the next part, we’ll have an in-depth look at the tech.