This year for the Kentucky Derby horse race, NBC asked my team at Viget to refresh a project we debuted during the 2016 race: a Particle-powered brooch to encourage viewers at home to participate in the race-day festivities. Whenever a viewer tweets the hashtag #WatchMeNeighNeigh, the animatronic horse and LEDs on our bedazzled brooch leap to a gallop.
The team and I enjoyed building the brooch for NBC, and we wanted to share a few tips and tricks so you can try creating your own version. Keep reading to learn about the electrical, mechanical, and aesthetic considerations that go into building a wearable powered by Particle!
Step 1: Custom PCB for custom fit
We knew we needed a slick design to house everything inside a small brooch. Previous iterations of the project used a large hip-mounted battery pack. Inside the cavernous enclosure was either a Particle Photon or Electron alongside a huge LiPo. It was a good first step and enabled the wearer to wander around the venue without losing connectivity. However, its size made it clunky, and it required a 5-conductor wiring harness which was extremely difficult to connect discreetly through a jacket.
The most recent iteration of the brooch was designed around a donut-shaped printed circuit board (PCB). Why a donut? Well, as you can see above, the servo needed to squeeze in somewhere!
In this iteration, we also decided to put the brain inside the brooch itself. The result was a simple 2-layer board affording just enough space for the Particle P1, an I2C bus, an accelerometer, servo control, and 28 addressable RGB LEDs. Here are our Gerber design files to get you started.
Power is provided to the device through two brass pins soldered directly to the PCB. We used these same pins to secure the brooch to the garment. This allowed our celebrity brooch-wearer to pocket a small USB battery bank and discretely power the brooch from inside a shirt or jacket.
Note: sourcing addressable LEDs can be difficult in the US. We were on a time crunch, so we asked Macrofab (a PCBA house in Houston, TX) to tackle one side of the PCB while we sourced LEDs and eventually reworked the other side in-house.
Step 2: Miniature animatronic horse
The team had never seen or worn an animatronic brooch. It wasn’t a Google-able concept. But we wanted to produce a fully articulating horse, and it needed to be simple to build and repair.
After some experimentation, we settled on a solution where every component was 3D printed (feel free to use our STLs to get started). The only servo drove a printed linkage between the printed horse’s legs; this makes the horse gallop. The head and tail then rested on those legs to achieve a slight head bob and tail wag of sorts — it was simple, clean, and worked well.
We’re fans of the Lulzbot suite of 3D printers and found the .5mm nozzle perfectly adequate despite the miniature scale. Every component was produced from transparent NGEN (a copolymer) that was easy to machine and finish.
Most importantly, the horse was also dimensionally stable across all axes. If we needed the head to bob a bit more, or the tail to wag a hair less, we could make those discrete changes in Fusion 360 and rely on the Lulzbot to quickly produce the new component.
Finally, separate components were connected together with M2 brass inserts and screws. These can be purchased from McMaster Carr; however, we recommend Alibaba for bulk.
Step 3: Aesthetics matter
We need the brooch to look terrific, so we thought through the details and broke open the jar of glitter. In collaboration with the client, we settled on a bedazzled horse with a shimmering gold backdrop that would match the wearer’s outfit. Though it’s not apparent (some good tricks go unseen) we modeled definition onto the 3D printed components of the horse. This lets the gems follow a 3D geometry which helped the brooch create depth on camera.
Another trick we came across was using spray primer as both a paint base and a diffusion layer treatment. Because the overall brooch was thin, and the LEDs were squished right against the translucent NGEN backdrop of the horse, we needed a mechanism for scattering emitted light as early as possible. Applying primer to the inside of any illuminated surface helped diffuse light and eliminate hotspots.
Overall, this was a fun project to be a part of. While it looked little on TV, it was full of big and interesting challenges. Good luck building your own tiny galloping horse, or whatever this might inspire for your next project!