When I decided to start making my own frames, the Flapjack was one of the first projects I did. Being a small frame, it meant wasting less material if I got things wrong when getting to grips with the CNC machine, and it was a fun little challenge incorporating CNC routed carbon, HDPE, and 3D printing too.
Originally it was designed as a sort of easier to build, more versatile version of a Blade Torrent style quad, with solid propguards that could take a bit of abuse. The HDPE proved excellent for that - initial design included a brace across the centre, but that was omitted for later versions as it didn't increase strength by any measurable amount, and hugely increased manufacturing time due to needing the whole circular guard be pocketed out and reduced to dust rather than just cutting the inside profile to leave a large solid cylinder of waste.
Once the frame was made, it proved to be a nice quad to fly except for one odd characteristic - in high speed forward flight, when descending into a turn it had a nasty habit of snap rolling to the inside (so on a left turn it would roll hard left). I established this was aerodynamic in nature - the propguards work excellently at low speed, but at high speed they can create a "shadow" and block air from reaching the propellers, leading to unpredictable behaviour. On the bright side, this led to extensive crash testing which proved the strength of the frame as a whole.
Regardless of its flaws, the Flapjack proved to be a successful first project - however, by the time it was complete, smaller quads like the original Tiny Whoop had become prevalent and the idea of a 100mm+ quad seemed dated, so I didn't take it any further. More than a year later, however, I came back to the project once the Cinewhoop movement gained momentum, and it evolved into a tiny GoPro hauler for proximity shots in tough conditions - the Hoverfly.