rubic: a live F2L trainer for a smart cube

Smart-cube apps tell you your time. That was never my problem: I lose track of pieces, I'm slow to spot which pair goes next, and I rotate the whole cube far more than I should. A stopwatch shows none of that.

What I wanted was each of the four first-layer pairs split in two — seconds spent staring, seconds spent turning. Whichever pair the staring dominates is the one to drill. So the trainer's main output is that table: cross plus four pairs, pause time and turning time in their own columns.

It's two single-file pages served locally. One is a reference — every CFOP case as a 3D cube you step through move by move, from the 8 cross cases to the 21 PLLs. The other talks to a Bluetooth cube that reports each turn as it happens, and walks me through the next pair.

The hard part was never solving the cube. Three sets of directions disagree — what the firmware reports, what the 3D engine uses, and what I see holding the cube my way are a whole-cube flip apart. Get one wrong and the screen demonstrates the bottom layer while you turn the top. It only settled once all three went through one shared mapping table.

The solver was the other rewrite. Searching for the shortest path matched what I was actually memorising in 4 of 41 cases — short, but no use for practice. The tables are now generated offline, and every lookup is replayed against a simulated cube before it reaches the screen: does it place the pair without wrecking the cross or a slot already finished? That check earns its keep — about a third of the supplementary entries broke a finished slot.

A self-check script runs with no hardware attached: syntax, the 18 direction mappings, table sizes, and whether any algorithm sneaks in a move the cube cannot report. It passes. On 4 July I recorded one complete solve on the real cube — 155 seconds, 54 moves, 24% of it paused. August brought a large rewrite, and Bluetooth, gyroscope and colour resync can only be confirmed against the physical cube. My own notes say so.

It isn't only for me any more — the plan is to turn it into a course and sell it.