A drift is an angle held on purpose. This measures the angle.
YAW estimates a drift car's slip angle — the angle between where it points and where it travels — from the sensors already in a phone, and turns each run into something you can read.
Drift practice is hard to improve at because it is hard to see. A run feels good or bad, and the feeling is the only record. Measure the angle, corner by corner, and the reps start to compound: which corner is inconsistent, which one is already solved, what to work on next time.
It runs on the phone, installs to the home screen and works with no signal at the track. A Raspberry Pi is an optional upgrade, not a requirement — a fused motion sensor, a 10 Hz GNSS receiver, and a tap into the car's own ECU over CAN.
It sits inside a larger coaching system — technique, track knowledge, competitor intel and event history, structured so the advice is about this car and these tracks rather than about drifting in general. The telemetry feeds it; the coaching reads it back.
The data schema is not YAW's alone. driftclip's telemetry overlay draws the same channels, so one definition serves both the instrument in the car and the clips cut from the sim. A second definition would be a bug.
Four channels, and what each one is for.
Slip angle
The core number. How far sideways the car is actually travelling, held against where it is pointed.
The line
Where the car went, sharp enough to split a lap into corners and compare one against another.
Grip
Lateral and longitudinal g as a traction circle — how much of the tyre was being used, and where it ran out.
The engine
Throttle, RPM, boost and gear, taken off the car's own CAN bus rather than inferred.
The app is live and in use. The hardware is built and has not been in the car.
Built and running: the live heads-up display, hands-free recording, per-corner breakdowns, lap-against-lap comparison, session trends, a coaching pass that turns all of it into one ranked focus, and a tandem mode that reads two cars against each other. The v1 sensor kit is assembled and the bring-up is scripted end to end.
What is left is physical. The unit has to be mounted in the car, wired to the ECU, and taken out for a session that comes back with numbers worth trusting. Everything after that — the second unit, and tandem in real competition — waits on that one afternoon.