fourJS — the §119 flagship: an electric motor digital twin. A motorised shaft on two bearing hinges inside a stator that is itself sprung on a compliant mount, so rotor unbalance produces real vibration; a `PIDController` closing the speed loop; live torque, speed, vibration and temperature instruments in engineering units; fault injection; and §34 record / seek / replay with §79 save-and-reload.

starting…