The wheel is printed in PLA and holds 12 magents to supply the signal for a tachometer application. A Hall Effect sensor picks up the magnet field as the magnets pass by and produces a pulse for each one. The pulses are counted by a Raspberry Pi and RPM is calculated. The machine it is mounted on is a small DIY dynomometer being used to study DC motors for electric vehicles. The round silver motor in the picture is capable of producing over 13 HP despite its small size. The Hall Effect sensor is able to sense the magnets passing by right through the aluminum bracket it is mounted to. The LED flashes as each magnet passes by.
The 3D printed Magnet Wheel
The Raspberry Pi