With just a few external components (Hall-sensor and a small magnet) you can enable this feature
preventing the risk of damaging your propeller during landing or (Scale Sailplane) motor pod
propeller retraction.
The magnet needs to be properly fixed to the rotating part (either motor or the propeller), and the Hall-sensor
has to be located in the fuselage, so that the magnet matches the Hall-sensor at the target propeller position.