It used a cam on the propeller shaft to push on a rod which pushed the ... bullet either sooner or later enough to hit a propeller blade. Propeller speeds also varied during the flight.

After acquiring an inflatable stand-up paddleboard and trying it out a few times, [Bitluni] decided to skip the “stand up” and “paddle ... out the prop to fit the shaft, he realized ...

which means instead of leaving the blade tips free as regular propellers do, the Sharrow CX connects its six blades—which are grouped in two triads—back to the propeller shaft in a smooth ...