A maker attempts a crankless bicycle that converts back-and-forth pedaling into steadier propulsion using gears, freewheels, and 3D-printed parts.
Pedaling has looked the same for more than a century, but one engineering build is trying to break the spell.
The modern bicycle’s core formula is instantly recognizable even across long timelines: a frame built around two triangles. wheels of equal size. and propulsion via pedal crank motion transferred through a chain in most conventional designs.. Improvements over time have mostly come from better materials and performance tuning. not from changing the fundamental way power is generated and transmitted.
That continuity is exactly why the “crankless” approach stands out.. Instead of relying on a crank’s circular motion. the concept swaps that rotational input for a more linear motion. aiming to produce propulsion that feels more consistent rather than cycling through the ups and downs of a crank-based stroke.
The inspiration for this build traces to an earlier mechanism that used a sinusoidal track inside a rotating cylinder to handle the conversion from one type of movement into another.. Here. the creator takes a different route: rather than converting motion through that specific geometry. the system uses an arrangement of gears and freewheels that acts like a mechanical rectifier.
In practical terms, the goal is to take the back-and-forth movement of pedaling and transform it into rotation. That rotation then becomes the bike’s drive motion, effectively reinterpreting what “pedaling” should mean while still landing at a familiar outcome: wheels turning under power.
The pedals themselves are also reimagined. Instead of standard pedal arms and cranks, the build uses stirrups mounted at each end of a V-belt arrangement, turning the rider’s leg motion into the linear back-and-forth movement the rest of the drivetrain is designed to rectify.
Where this project becomes especially demanding is in the hardware.. The build is presented as a stress test of what 3D-printed strength can handle. particularly in a geartrain that has to transmit force repeatedly under load.. Prototype after prototype shears during use. highlighting how quickly ideal designs can fail when materials and print characteristics meet real torque and impact.
After enough iterations, the creator does get the crankless bicycle working.. Even then. the broader message is less about a finished product and more about persistence against the practical limits of manufacturing. especially in moving drivetrain components that are typically engineered with far more conventional fabrication methods.
Notably, this is not portrayed as the first time someone has attempted a 3D-printed bicycle geartrain.. The effort sits within a small but growing tradition of builders experimenting with printed mechanical systems. where trial-and-error is often the price of pushing beyond what off-the-shelf parts can deliver.
For cyclists. the idea of a more constant propulsion cycle is appealing in theory. because leg power is continuous in many riding styles and environments.. If a mechanism can smooth out the drive characteristics—without demanding too much from materials. maintenance. or efficiency—it could change how power delivery feels. even if the overall ride remains fundamentally bicycle-like.
For makers and engineers. the project underscores a familiar reality: changing one part of a proven system can ripple into everything else.. Here. removing the crank isn’t only a question of mechanics; it forces new linkages between motion types. new drivetrain behaviors. and new tolerance requirements. all of which become visible when prototypes fail under load.
crankless bicycle 3D printed drivetrain mechanical rectifier bicycle engineering geartrain prototype alternative propulsion