Bike Crank Project

In a team of three, I designed a bike crank for a child's bike that would break at midway when a 12N is applied to the drive wheel. Through FEA analysis, hand calculations, and prototyping with acrylic and PLA, my team and I created a final product that prioritized torsional stress minimization and low mass.

This project was part of my Mechanics 3D Design course. In the project description, we were tasked with making a bike crank that breaks when a 12N force is applied to the drive wheel in order to prevent lower limb injuries in children that occur with high breaking maneuvers. The project required achieving a factor of safety of nearly 1.0 when a 12N deceleration force was applied, minimizing mass, and failing away from the interfaces. We were also given constraints of the size and shape based on the axle testing rig configuration shown to the left. Through hand calculations we estimated that the 12N deceleration force translated to a 9lbf applied at the load location.

My team's final design had a factor of safety of 0.8693. Our crank began to fail around 9-10lbf and broke completely at 11lbf. A detailed description of our design process and testing iterations is included in the pdf below.

BikeCrankProject.pdf