Overview

Cal Poly Bike Builders and professor Andrew Kean sponsored my senior project along with Colin Reay, Robby Harrigan, and Jordan Olson. At Cal Poly, senior projects last one year and aim to give students experience with design, manufacturing, documentation, management, and team work.

Our goal was to design and machine affordable chainstay yokes club members to use on personal bikes. Chainstay yokes are a machined component that allows for larger tire, chainring, and crank arm clearance than traditional chainstays. You can buy them, but they are prohibitively expensive for most club members. We designed the yoke, did comparative strength and stiffness analysis, machined straightforward and repeatable fixturing, and designed and manufactured test fixtures.

Design and Analysis

Because bicycle loads are so hard to quantify, our group decided to do comparative analysis for strength and stiffness. We made a Fusion 360 model with 3D models of off the shelf yokes from Paragon Machine Works, Cobra Framebuilding, and others. We referenced ISO 4210 loading conditions for bike frame stiffness tests which are widely used in the bike industry.

After analysis and qualitative comparison, we decided on a Paragon Machine Works style CNC machined clamshell yoke. This design suits our manufacturing capabilites, it's easy for club members to fixture into their frames, and it's customizable. 

Manufacturing

We designed two fixture plates: one for machining raw stock in Op 1 and the second for finishing the yoke in Op 2. Both fixture plates locate on a common baseplate.

Testing