This is my entry for the "Search and Rescue 3D Printing' Design Contest".
This is the "Float" for the main assembly listed here.
https://www.shapeways.com/product/MSP8BRJJ2/phantom-4-sar-hub
4 of these are needed for one complete assembly. I'm not sure why it's so expensive, it's a hollow sphere with 2mm walls. Any similar sized plastic ball could be substituted at a fraction of the price. These parts are almost certainly very over-built and I'm confident the cost, weight and strength could be optimized. Please feel free to provide feedback!