This is a real world project. I'm building a giant roll-up window shade to be used for a special effects green screen. The first real model attempt (without math) failed. See the two pictures of the tube structure being held up by chairs. The only axle was about 3ft of 1.5" pipe at each end. The rest is 8" diameter concrete tubes. We double walled the tubes by slicing the length of one and using it as a coupler inside to hold two tubes end to end. We made about twelve 3/4" wooden disks to help support the structure and secure to the axle. Deflection in the middle was too great. Second attempt in next post.