Big Disk Energy Disk

The final part to design for Big Disk Energy was the blade. I actually procrastinated a lot on this part, it was designed after I built the rest of the robot.

While working on the rest of the robot, I learned about the robot Ripto. The blade profile on this robot gets exceptionally good bite because it is a single tooth, has good clearance between the tip and back of the blade, and is reversible so a single blade can last twice as long. I decided to base my blade design off of this profile because one of the goals for this robot is to get extremely good bite.

I started with a rough sketch of the profile and my hub motor bolt pattern. I started with a 25 degree positive rake and slowly increased it, watching the thinnest part of the blade. The back of the blade has a 0.75in clearance from the tip diameter, meaning that the theoretical maximum bite of this blade should be around 1.5".

This is a little unnecessary because 0.25in is the agreed upon threshold for good bite but I want to be completely sure that all impacts will be at the tip. This blade will not be nearly as strong at the back because it will be optimized only for a hit at the tip.

After messing around with some radiuses and tab thicknesses, I was able to get the stresses within the blade distributed pretty evenly and the CG of the blade within 0.0003" of the center of the bore. There is slightly more stress in the connection to the inner circle on the right so the failure mode of this blade should either be deformation of the entire blade or a fracture on the right side of the blade.

Here is the final product ready for waterjetting out of AR500. I added 0.005" clearance to the center bore and bolt holes to make sure the part will fit without any extra grinding.