Hello Everyone! Today’s installment of Spencer’s blog is being written by Halo’s second part, Pierce! I’m the brains behind the mechanical design and implementation of Halo, along with sanity checking all of Spencer’s work. I wanted to write this blog post to discuss the weakest point of the bot from the previous competition: The ring.

The Ring

The chassis of Halo is a unibody construction of 6061-T6 aluminum. We started with a 10” diameter by 1/2” wall aluminum tube that I turned down on my work’s manual lathe. I machined it into a C profile to help reduce the weight. The thickness of the wall is just over 1/8 of an inch thick. We discovered that we were overweight on the initial turning, so I reduced the weight of the ring by approximately 0.25 pounds by adding a 1/4” chamfer at the edges of the bot. This reduced the overall weight of the ring to just under 1 pound. The chamfer is not ideal because it pushes wedges underneath us, but the rapidly approaching impactor helps knock away our problems.

Because of the thin nature of the ring, it introduces us to some structural problems.

The First Impactor

Our first design worked surprisingly well. The first tooth was just a small chunk of 1/2” A36 steel plate that had been trimmed down to save some weight. It was secured to the ring by two grade 5 1/4"-20 hex head bolts. I was immediately worried that the bolts may rip their way through the ring, or crack it in half. Needless to say, I was flabbergasted when the ring survived all the way through the competition. By the end of the competition though, it was cracking right at the base of the impactor.