Aluminum is generally used as an ablative armor, so it performs the same function as UHMW. If you wanted something that would deflect hits to cover the UHMW, titanium or hardened steel are probably better. There really isn't much need for that, though. Many of us just use UHMW as armor on its own.
If you want to go with a UHMW unibody you'll need to know how to use a CAD program like Fusion, Inventor, or SolidWorks. If you have a CAD program and can design the chassis, I can help you with the rest. Saskatoon TechWorks has a CNC machine that does a great job on UHMW, and it's free for members to use. I'm a member there, so I can help you design toolpaths and learn how to operate the machine. If you want to pass on CAD for now and design on paper, then you'll probably want to go with a bolt together frame rather than unibody. I use a bolted together UHMW chassis for one of my 3lb drum spinners and a bolted together aluminum chassis for the other two.
For the drum, Sgt. Cuddles uses a direct drive drum, which is probably not something you'd want to make on your own for your first bot. Kitbots sells an off the shelf direct drive drum that's probably an easier solution. They also provide a chassis and internal parts for it if you want to start competing before finishing your first original design. FingerTech Robotics is another option. They sell a belt drive beater bar and all the accessories you'd need to get it running. And they're conveniently located in Saskatoon so you don't even have to pay shipping.
