Totally Offensive 2007 Build Report (Robots)
The 2006 Nationals was the first competition for the new version of Totally Offensive, and unfortunately, there were more problems than expected.
The biggest problem was that the blade tips were not designed correctly and shattered like glass, resulting in the ends of the titanium blades being pretty much mangled. Rather than junk them, I went back to the Solidworks drawing board and created a new, heftier tip design made out of big chunks of Chromoly that would slide over the remains of the current blades. The new versions would be a couple of inches shorter, but have similar KE due to the increased mass of the blades. After the new tips were machined by Team Whyachi, I prepared the blade ends on my Sherline mill (which required some cute fixturing, always a lot of fun). First, the slight undercut caused by the broadening of the waterjet that cut out the blades was eliminated, by simply painting the sides with marking fluid and milling in until it was all scraped off. Then the predrilled holes in the new tips were used as position templates to drill through the blades, the tip holes were tapped, and the new tips were bolted on. Finally, the remaining mangled stubs were chopped off.
I only had the short blade finished by Carolina Combat, but it performed extremely well, although it got a little blunted because it wasn't hardened. But after my experience at the 2006 Nationals, I'd rather take that than have them shatter.
The end result is that I now have a short blade for when TO wants to get up close and personal, a medium blade for when it wants to reach out and touch something, and a long blade for when the bot wants to go to great lengths to make the first impression.
On the electrical side, it was clear that the central chassis was far too crowded, so the victors that control the drive motors were relocated to expanded motor modules, right next to the T-Boxes. This makes them a little more vulnerable but anything that mangles them will also probably mangle the T-Box anyway, so I think it's a decent tradeoff.
The interior of the chassis was redesigned, with a new component that mounts the weapon victor above the battery, and has enough space for a fan to be mounted directly on the speed controller. The battery will be wrapped in foam, and the big powerpole connectors are on top of it, forming a layer on top of which the radio and its battery are mounted. I created a new radio battery connector using Deans connectors, as the plain-old Futaba connectors that had worked so well for me started flaking out at Carolina Combat. Finally, the holes for the original fans were covered with wire mesh, and the robot top plate was adapted so it also has a mesh-covered air vent just above the speed controller; the idea is that even if the fan fails, there will be some air circulation when the bot moves around.
Next, since TO goes through MagMotors like my kids go through Manga, I prepped another one by flatting part of the endbell (so it fit in the chassis, a cute hack invented by Nick Martin), and templated, drilled and tapped some bolt holes into it that are used to rigidly lock the endbell into the chassis.
Then, since Peter Smith borrowed TO's self-righting hoop to use on his Hobbyweight spinner, Surgical Strike, and then had the utter temerity to improve upon it (Peter, when my plans for World Domination come to fruition, you can forget about being named Duke of Raleigh!), I appropriated his improvement and added it to TO. The idea is to extend the hoop out a bit so that it attaches to the rear spar on an angle, and makes it easier to roll into wheel contact that then can be used to right the robot. The crucial insight Peter made was that by having the hoop attach to the chassis at an angle, the chassis makes a smaller slice into the unbalanced conic section that the hoop creates. Thus, by the time the chassis comes back into contact with the ground, it's much closer to vertical, and will self-right more easily.
After quickly making a set of adapter plates, since I didn't have a sheet-metal bender, I improvised and used a crescent wrench to roughly bend the plates, then squeezed them flat again in the vise. As you can see, it worked like a charm.
I also took the time to create an extra rear spar tube for the bot. There's a cute little tool for finding the center of a tube that comes in very, very handy (the Center Finder (part number 22025A11)), and once I had the central holes drilled, I used a strip of aluminum channel to create a fixture that ensures that the motor module mount holes are properly aligned.
And here is the final result. One nice side-effect of the larger hoop is that the robot can actually drive in a vertical position, a mode that was included in one of the earlier designs for TO (“Dutch Divine Wind Mode”). I doubt I'll actually use this is combat, but it would be pretty hilarious!
As always, your comments and suggestions are most appreciated.