Utterly Offensive Build Report (Robots)

A design that never got built

In light of the success of the current incarnation of Totally Offensive (success defined as [a] it wins and [b] it doesn't destroy itself in the process), I've decided to build a lightweight, 60lb version of the robot, currently named “Utterly Offensive”.

The Totally Offensive design seems to be pretty mature; the combination of the strong rear spar and the stiff but springy titanium box section that captures the Magmotor/Weapon gearbox works well and doesn't bend when it delivers its devastating “whack job” attack.

The fact that I don't have to build a new frame for T.O. after every event gives me the time and money to devote to the new project (or more precisely, it gives me a way to convince my wife to give me the money to build a new robot). I want to apply the lessons we've learned while building (and re-building, and re-re-building, and re-re-re-building…) T.O. to a heavier bot, while remaining true to the Totally Offensive philosophy of delivering insane amounts of shock and awe.

At the same time, I want to make improvements wherever I can. There are some clear weak spots in the T.O. design (in particular, the exposed wheels) that should be addressed in a new robot.

The first step in the design process was to determine what parts we could re-use in an Utterly Offensive design. As long-time readers know, I'm a big fan of the Whyachi T-Box drive gearboxes – and since I have plenty of spares, using them would be an obvious choice. The question is: can 2 T-Boxes, driven by Small Johnson (RS540) motors, push around a 60lb robot? Now, experienced engineers would be able to do the drivetrain and traction computations to figure this out, but because I haven't a clue as to how to do that, I just piled 40lbs of bricks on top of T.O. and tried to drive it.

Interestingly, it not only drives very well, but it drives better than T.O. does at 30lbs! The extra weight helps the wheels bite in and get good traction, at least on concrete - no wheelspin. So at first glance, it looks like they'll work. It's not like I plan to be pushing the other robots around much! If U.O. does need to push a robot around, it'll just have to bust it into 2 or 3 smaller bits first…


With that issue settled, it was time to play around with design and layout (click on the image to see a PDF). This time, instead of wrapping the robot around a S28-150 shorty MagMotor, the idea is to kick it up a notch and use its big brother, the S28-400. Furthermore, we will expand the titanium box structure and use it to store the batteries (which were stashed on top in T.O.).

Other changes in the design:

  • Room for up to 6 18v NiMH BattlePacks, so we can run at 36v or even conceivably 48v, though I have no idea if the motor can take that kind of stress!
  • 0.125“ Titanium plate (T.O. used 0.100)
  • Aluminum back spar (T.O. had a Ti one, but it was hard to make). Since U.O's spar does not

stick out from the main box, 6061 should be OK.

  • Outboard wheel bearings to help support the T-Box wheels when the robot does the bouncy-bouncy and comes down hard. These will incorporate an integrated Ti deflector to try and keep debris and enemy weapons away from the wheels.
  • 12.35lb 5” x 0.5“ x 22” blade spinning at 4900rpm if I'm insane enough to run the MagMotor at 48v. Will have ability to add teeth onto the blade tips. May go to a Ti blade with tool-steel teeth. If it turns out I don't need 6 battery packs, I'll be able to add blade weight. Note that 22“ is the same size as T.O's blade, so it can be used in an emergency.
  • Signature Self-Righting Hoop, just like T.O.
  • Since there's no battery box on top of the robot, it can be configured to run inverted with the blade on top (which I refer to as “Buster Mode” in honor of the elegant robot of that name).
  • As configured, 58.6lbs – way underweight by my standards.

Nothing is cast in stone at this point, but I hope to finalize the design after getting some feedback from other builders, and get it running in time for Motorama. I won't be able to compete there, but they might be dumb enough to let me spin it up in their box!

More details soon!