Mathematica and BattleBots

Bringing Aggression, Determination, and Mechanical Engineering to a Living Room near You

Looking for action with brains-over-brawn appeal? William McHargue, a freelance physicist and long-time Mathematica user, is one of many who find this combination in BattleBots, the new fighting-robot craze. "With BattleBots, one can be aggressive and yet nobody gets hurt," says McHargue. Recently, McHargue was featured in Mechanical Engineering magazine for work on Tesla's Tornado, his BattleBot.

BattleBots have hit the mainstream, thanks to their popular television series, which is currently in its fifth season. More than just a TV show, BattleBots Inc. holds the best-known fighting-robot tournament in the United States. Fans can find a wide array of BattleBots merchandise including figurines, books, magazines, video games, and clothing. The tournaments provide a forum in which builders exhibit their ingenuity and expertise. BattleBots also challenges fans to join the builder subculture with online tips and guidelines for creating BattleBots of their very own.

Many BattleBot builders work in teams of three or more, but McHargue chose to design and construct Tesla's Tornado on his own. Degrees in physics, electrical engineering, and computer science made him particularly well equipped to undertake the entire robot-building process. Although Telsa's Tornado hasn't yet been featured on television, McHargue did rack up wins in his first season when the BattleBot delivered knockout blows to its opponents.

In the BattleBox, Tesla's Tornado is a 117.9-pound block of spinning, smashing steel. This BattleBot is so effective at wreaking mass destruction that testing the robot outside of the reinforced bulletproof BattleBox is impossible. That's why McHargue turned to Mathematica to model the efficiency of his creation before he even began construction.

McHargue first modeled Tesla's performance with Mathematica using masses predicted by Cobalt, a solid-modeling program. "Mathematica was employed to help predict the basic performance of the finished robot," McHargue says. Then, as McHargue finished crafting each component, he incorporated the actual masses into the Mathematica model. Now, when McHargue wants to make changes to his BattleBot, all he has to do is to plug the new data into his existing Mathematica model.

McHargue's design philosophy is "to make a fighting robot as simple as possible, yet still effective in combat." Tesla's Tornado, a competitor in the 60-to-120-pound middleweight division, appears rugged but harmless when sitting still. Instead of elaborate contraptions such as the hammers, saws, and axes used by other competitors, Tesla's secret weapon is its rotational inertia. To ensure Tesla's effectiveness, McHargue graphed its rotational speed versus time from start-up with Mathematica. "I needed to know ahead of time whether it could spin up in a short enough time frame to defend itself," he says.

McHargue eliminated the turntable used in most "horizontal spinner" bots and instead made the whole body the spinner. This puts Tesla's full weight behind its spin, and at speeds surpassing 600 rpm, it can inflict some serious damage. At full speed, Tesla's Tornado can exert a 28-millisecond impulse of nearly three tons when its bot cutters strike a 120-pound opponent. "It is this kind of high, if only short-lived, force that can break things," says McHargue.

In order to implement his innovative "chassis is weapon" design, McHargue engineered the two powered wheels to perform multiple functions. First, they spin in opposite directions with substantial torque to ensure that the bot will accelerate to at least 200 rpm in three seconds, the amount of time it usually takes opponents to cross the ring and attack. Then, to move around the ring, each wheel brakes at specific intervals in the spin. When a wheel is braked, it acts as a pivot point, resulting in bursts of carefully directed momentum, which cause the bot to translate (move laterally) as directed by remote control. Since Tesla's wheels are continuously running at high speeds, it can function only on surfaces as smooth as the BattleBox floor without rapidly wearing out the tires.

Adding to the experimental nature of his design, McHargue's control scheme is also unique. He has created the only BattleBot that is controlled by infrared light. Using light instead of radio waves provides a reference for the braking that allows Tesla to translate. Converting the light source to a laser is on the drawing board for his next competition. BattleBots safety regulations required him to perform an analysis to prove that the laser would not harm anyone viewing the fight. McHargue performed the calculations for this analysis and typeset the report using Mathematica.

"The quality and robustness of the Mathematica system, the fact that Wolfram has never stopped supporting Macintosh (my platform of choice since 1984), and the publication quality of its PostScript output are but a few reasons I first turn to Mathematica when considering problems of a general scientific or engineering nature," says McHargue. He also enjoys the ability to carry units throughout all of his calculations. This helps guard against accidentally overestimating Tesla's performance. McHargue notes that although he could have done these calculations with other software tools, the notebook environment's ability to use full symbolic expressions in actual equations and to mix plots right in with everything else "just makes Mathematica a better tool."

BattleBots airs on Saturdays at 8 p.m. Eastern Standard Time on Comedy Central. For more information on BattleBots, check out the BattleBots.com website.