You can think of it as politically correct boxing. Instead of two men squaring off to draw each other's blood, fast little remote-controlled vehicles do the fighting. They can get banged up, but nobody gets hurt.

The matches have a following. The Comedy Central cable network in the United States tapes competitions in California, where the sport is administered by BattleBots Inc. of Novato, Calif. "Robot Wars," based in Britain, is broadcast in more than two dozen countries. A Web search can return hits for robot sumo matches in Japan.
Robots may ram, hammer, cut, buzz, claw, or club. Some are designed to push opponents into hazards or turn them over to disable them. Some deliver blows and upset their opponents by spinning weapons like blades or discs.

A new spin put William McHargue of San Diego into the game. A freelance physicist, McHargue came up with a BattleBot entry that has two powered wheels, which can be propelled in opposite directions to spin the entire body of the robot at about 600 rpm, putting all of its mass into play.

McHargue had observed other designs that place a spinner on a carriage, which does not figure in striking power.

The difference in McHargue's design is that it uses the wheels to spin the robot and to travel at the same time. Braking a wheel for about 50 milliseconds at just the right point of the machine's spin will make the robot inch in the direction perpendicular to the axis of the motor at the time. With the right control, the machine can travel anywhere in the ring.

The inset wheels of this BattleBot rotate in opposite directions for offensive spin. Controlled braking steers the machine around the ring.

McHargue's normal work helps companies such as Recording Physics and Found Image Press overcome challenges in the areas of physics, electronics, and system design. He designed and built the robot on his own, without the assistance of a staff of engineers and detailers.
McHargue's design uses 32 lead-acid batteries that together can produce a total of 240 amps for one minute.

Two 3.9-horsepower electric motors draw the full power of the batteries briefly at the beginning of the match to accelerate the robot to a rotational speed of 600 rpm, and then the current draw drops to between 20 and 30 amps.
The control system needs to drive each motor, then shunt its armature, up to 10 times a second, in order to move the robot. McHargue used 1970s-era CMOS logic circuits and a total of 32 100-amp field effect transistors to perform the switching. He used an infrared control system instead of the common RF because it provides an orientation signal that is critical to the operation of the control system.

"The robots start at opposite ends of the arena and it takes only a few seconds before they reach each other," McHargue said. "I needed to keep the moments of inertia low enough so I could get up to a defensible speed of 200 rpm before the other robot reached me. On the other hand, I wanted the peak energy to be high enough to smash the other robot apart."

McHargue designed the robot with 3-D solid modeling software called Cobalt from Ashlar-Vellum of Austin, Texas. He transported mass and density distribution information from Cobalt into Mathematica, technical computing software from Wolfram Research Inc. of Champaign, Ill., to predict the performance of the finished machine.

McHargue's robot, Tesla's Tornado, competes in the middleweight division of BattleBots, with others up to 120 pounds. (Super-heavyweight runs up to 325 pounds.)

Tesla's Tornado delivered knockout blows in its first two competitions last November at Treasure Island in San Francisco. McHargue said he had some problems during those matches in getting the robot to translate across the floorÑapparently because of multipath IR (that's infrared, not Injured Reserve) reflections. Tesla's Tornado was eliminated in the third match by a decision. The other bot had a pickax that made several good strikes, but did not do any real damage.

McHargue has refined the design with smaller motors that deliver the same power but weigh less. That allowed him to add cutters at the corners of the Tornado's rectangular frame. They are made of S7 tool steel hardened to Rockwell 57C, he said. Tesla's Tornado now weighs 118.5 pounds, 1.5 below its upper weight limit.

At a second competition this past May, the Tornado didn't start up for its first bout. McHargue isn't sure why. The robot had power, he said, and other systems were apparently working. "It has never happened before or since," he said.

Although he was disappointed, he had some consolation in being able to use the BattleBots' new testing arena to practice, where Tesla's Tornado did just fine.
McHargue said that the Tornado will be back in November.

home | features | weekly news | marketplace | departments | about ME | back issues | ASME | site search

© 2002 by The American Society of Mechanical Engineers