WAR Stop, which was equipped with a wedge.Halon gas – Rhino fought at the 1997 U.S. Robot Wars event with a halon gas fire extinguisher, which was very effective at stopping internal combustion engines. Gas weapons of this nature were promptly prohibited from future competitions.Pneumatic Cannon – First implemented by season eight Battlebots competitor Double Jeopardy, the robot fired off a 5-pound "slug" at 190 mph, exerting 4,500 pounds of force upon impact. This robot, however, did not perform well during its competition, as it only had one shot at landing a good hit: from there, it would have to rely on pushing its opponents, at which it failed. It subsequently upgraded its cannon to be more powerful and added the ability to fire more than one shot, though to this day, it has only one win under its belt. Unusual propulsion The great majority of combat robots roll on wheels, which are very effective on the smooth surfaces used for typical robot combat competition. Other propulsion strategies do pop-up with some frequency.Tank treads – Numerous combat robots have used treads or belts in place of wheels in an attempt to gain additional traction. Treads are generally heavier and more vulnerable to damage than a wheeled system and offer no particular traction advantage on the types of surfaces common in robot combat. Most uses of treads are for their striking appearance. The Robot Wars competitors Track-tion, 101 and Mortis along with the BattleBots super heavyweight Ronin used treads. Biteforce, the winner of the 2015 Battlebots Competitions, originally used magnets embedded in its treads in an attempt to gain extra downforce without extra weight.Walking – The spectacle of a multi-legged robot walking across the arena into combat is a big audience favorite. Robot combat rules typically have given walking robots an additional weight allowance to offset their slower speed, the complexity of the mechanism, and to encourage their construction. What the event organizers had in mind was something like the spider-legged robot Mechadon, but what most often was produced were simple rule-shaving propulsion systems that attempted to save as much of the extra weight allowance as possible for additional weaponry. Attempts at more restrictive definitions of "Walking" have effectively eliminated walking robots from competition. BattleBots heavyweight champion Son of Whyachi used a controversial cam-driven "Shufflebot" propulsion system, which was promptly declared ineligible for additional weight allowance at subsequent competitions.Gyroscopic precession –