class. Heavier robots are able to exert more power and have stronger armor and are generally more difficult and expensive to build. Class definitions vary between competitions. The below table shows classifications for two organizations: the UK-based Fighting Robots Association (FRA) and the North American SPARC. Most televised events are of heavyweights. Its worth noting that the definitions of each weight category have changed over time - with European (FRA) rules for heavyweights advancing from 80kg, to 100kg, to 110kg over time. Currently Battlebots has a weight limit of . To encourage diversity of design, rules often give an extra weight allotment for robots that can walk rather than roll on wheels. Safety precautions Given the violent nature of robot fighting, safety is a central factor in the design of the venue, which is generally a sturdy arena, usually constructed of steel, wood, and bullet resistant clear polycarbonate plastic. The smaller, lighter classes compete in smaller arenas than the heavyweights. Competition rules set limits on construction features that are too dangerous or which could lead to uninteresting contests. Strict limits are placed on materials and pressures used in pneumatic or hydraulic actuators, and fail-safe systems are required for electronic control circuits. Generally off-limits for use as weapons are nets, liquids, deliberate radio jamming, high-voltage electric discharge, untethered projectiles, and usually fire. Robot fighting associations The sport has no overall governing body, though some regional associations oversee several events in managerial or advisory capacities with published rulesets. These include: Robot Fighting League (RFL), primarily U.S., operated 2002—2012 Fighting Robot Association (FRA), U.K and Europe, 2003–present Standardised Procedures for the Advancement of Robot Combat (SPARC), U.S., 2015–present The major televised competitions have operated outside of these associations. Combat robot weaponry and design An effective combat robot must have some method of damaging or controlling the actions of its opponent while at the same time protecting itself from aggression. The tactics employed by combat robot operators and the robot designs which support those tactics are numerous. Although some robots have multiple weapons, the more successful competitors concentrate on a single form of attack. This is a list of most of the basic types of weapons. Most robot weaponry falls into one of the following categories: Rammer – Robots employing high-power drive trains and heavy armor are able to use their speed and maneuverability to crash into their opponent repeatedly with the hope of