agreed that combat robots had potential to be considerably more destructive than the pioneering machines on display. Their choice of weapon was a piercing arm attached to a hydraulic ram and powered by a pump, itself powered by a motorcycle starter motor. This was based on the principle of the fly press, a piece of machinery used to bend and pierce metal through progressive force. Razer's hydraulic system pumped pressurised liquid, as opposed to pneumatics where a force is generated by the controlled release of a pressurised gas. Razer's arm was often said to exert nine tonnes of force; however, it was the hydraulic ram which produced up to nine tonnes of pressure per square inch (1,395 kg/cm2, ) at its output, and this was geared down to three tonnes per square inch (465 kg/cm2, ) at the tip of the arm. Modifications This iteration of Razer competed in the second series of Robot Wars, successfully passing the Gauntlet and Trials stages of its heat before being defeated in battle by a robot called Inquisitor. The cause of Razer's immobilisation in this fight was the shearing of nylon cush drives—cushioning blocks designed to prevent stress fractures—in the machine's drive wheels; these were replaced with more robust metal ones for future competitions. As the Robot Wars television series evolved and grew, Razer's design was revised and refined to counter weaknesses and take advantage of rule changes; by series four, Lewis estimated that Razer had taken 1,500 hours to build, at a cost of £1,600. Razer's four-wheeled drive train used a skid-steering arrangement, whereby the wheels on one side of the robot rotated faster than those on the other to turn the machine. Also, the weight of the robot was biased towards the rear so that its weapon stayed facing its opponent as Razer turned. However, the solid rubber rear wheels used in series two provided too much traction and were reluctant to 'swing' the machine. For the third series, Razer used custom-made aluminium drive wheels which incorporated rollers, reducing the amount of force required for simultaneous forward and sideways movement. These wheels were later upgraded with a stronger titanium construction, whilst the level of oversteer in the drive system was reduced through the implementation of an electronic gyroscope. For the series Robot Wars Extreme II, Razer's rubber front wheels were replaced with metal ones bearing small spiked protrusions. Whereas competitors in