The Series 4 Robot Wars Set was the fourth incarnation of the Robot Wars Arena, designed by Julian Fullalove, who replaced Steve Clark as the lead designer. Both The Fourth Wars and the unaired MTV Pilot were filmed at Park Street Studios, less than ten minutes away from Elstree Studios, where the previous series was filmed. At the end of Series 4, filming was moved back to Elstree Studios for Series 5/Extreme 1; not long afterwards, Park Street Studios was sold off, before going bankrupt in 2003.
The Series 4 arena once again underwent a complete redesign, with substantial changes made between it and the arena used in Series 3.
As with previous incarnations, the Series 4 arena consisted of a large rectangular base with a plywood floor. Several changes were made to the arena from its Series 3 form; firstly, the metal barriers were replaced with a wall made from sections of bulletproof glass, with the intention of improving safety. Additionally, the scrap metal sculptures found in previous series were replaced by large spotlights, while the balcony and back wall received a noticeably different design resembling the interior of a military submarine. Meanwhile, the cherry pickers where competitors controlled their robots in Series 3 were replaced with static booths that allowed teams access to the balcony for post-battle interviews.
Competitor and House Robots would now enter the arena through one of three entry gates located beneath the balcony and control booths. Each featured large sliding doors and a smaller gate which also formed one of the bulletproof wall panels, both connected by a flat-floored section where robots could be driven in and out of the arena. For battles, the doors would remain closed and the gates would be raised to the same height as the other wall panels. The central gate formed part of the large Robot Wars logo - a prominent design feature since Series 1 - and retained the set of sliding doors featured in previous series. It was also used by roboteers to enter the arena and collect their trophies upon winning a main or side competition in this series.
The arena's colour scheme received a substantial overhaul, with a grey floor and most of the arena hazards being marked out in yellow and black hazard stripes with red borders. Lighting was a mix of blue, purple, pink, white, orange and yellow, carrying over the mysterious aura evident in Series 3.
The Series 4 arena featured few completely new hazards, with the majority of the existing hazards instead being carried over with considerable mechanical and cosmetic changes. However, the arena floor spikes, which attracted controversy in Series 3, were discarded.
- The Corner Patrol Zones (CPZs) remained in each corner of the arena, patrolled by one of the House Robots and marked in yellow and black hazard stripes with red borders. The introduction of Refbot in this series marked a change in how the House Robots could attack other robots, in that they no longer had the freedom to leave their CPZs until a competitor was confirmed to be immobilised.
- The Pit of Oblivion featured substantial changes, now consisting of a panel in the floor painted in yellow and black hazard stripes with a red border. In every battle, the pit panel would initially sit flush with the floor in the raised position, before descending after a certain amount of time elapsed. This time varied as the producers saw fit (the video game Robot Wars: Arenas of Destruction, based on this series, has the time set at a fixed 1:40). A siren sound effect was added to herald the pit's descent, although no such sound was actually audible in the arena during filming. As in Series 2, smoke plumes would fire from within the pit whenever a competitor robot fell in, instead of sparks as in Series 3.
- The Floor Flipper received major improvements, featuring the same markings as the Pit and being made larger than before. The Flipper also received more powerful pneumatics which enabled it to throw defeated competitors over more easily, sometimes even throwing them across the arena. The hazard was known as the Evil Ejector during the Series 4 Celebrity Special.
- Fire hazards were the most common from within the arena - the established Flame Pit was supplemented by flame jets spouting single jets of fire from the arena floor, along with flamethrowers lining the side wall underneath the balcony. As with the previous series, these hazards proved reasonably effective in burning out internal components and setting fire to robots featuring flammable materials, although they were generally ineffective against most competitors.
- Sets of static and retractable spikes also lined the arena walls, which supplemented the circular saws found in Series 3; the latter referred to in this series as grinders. However, the spikes would be discarded completely by the time of the arena's next redesign.
- Spouts of CO2 were also featured near the CPZs, although these were mainly used as atmospheric hazards.
As with the main battle enclosure, the arena perimeter also received major changes, although traces of the older Series 3 set are visible. Most of these changes were carried out to improve the safety of the audience, following the introduction of more powerful rotating weapons such as Hypno-Disc's disc in the previous series.
The balcony itself remained the same as the previous series, but the backdrop was changed to give the arena a more military feel. More noticeably, two static control booths replaced the cherry pickers formerly used, which were more spacious and provided better protection for the roboteers through using bulletproof glass windows.
At the end of most battles, Craig Charles would interview competitors on the balcony, as he had done in Series 2. With the balcony potentially having to accommodate Charles, two or more teams of up to three members each, plus camera crews, this arrangement caused considerable problems with the balcony being cramped and lacking enough space for the teams to move around in. Certain interviews held throughout Series 4 especially highlighted this issue.
Safety provisions were much improved for Series 4, with several new measures being introduced in response to behind-the-scenes accidents which occurred in earlier series and resulted in the retirement of Rex Garrod. The audience was now placed behind a large plexiglass case surrounding the entire arena, as well as a crowd control barrier preventing them from getting too close to the edge of the arena. Between the outer case and the inner arena walls, a flip-out zone was also evident, where competitor robots would end up in after getting flipped over one of the walls.
Changes from the Previous Series
- The pit and floor flipper were covered in yellow and black markings.
- The pit again fired a smoke screen instead of sparks, and descended after a certain amount of time.
- Booths replaced cherry pickers.
- Flame jets were placed on the arena floor.
- Flamethrowers lined the arena wall.
- The entire arena was now surrounded in plexiglass for safety reasons.
- The scrap metal sculptures were discontinued.
- The floor spikes were discarded.
- Sets of static and retractable spikes lined the arena wall along with circular saws.
- The floor flipper in Series 4 had two different mechanisms.