The number of hopeful competitor robots far outnumbered the available slots in every series of Robot Wars (excluding Series 1). All unseeded competitors were required to undergo a screening process known as the Qualifiers, in order for them to appear on the televised show. The robots would perform in front of the Robot Wars staff, giving demonstrations of control and mobility for entry into Series 2 and 3, and battling against other hopefuls from Series 4 to Series 7.
For Series 2 and 3, robots had to knock a football into a goal, drive over a see-saw, drive around some breeze blocks, drive in a figure-eight around some large springs and then drive onto a piece of wood and spin on the spot.
For Series 4-7, the qualifiers assumed the form of one-on-one or melee battles between two or more prospective competitors. They would take place in a smaller version of the Robot Wars Arena, as the one seen on TV was too large to transport. The qualifier arena was painted to look like its televised counterpart, but did not usually include the hazards or the House Robots. Because of the arena's reduced safety capacity, roboteers were told not to flip their opponents out of the arena during their qualifier battles. The roboteers would be able to enter the qualifiers with more than one robot, but would only be able to qualify with one robot, this in particular affecting Team Mouse in Series 6 and 7, however Team Vader and Team Ming were able to enter with two robots each in Series 7.
The qualifiers always used the otherwise little-seen House Robot Shove as a cleaner/sweeper, as well as to push any immobilised/damaged robots to the arena entry gates if they could not be driven out on their own. Shove was used because it was more compact and easier to transport than Refbot.
For Series 8-9, no qualifiers took place. The qualification process for this series took the form of the producers reviewing applications sent in by potential entrants, and selecting them to compete. A number of robots that were not selected did eventually take part in an untelevised pilot episode, which was held and filmed with a live studio audience to test the camera equipment ahead of the main series.
The Robot Wars Wiki's list of known qualifier battles that took place from Series 4-7 can be found here, the wiki's list of known robots that failed to qualify for each series can be found here. Examples of Series 6 and Series 7 qualifiers can be found here and here.
As so few teams entered Series 1, no qualifiers were held for that series. In fact, there was actually a shortage of robots that were able to fight in the first series, as several robots suffered breakdowns etc. leading up to and during filming. As a result, three Stock Robots: Eubank the Mouse, W.Y.S.I.W.Y.G. and Grunt were used to make up the numbers.
Enough teams tried entering Series 2 to make having the qualifiers worthwhile. The qualifiers in this series featured a Gauntlet/Assault Course, similar to what they would have to face in the Heats and Semi-Finals, that the robots would have to complete.
Series 2 also saw the first occurrences of actual competitors coming in as reserves, for the robots that originally qualified but were unable to compete. Panda Monium, Wheelosaurus and Griffon were brought in to replace Cassius, Minotaur and Reckless Endangerment respectively. However, Cassius was able to participate in a later heat, and Minotaur and Reckless Endangerment were entered in the Super Heavyweight Championship at the end of the series.
To allow some of the robots that failed to qualify to compete in the televised show, a Reserve Rumble was held at the end of the series in the Grudge Matches, for five robots that were unused reserves to fight against each other. Despite this, there were still some robots, like RC Bandit and Team Power's Gnasher, that failed to qualify and didn't feature on the televised show at all.
Series 3 saw a considerable leap in the number of robots applying to participate, as 600 robots came to apply to feature on the televised show. It was not decided at the time of qualifiers that Series 3 would have no Gauntlet and Trial stages, so a Gauntlet/Assault Course was still used as a form of qualifier. As more robots were applying, the judging was much more strict than it was in the previous series. For example, some robots, like the original Major Tom, completed the course, but were still refused entry to the televised show.
Series 3 saw yet more reserves come into play, Binky, Flipper and Steg-O-Saw-Us replacing Daisy, The Parthian Shot and T-Wrecks respectively. There were other reserves, notably Wolverine, that still weren't used.
To allow some of the robots that failed to qualify to feature on the televised show, a handful competed in some of the side competitions held during the Third Wars, such as the Robotic Soccer and Pinball competitions. Some of these, such as Six Pac and Dominator, would prove especially competitive in these side events. However, some robots that did enter the main competition, including Evil Weevil, Razer and Killerhurtz were still used in Robotic Soccer and Pinball to compare these non-qualifiers to those that qualified for the main series.
A record-breaking "Over 1000" teams applied for this series. Because the format of the show had changed to combat-only, the qualifiers now consisted solely of head-to-head battles between hopeful competitors, which gave the possibility of draws being declared in the event that there was no clear winner. Some robots were able to fight more than one battle. All thirty-two of the seeds for this series qualified automatically.
The Series 4 qualifiers were held as a live event, the first large-scale one of its kind, called "Robot Mayhem". The event went on for two weeks, with six battles per day. The House Robots would be used in the qualifiers. As well as the qualifier battles, the House Robots and some seeded robots such as Razer and Hypno-Disc would give demonstrations.
Due to some of these battles being decidedly "boring" battles, even robots that won their qualifier battles were refused entry into the televised show, such as Dantomkia 1.0. Conversely, robots that lost their qualifier battles, like Warhog, were given discretionary places into the main competition, as they put on a more entertaining show.
V-Max, which originally failed to qualify, was selected as a reserve, and replaced Onslaught after it withdrew from the main competition in the last minute. There were other reserves for the Fourth Wars, notably Charybdis, that were not used.
Unlike the Third Wars, no robot that failed to qualify participated in the side events that were held during the filming of the main competition.
The Fourth Wars also saw the first instance since the First Wars of a robot being able to qualify without having to go through the Qualifiers. Scorpion was granted automatic entry, as the Robot Wars producers decided that it would look appealing in the arena.
The Series 5 qualifiers were also done in front of a live audience to promote the upcoming series. Unlike the Series 4 qualifiers, the live events for the Series 5 qualifiers were held at various locations as a live tour, at places including Glasgow, Cardiff, London and Newcastle. This time, Craig Charles was used as MC, whilst the House Robots were put into the arena again for the qualifiers. Most of the battles were still head-to-heads, but melees were often used to quicken the judging and selection process.
At the time of the qualifiers, the top 16 seeds had been decided, but as the number of seeds was reduced from 32 to 24, the remaining eight seeds were decided during the qualifiers. Like the previous year, seeded robots such as Razer and Chaos 2 still attended the qualifiers as static displays and to give demonstrations to the audience.
Winning a battle still did not guarantee a robot's place in the main competition. Robots such as Cataclysmic Variabot and Barbaric Response failed to qualify despite winning their battles. Conversely, some robots that lost their battles, such as Dome, were awarded discretionary places.
Some robots, such as Spirit of Knightmare and Arnold A. Terminegger, despite failing to qualify for the Fifth Wars, would still enter competitions in the first series of Robot Wars Extreme, which was filmed at the same time as Series 5.
At many of the qualifiers, robots were put into groups of four. There would be two one-on-one first round battles, and the winners would then fight each other, the winner automatically qualifying for Series 5. For example, S3 and Dynachrome fought two other robots each before facing off against each other; S3 won the battle and automatically qualified.
For the Sixth Wars, the qualifiers were mostly four-way melees, like the first-round battles in the televised show, however some consisted of only two or three robots depending on availability. Unlike past series, each robot was strictly limited to one qualifier battle, and the winners would be guaranteed qualification. However, losers could still be awarded discretionary places.
Notably, future series champions Typhoon 2 would fail to qualify for this series, after losing its qualifier battle.
8645T 2 was disqualified from the qualifiers after its axe damaged the arena floor.
Some robots, such as Lightning, Cerberus and Typhoon 2, despite failing to qualify for the Sixth Wars, would still fight in competitions in the second series of Extreme, filmed a few months later that same year. In particular, robots such as Mad Dog, Chip and Pressure got their first chance to appear on the show in the New Blood Championship, broadcast as part of the latter.
In Series 7, the qualifiers were the same format as those of Series 6 - up to four-way melees with qualification guaranteed to the winner(s), and others being granted discretionary places. Around 200 robots attempted to qualify for this series.
For the first time in the UK championship, teams from outside the UK attempted to qualify. Twenty-two roboteers from eastern and central Europe pooled their money for transportation to the qualifiers. Arthur Chilcott of Random Violence Technologies even allowed them to use his backyard as a camp-ground. Of the teams that failed to qualify, some of those would still fight for the right to enter in the Third World Championships, held at the end of the series.
Oddly, Typhoon 2 lost its second consecutive qualifier, this time to Ewe 2, losing alongside Big Nipper and Araknia, but Typhoon 2 was this time given a discretionary place for the Seventh Wars, as were Big Nipper and Araknia. Typhoon 2 would then go on to win the series.
Once again, Team Mouse were forced to only qualify with one robot, this time opting for Velocirippa, but Mighty Mouse was still listed as a reserve due to the team living nearby to the studio and being able to make it to filming in a short amount of time.
There were some occurrences during the Seventh Wars where reserves could/should have been brought in, but were not. Terrorhurtz was disqualified from its heat due to a behind-the-scenes technicality, while Thunderpants was red-carded by Refbot after it was unable to leave its entry gate just before its first round battle. In both cases, no reserves were allocated to take their places, and the first-round battles they were scheduled to fight in began without them. Tanto had been considered as a reserve, but for unknown reasons was not brought in to fight when Thunderpants broke down.