From The TimeSplitters Wiki

Robot characters have appeared in all of the timesplitters games. In the games, they tend to be slow in movement. Most are large and bulky, but some like Gretel and ChassisBot are rather slender. In multiplayer, if character abilities are on, robots are unable to start on fire. They are able to when character abilities are off, and always are able to in virus. Robots are succeptible to the electrotool more than any other character. When the game is a robot, it will not be able to move when you shock it with the electrotool.