The autonomous control period in VEX Competitions is currently 15 seconds and 45 seconds for VRC and VEXU respectively. During autonomous, the robot is controlled by pre-programmed controls rather than driver input from the VEX controller.
Although autonomous constitutes a small fraction of the total time in a match, this phase is the most challenging part of programming a robot (especially for newer teams). Due to differentiating field conditions, robot mechanical consistency, and driver setup among other factors are the reason for this.
BLRS (Purdue SIGBots)