An injector comprising: an injector housing having a base housing portion defining a skin contact surface ; a chassis attached to the base housing portion ; an injection needle supported by the chassis , the injection needle being movable with the chassis relative to the base housing portion from a retracted position, wherein at least a tip of the injection needle is contained within the base housing portion , to an injection position, wherein at least the tip of the injection needle protrudes from the base housing portion ; at least one rotary biasing assembly stabilized in a stored energy state and releasable into an energy releasing state, the at least one rotary biasing assembly including a cam ; and characterized in that it further comprises at least one cam follower corresponding to the at least one rotary biasing assembly , the at least one cam follower coupling the at least one rotary biasing assembly with the injection needle and being configured to transform rotation of the at least one rotary biasing assembly in the energy releasing state thereof into translation of the chassis and the injection needle , relative to the base housing portion , from the retracted position to the injection position; an activation switch coupled with the chassis and rotatable from an unactivated position, stabilizing the at least one rotary biasing assembly in the stored energy state thereof, to an activated position, releasing the at least one rotary biasing assembly into the energy releasing state thereof; and an activation button movably mounted to the injector housing , the activation button being translatable from an unactuated position to an actuated position, wherein translation of the activation button from the unactuated position to the actuated position rotates the activation switch from the unactivated position to the activated position thereof. an injector housing having a base housing portion defining a skin contact surface ; a chassis attached to the base housing portion ; an injection needle supported by the chassis , the injection needle being movable with the chassis relative to the base housing portion from a retracted position, wherein at least a tip of the injection needle is contained within the base housing portion , to an injection position, wherein at least the tip of the injection needle protrudes from the base housing portion ; at least one rotary biasing assembly stabilized in a stored energy state and releasable into an energy releasing state, the at least one rotary biasing assembly including a cam ; and characterized in that it further comprises at least one cam follower corresponding to the at least one rotary biasing assembly , the at least one cam follower coupling the at least one rotary biasing assembly with the injection needle and being configured to transform rotation of the at least one rotary biasing assembly in the energy releasing state thereof into translation of the chassis and the injection needle , relative to the base housing portion , from the retracted position to the injection position; an activation switch coupled with the chassis and rotatable from an unactivated position, stabilizing the at least one rotary biasing assembly in the stored energy state thereof, to an activated position, releasing the at least one rotary biasing assembly into the energy releasing state thereof; and an activation button movably mounted to the injector housing , the activation button being translatable from an unactuated position to an actuated position, wherein translation of the activation button from the unactuated position to the actuated position rotates the activation switch from the unactivated position to the activated position thereof. <EOS>