In one embodiment, an injector includes a sleeve, a drive assembly, and a drive assembly housing. The sleeve is configured to receive a reservoir having a plunger therein. The drive assembly is configured to pressurize the reservoir and includes a tip, an actuator, and mechanical segments. The tip is configured to be secured to the plunger. The actuator is configured to supply a motive force to the tip for moving it between retracted and extended positions. The mechanical segments are configured to transmit motive force from the actuator to the tip. The drive assembly housing has a housing length in a direction parallel to a central longitudinal axis of the tip. The reservoir has a reservoir length L. A package length is defined by the housing length and the reservoir length L. The package length is less than 2L.