A wearable drug delivery device that can deliver a liquid drug stored in a container to a patient is provided. The container can be a prefilled cartridge that can be loaded into the drug delivery device by the patient or that can be preloaded within the drug delivery device when provided to the patient. A sealed end of the container is pierced to couple the stored liquid drug to a needle conduit that is coupled to a needle insertion component that provides access to the patient. A drive system of the drug delivery device can expel the liquid drug from the cartridge to the patient through the needle conduit. The drive system can include a spring coupled to a plurality of force transfer elements. The force transfer elements can have a variety of shapes and configurations.