Abstract: A rotary force transfer mechanism includes an input (e.g., a pedal or handle) that receives a substantially linear input force (e.g., from a human operator), a rotary structure (e.g., a gear), and a drive element for selective coupling with the rotary structure to transmit the input force to the rotary structure to cause a corresponding rotary motion of the rotary structure. When transmitting the input force to the rotary structure, the drive element engages with an outer circumferential surface of the rotary structure such that the input force is transmitted to the rotary structure in a direction tangential to a position where the drive element is coupled to the rotary structure.