Concentric tube and steerable needle robots provide minimally invasive access to confined or remote spaces in the human body. While the modeling and control of these devices has received a great deal of attention in the robotics literature, comparatively less attention has been paid to date to the design of the mechatronic system that grasps the tubes/needles at their bases and applies axial twists and telescopic motions to component tubes, which we refer to as an actuation unit. Toward moving these systems to clinical use, this paper explores the design of a new, compact modular robotic actuation unit that incorporates new approaches to homing and tool changes. In particular, we accomplish homing using sensors that require no moving wires, eliminating potential failure points on the robot. We also present a new quick-connect mechanism that enables a collection of tubes to be rapidly coupled to or decoupled from the robot. This paper describes our new actuation unit design, illustrating our new tube coupling and homing concepts.