A Mobile Haptic Interface (MHI), a force-feedback haptic interface with a mobile base, allows to render very large virtual objects in a safe and portable manner. In this paper, we present a novel MHI system, featured with: 1) extended horizontal workspace using a omni-directional mobile base, 2) extended vertical workspace using a linear lift, 3) high-accuracy estimation of the position of the haptic interface tool, 4) efficient motion planning algorithm to move the mobile base while avoiding collisions with the user and other objects, and 5) closed-loop force control to compensate the undesired effect of mobile base dynamics on the final rendering force perceived by the user. As a consequence, our MHI system can provide high quality haptic rendering of large virtual objects.