This paper presents a (patent-pending) small, quasi-static, minimal-complexity Stair Climbing Robot (SCR). The vehicle design is given simply by adding a third motor to a (Segway-like) Mobile Inverted Pendulum (MIP), enabling it to maneuver up stairs, leveraging feedback control, by planting it's “foot” onto the ground in front of the next step, lifting the chassis/wheel assembly up it's own “leg”, leaning over onto the top of the next step, self uprighting, and repeating for the following step(s). Fore/aft stabilization during leg balancing is given by using the MIP drive wheels as reaction wheels, while left/right stability is given by the width of the foot itself. The design is small and simple enough to potentially be ruggedized as a stair-climbing throwbot, akin to the Recon Scout (but able to climb up stairs) for reconnaissance in military and homeland security applications.

Ball-balancing robots (BBRs) are endowed with rich dynamics. When properly designed and stabilized via feedback to eliminate jitter, and intuitively coordinated with a well-designed smartphone interface, BBRs exhibit a uniquely fluid and organic motion. Unlike mobile inverted pendulums (MIPs, akin to unmanned Segways), BBRs stabilize both fore/aft and left/right motions with feedback, and bank when turning. Previous research on BBRs focused on vehicles from 50cm to 2m in height; the present work is the first to build significantly smaller BBRs, with heights under 25cm. We consider the unique issues arising when miniaturizing a BBR to such a scale, which are characterized by faster time scales and reduced weight (and, thus, reduced normal force and stiction between the omniwheels and the ball). Two key patent-pending aspects of our design are (a) moving the omniwheels to contact the ball down to around 20 to 30 deg N latitude, which increases the normal force between the omniwheels and the ball, and (b) orienting the omniwheels into mutually-orthogonal planes, which improves efficiency. Design iterations were facilitated by rapid prototyping and leveraged low-cost manufacturing principles and inexpensive components. Classical successive loop closure control strategies are implemented, which prove to be remarkably effective when the BBR isn't spinning quickly, and thus the left/right and fore/aft stabilization problems decompose into two decoupled MIP problems.