Fizzy: The underactuated robotic ball for interactive and engaging rehabilitation

Maintaining long-term engagement in physical therapy for pediatric and elderly people remains a clinical challenge. This work formally introduces Fizzy, a novel, low-cost, active, spherical robotic platform designed for rehabilitation and preventive healthcare in indoor unsupervised environments, integrating play with targeted exercise. Fizzy utilizes a single-motor, underactuated mechanism, to provide a simpler and more durable alternative to complex multi-actuator robotic ball designs. While this approach maximizes safety and accessibility, it introduces engineering challenges. This work shows the mechanical architecture and outlines the key technical foundations required for therapeutic integration.