Design, Modeling, and Control of Unicycle Robots: A Systematic Literature Review

Unicycle robots pose significant challenges due to their single-wheel configuration, underactuation, and nonlinear dynamics. These characteristics require sophisticated balancing mechanisms and control strategies. Given these complexities, this paper presents a Systematic Literature Review (SLR) of unicycle robots. The review synthesizes advancements in balancing mechanisms, robot modeling, sensor integration, and control strategies from January 2014 to December 2024. This systematic review is conducted using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology to ensure a comprehensive and unbiased evaluation of the literature. We selected and analyzed 56 peer-reviewed studies from four major databases. Our objective was to systematically identifying, categorizing, and evaluating task-level performance (e.g., stability, tracking, and recovery) and robustness evidence reported across studies. The findings reveal that most studies address stabilization, motion control, and self-recovery as separate tasks, with limited integration into a single control architecture. Furthermore, experimental validation remains limited, with many approaches relying on idealized models or simulation-only testing, which highlights the gap between theoretical design and real-world application. To ensure up-to-date relevance, the Discussion considers selected studies published in 2025 beyond the PRISMA window. Through the analysis of key research trends, this review provides a detailed overview of advancements in unicycle robot development and highlights directions for future exploration. These insights provide a foundation for more robust unicycle robot systems capable of operating under realistic constraints.