GM3: A General Physical Model for Micro-Mobility Vehicles

TL;DR

The paper tackles the lack of a unified, physics-based dynamic model for micro-mobility vehicles (MMVs) that captures tire slip, load transfer, and rider lean. It introduces GM3, a tire-level formulation built on the brush-tire model, supporting arbitrary wheel configurations and integrating load transfer and lean into a single framework, with a model-agnostic simulation environment for comparison against KBM. Key contributions include the GM3 formulation itself, an interactive simulation framework, and an empirical evaluation on the Stanford Drone Dataset DeathCircle showing improved ADE and competitive DFD relative to KBM across bicycle, skateboard, and cart modes. The work enables more realistic, tire-level MMV dynamics for training and validating autonomous systems in mixed-traffic environments, with practical implications for safer urban mobility and more faithful MMV simulations.

Abstract

Modeling the dynamics of micro-mobility vehicles (MMV) is becoming increasingly important for training autonomous vehicle systems and building urban traffic simulations. However, mainstream tools rely on variants of the Kinematic Bicycle Model (KBM) or mode-specific physics that miss tire slip, load transfer, and rider/vehicle lean. To our knowledge, no unified, physics-based model captures these dynamics across the full range of common MMVs and wheel layouts. We propose the "Generalized Micro-mobility Model" (GM3), a tire-level formulation based on the tire brush representation that supports arbitrary wheel configurations, including single/double track and multi-wheel platforms. We introduce an interactive model-agnostic simulation framework that decouples vehicle/layout specification from dynamics to compare the GM3 with the KBM and other models, consisting of fixed step RK4 integration, human-in-the-loop and scripted control, real-time trajectory traces and logging for analysis. We also empirically validate the GM3 on the Stanford Drone Dataset's deathCircle (roundabout) scene for biker, skater, and cart classes.

Figures (7)

• Figure 1: A tire modeled with physical parameters and brush model forces and moments.
• Figure 2: The GM3 State gets updated with the following steps: (1) load transfer and leaning angle to steer angle conversion for platforms, (2) control assignment for each tire, (3) individual tire processing with the brush model, and (4) force integration and rider lean force application.
• Figure 3: Bird's eye view of tire and body forces and moments for a two-wheeled MMV (bicycle or scooter).
• Figure 4: Diagram of rider center of gravity, roll moment, and centripetal force during leaning (a) and visualization with 2-wheel front-to-back layout (b).
• Figure 5: Skateboard with front and rear steering angles.