Swim2Real: VLM-Guided System Identification for Sim-to-Real Transfer
This work addresses the challenge of system identification and simulation calibration for soft underwater robots, which is hindered by strong nonlinear fluid–structure interactions and the sim-to-real gap. The authors propose the first use of a vision-language model (VLM) for underwater robot system identification, enabling end-to-end calibration of a 16-parameter fish-like robot simulator by directly comparing real swimming videos with simulation outputs—without requiring hand-designed search strategies. By integrating backtracking line search to improve parameter update acceptance rates, the method facilitates zero-shot transfer of reinforcement learning policies from simulation to the physical robot. After calibration, the mean absolute error (MAE) in swimming speed drops to 7.4 mm/s, a 43% improvement over the next-best method, with consistent convergence across five trials. Downstream RL policies achieve 12% and 90% greater swimming distances on the real robot compared to BayesOpt and CMA-ES baselines, respectively.