Movie S3.

Close-up movie on a collection of colloidal rollers (dark) propelling though lithographied obstacles (light patterns). The center of the cylindrical obstacles of diameter 10 μm are placed at random and may overlap. The lithographied obstacles repel the rollers at a finite distance, but leave their speed unaltered. Obstacle fraction: Φ_o = 15%. Colloid fraction ρ₀ = 0.08. Colloid diameter: 4.8 μm. Field amplitude: E₀ = 4.5V/μm. Video recorded at 190 fps, played at 25 fps.