Figure 6. The whisker taper is necessary for slips across textures.
(A) Dual-perspective imaging of a conical whisker, mounted on a galvo, sweeping across a texture (600 grit sandpaper). ‘Top’, Side view; ‘Bottom’, Top view. (B) Conical whisker swept past the texture at four distances: Free air, push distance dp = 0.33 mm, 1.5 mm and 4.5 mm. dp = ||x(Lw)−x(0), y(Lw)−y(0)||−d, where d is the nearest distance from the base of the whisker to the surface. In other words, dp is the distance the surface is moved radially into the whisker beyond just touching. Red traces indicate frames where the whisker tip is stuck, gray traces where the tip is slipping along the surface. Surface texture is schematic and exaggerated. (C) Black lines, histograms of tip position over time. Gray lines, trajectories of the whisker tip over the first three whisking periods. Traces are aligned to peak of theta at base. (D–F), as (A–C), but using a cylindrical hair of similar length. Free air, push distance dp = 0.33 mm, 2 mm and 3.3 mm. Whisker parameters Lw = 16.4 mm, rbase= 33.5 µm, rtip = 2 µm. Hair parameters as in Figure 4.