Macroscopic robophysical model of biflagellate algae's phototactic turning

Algae exhibit diverse behaviors in their locomotion. For phototaxis, green-celled algae possess a light-triggered response that allows the turning of their eyespot towards a light source. The photoreceptor responsible for this type of behavior is well documented, however, the mechanical flagellar response is not. In Chlamydomonas, studies suggest that during a phototactic response, there is a change in beating frequency of the cis (the flagella closest to the eyespot) and trans flagella (Witman, 1996). To study phototactic turning, we developed a macroscopic motor-driven robophysical model that swims in a viscous fluid (glycerin, 1,100 cSt) to replicate low Reynolds number swimming. We achieve rotation by varying the frequency of the trans flagellum while maintaining a constant frequency of the cis. We observed that the efficacy of phototaxis depends on the phase position of the cis flagella. While the cis flagellum was in its recovery phase, the robot rotated 23-34 degrees per cycle (deg/cyc). While in the power phase, the robot rotated 8-13 deg/cyc. The results suggest turning dependence on flagellar coordination. Preliminary experiments suggest feedback control can be implemented in the robot to generate autonomous phototactic turning.