Testing an inverted pendulum model for underwater walking in the crab Carcinus maenus

Advisor Name

Olaf Ellers

Advisor Affiliation

Bowdoin College

Document Type

Conference Proceeding

Publication Date



Terrestrial walking has been well studied, but underwater walking has not. We use an underwater version of the inverted pendulum and a dynamic underwater Froude number to model underwater walking in the green crab Carcinus maenus. We model the motion of an underwater inverted pendulum taking into account buoyancy, added mass, drag and effective leg length of crabs. We overlay predicted theoretical time-dependent horizontal and vertical velocities over velocities measured for walking crabs. Crabs of varying sizes were videotaped while walking, and their centers of mass were tracked using image analysis software. The center of mass moves up and down, which is consistent with an inverted pendulum model of walking. The underwater Froude number is well within the range for a walking gait. The step frequency is also consistent with an inverted pendulum model modified for underwater conditions. The vertical and horizontal velocities at the ends of the strides, however, are clearly modified by forces from the legs.


Emily Norton was an undergraduate student at the College of William and Mary when this research was conducted.