Mechanical properties of a bio-inspired robotic knifefish with an undulatory propulsor

Abstract

South American electric knifefish are a leading model system within neurobiology. Recent efforts have focused on understanding their biomechanics and relating this to their neural processing strategies. Knifefish swim by means of an undulatory fin that runs most of the length of their body, affixed to the belly. Propelling themselves with this fin enables them to keep their body relatively straight while swimming, enabling straightforward robotic implementation with a rigid hull. In this study, we examined the basic properties of undulatory swimming through use of a robot that was similar in some key respects to the knifefish. As we varied critical fin kinematic variables such as frequency, amplitude, and wavelength of sinusoidal traveling waves, we measured the force generated by the robot when it swam against a stationary sensor, and its velocity while swimming freely within a flow tunnel system. Our results show that there is an optimal operational region in the fin's kinematic parameter space. The optimal actuation parameters found for the robotic knifefish are similar to previously observed parameters for the black ghost knifefish, Apteronotus albifrons. Finally, we used our experimental results to show how the force generated by the robotic fin can be decomposed into thrust and drag terms. Our findings are useful for future bio-inspired underwater vehicles as well as for understanding the mechanics of knifefish swimming.

Mutually opposing forces during locomotion can eliminate the tradeoff between maneuverability and stability

“…We used a biomimetic knifefish robot (29,31) to measure forces generated by counterpropagating waves as well as to assess freely swimming control strategies in one dimension. Mechanical design constraints limited us to a larger length scale and longer time scale than Eigenmannia.…”

Kinematics of the ribbon fin in hovering and swimming of the electric ghost knifefish

“…Our prior computational and robotic studies indicate that the observed number of undulations (two to three) generates maximal thrust (Shirgaonkar et al, 2008;Curet et al, 2011b). Below this number of undulations, although the wave velocity increases, the amount of force in the surge direction decreases (in the limit, with zero undulations, all the force goes into the vertical, or heave, direction).…”

“…In prior studies, we have used computational fluid dynamics and a bio-mimetic ribbon fin robot to quantify how force magnitude and direction varies with most of the kinematic variables considered here (Shirgaonkar et al, 2008;Sefati et al, 2012;Curet et al, 2011a;Curet et al, 2011b). It is therefore useful to consider the implications of our kinematics results in light of those findings.…”

“…This maneuverability occurs despite holding the body axis semi-rigidly straight. Besides being a useful system for understanding the fundamental mechanical principles of multi-directional agility, high maneuverability with relative axial rigidity forms a compelling basis for inspiring new designs for underwater vehicles (MacIver et al, 2004;Curet et al, 2011b).…”

Investigation of Fish Caudal Fin Locomotion Using a Bio-Inspired Robotic Model

“…As many recent studies have reported that fish can actively deform their fins to achieve different types of locomotion, more and more researchers have realized the importance of these flexible propulsion surfaces on enchancing ability of swimming. Such propulsion surfaces include dorsal fins [2][3][4] and pectoral fins [5][6][7] in body and caudal fin (BCF) propulsion and ribbon fins [8][9][10] in median and paired fin (MPF) propulsion. As the most conspicuous appendage of the fish's body, the caudal fin has also been studied extensively [11][12][13][14][15].…”