Underwater robots conventionally use vision and sonar sensors for perception purposes, but recently bio-inspired sensors that can sense flow have been developed. In literature, flow sensing has been shown to provide useful information about an underwater object and its surroundings. In the light of this, we develop an underwater landmark recognition technique which is based on the extraction and comparison of compact flow features. The proposed features are based on frequency spectrum of a pressure signal acquired by a piezo-resistive sensor. We report experiments in semi-natural (human-made flume with obstacles) and natural (river) underwater conditions where the proposed technique successfully recognizes previously visited locations.

This paper studies the modelling, design and fabrication of a bio-inspired fish-like robot propelled by a compliant body. The key to the design is the use of a single motor to actuate the compliant body and to generate thrust. The robot has the same geometrical properties of a subcarangiform swimmer with the same length. The design is based on rigid head and fin linked together with a compliant body. The flexible part is modelled as a non-uniform cantilever beam actuated by a concentrated moment. The dynamics of the compliant body are studied and a relationship between the applied moment and the resulting motion is derived. A prototype that implements the proposed approach is built. Experiments on the prototype are done to identify the model parameters and to validate the theoretical modelling.

This paper describes a sensing-actuation coupling of a robotic trout that detects changes of the laminar flow speed using an on-board pressure sensor and adjusts its tail-beat frequency for steady swimming. The caudal fin actuator closely mimics the morphology of a real trout, in particular the geometry, stiffness and stiffness distribution of the body and the caudal fin. We hypothesize that the linear relationship between the tail-beat frequency and speed, well-known and proven to hold for all fish studied so far, also holds for an artificial fish. We validate the hypothesis and use the results to derive a linear control law to adjust the tail-beat frequency to the swimming speed. We use an onboard pressure sensor to detect the flow speed and test the actuation in a controlled hydrodynamic environment in a flow pipe.

Within the broader scope of underwater biomimetics, in this paper we address the relevance of factors such as shape and elasticity distribution in the ability of a compliant device to imitate the kinematic behaviour of a fish. We assess the viability of myometry as a tool to determine candidate mechanical parameters without relying solely on analytical models; we show that we can obtain elasticity distributions that are both consistent with previous theoretical investigations and experimentally better adherent to the passive kinematics of a biological embodiment (rainbow trout).