Biorobotics Laboratory BioRob

BoxyBotII - Project Goals

Author: Benjamin Fankhauser, Assistants: A.Crespi, M.Perez, Contact:

This project aimed at designing a new version of the BoxyBot fish robot developped at the BIRG.

It included among others:
  • Programmation and Control
  • Fin Design and Testing
  • Simulation

BoxyBotII - Programmation and Control

The Command of the BoxyBot was done using a Central Pattern Generator (CPG). This meant implementing a system of four coupled amplitude-controlled phase oscillators.

The CPG allowed us to change amplitude, frequency and offset of every articulation online and would at the same time guarantee a smooth change.

The position of the robot could be aquired by two cameras placed above the pool.

The control was done by means of a proportional controller in order to make the robot follow a straight line.

BoxBotII - Fin Design and Testing

Influence of Resonance Frequency

To design fins that efficiently made the robot swim fast, we wanted to show the influence of the resonance frequency fR on the speed of the robot. As the graph shows, the fin's resonance frequency (i.e. maximal amlitdue) is at 0.7 Hz.

At the same time we can observe that the speed increases less for higher frequencies.

Efficiency Estimation

Efficiency estimation measures using the Strouhal number proofed that swimming at the resonance frequency of the fin is very efficient.

Influence of Excitation Amplitude and Heigth of Fin

We could show that higher excitation amplitude resulted in higher speed.

Caudal and Pectoral Fins

It could be shown that the movement of caudal and pectoral fins is interfering and movement of the two types of fins at the same time results in slower speed, than using only the caudal fin (cf. video).

BoxyBotII - Simulation


Fin Amplitude

It could be shown that the results for the amplitude of the fin were comparable to reality. The graph shows the measured and simulated amplitude of a caudal fin of 95 x 60 mm, for respectively 40°, 60° and 80° excitation amplitude. The black lines show the amplitude of  rigid fin of same size.