A WIRELESS UNDERWATER TORQUE MEASUREMENT SYSTEM FOR SELF-PITCHING PROPELLERS

The even more large diffusion of self-pitching propellers leads to a more accurate analysis of their behaviour in running conditions, to avoid the onset of system instabilities under small deviations around the equilibrium working points. Unfortunately, the real time measurement of physical quantities in propellers' tests is a great challenge because of several intrinsic setups' complications due to submersed and rotating parts, restricted space for sensors and acquisition systems as well as data storage and transmission. In this paper the experimental setup developed to accomplish the WP's for the 7th FP project HYMAR is described. This setup is addressed to measure the torque acting on the blade as a function of pitch angle in particular around the equilibrium points at different speeds. The solution adopted is based on a wireless custom acquisition board placed inside the rotating shaft. The torque is measured using a miniaturized set of strain gages mounted on customized blades' joints. Data storage and transmission tasks have been achieved using an integrated on board memory and a 2.4 GHz transmitter module. This solution, that could appear a little bit strange for an underwater system, has the great advantage that it is possible to send and receive data using a probe containing a common USB Bluetooth adapter. Communication throughout water has been theoretically estimated and experimentally proved to be possible in water only for small distances (10-15 cm), but enough for this setup.