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8 Platform one February/March 2017 | Unmanned Systems Technology Energy systems for AUVs have taken a step forward with the release of the results of tank testing of a gyroscopic system that turns wave energy into electrical power (writes Peter Donaldson). Dr Nicholas Townsend at the University of Southampton is developing a system based on control moment gyroscope (CMG) principles, which are commonly used for attitude control in satellites. The study is funded by the UK Defence Science and Technology Laboratory through the Centre for Defence Enterprise. The torpedo-style AUV prototype was tested with regular waves at zero speed in a towing tank, the 10 cm waves producing a maximum vehicle pitch response of 7.5 º and the CMG generator harvesting 0.05-0.6 Wh/h, with a maximum recorded peak power of 8 W. CMGs can be very power-efficient, as large ones of about 100 kg and drawing a few hundred Watts have generated thousands of Newton metres of torque. The CMG-based generator uses the gyroscopic response of an electrically powered gimballed flywheel inside the AUV hull to generate energy from wave- induced pitching and rolling motions. The flywheel’s reaction to input torque provides a larger output torque at right angles to the input torque axis and the spin axis. The vehicle’s motion provides input torque, while the spin axis drives a generator. Dr Townsend emphasised that the mechanism is contained entirely inside the AUV with no need for external appendages, which would induce drag, and said it promises to extend AUV mission times indefinitely and reduce support vessel times for recharging and redeployment. The greatest power was generated by waves that excited the vehicle’s natural resonant frequency, of about 0.7 Hz, but tails off as frequency increases, typically in a non-linear manner, while higher spin rates and larger wave amplitudes yielded greater power. These results proved that it can harvest energy, Dr Townsend said, but in the test conditions it did not achieve a net energy gain. However, in real-world conditions it has the potential to provide additional power for payloads or specific systems. Gyro-based power source Underwater vehicles A gyroscope has been used for the first time to capture the energy of waves to power an autonomous underwater vehicle