GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.3 GNGTS 2024 On the basis of this new technology we have designed from scratch and realised a fying payload mounted in an aerodynamic “rocket-shape” towed assembly. Our system core is a new optcally pumped micro magnetometer from QSPIN, the Total-Field Magnetometer (QTFM). Along with this sensor the system has GPS positoning system running at 10 Hz, 9- DOF IMU unit for attude and heading reference, barometer and thermometer for indirect absolute alttude measuring, laser altmeter (up to 50 m) for direct terrain clearance (AGL) measure. All of these data are acquired along with milliseconds onboard processor clock for post processing data resync. Data is read from sensors synchronous to the magnetc measure actng as master sync and stored on a local repository. A bi-directonal radio link has also been implemented in order to communicate to a ground based staton through LORA (Long Range) signal modulaton. It ensures radio connectons over long ranges even with very low antenna RF power through the use of a redundant and compressed data modulaton scheme. This is important to maximise efciency with respect to onboard batery weight. The enhanced efciency is however payd on data bandwidth: for our system setup a maximum of about 22 bytes/second are allowed for connecton nominal distances of 5 kilometres and few mW in TX. Over this link a binary compacted subset of survey measurements is transmited to a base staton: the subset ensures the issue of a magnetc data map rendered on a laptop for real tme quality check of survey progression. Even if magnetc data is transmited to the base staton in a simplifed-rounded way for bandwidth optmisaton it can nonetheless act as data backup in the unlikely cases of on-board log failure. It is also possible to remotely control the system through a handshake (ready to send status - acknowledge) protocol to change some survey parameters: measurements frequency (future feature), control of recording status and of recording parameters setup for diferental barometric alttude measurement. Fig. 1 shows the magnetometer rocket-shaped system (bird): all of the electronics are in the nose of the bird running around an arduino-like powerful 32 bit microcontroller. The actual sensor is instead put farthest from the electronics and from the batery in order to minimise unwanted magnetc noise: it is in the bird tail, inside the wooden ailerons holder. Apart from the electronic components, the bird is in fact entrely made of non-magnetc materials and during fight it is towed by the UAV with a 10 metres rope. The system has been conceived to be independent from the AUV host platorm. It is furthermore very light weightng about 1kg, batery included. It is very economical if compared with similar commercial systems. It is low energy consuming: a ~5000 mAh USB power pack gives 2-3 hours of autonomy. The actual implementaton of the system has demonstrated to fy stable in moderate velocites even with some wind conditons. Future improvements foresee the implementaton of an actve stabilisaton system to minimise bird pendulum-like oscillatons for low velocity situatons and/or caused by wind turbulence.