The team achieved one of our major milestones during testing on the weekend, controlling multiple UAVs through a multi-point comms network.
One of the main challenges for our mission will be establishing reliable communications between our ground station and the retrieval aircraft when it lands at a distance of over 10 km away. To solve this we will keep our support aircraft flying in the air and use this to relay the telemetry from the ground station to the retrieval aircraft on the ground.
On the weekend we successfully demonstrated the relay concept in the field using a 1W 900 Mhz radio link between the ground station and the support aircraft (Ben’s X-UAV Talon), and then relayed the second telemetry link to the retrieval aircraft (Steve’s Crash Test Hobby Reaper) using a 25mW 433 Mhz radio link. Both aircraft were fully controllable in autonomous flight. The retrieval aircraft was flown to a distance of 700m from the support aircraft and still maintained a reliable link.
Ben has done a lot of work developing this comms network, which utilises an IP Bridge over the 900 Mhz radios to send different streams of telemetry and route them where the need to go. A Raspberry Pi was attached to the mast on the ground station and created a local wifi network so that the ground control station laptops could send their telemetry links through the 900 Mhz radio link. A Raspberry Pi in the support aircraft then received those links and routed the telemetry to either the support aircraft’s autopilot, or the 433 Mhz relay link.
Besides allowing us to send two telemetry streams, the IP Bridge also allows us to send imaging data. We were able to stream a first pass low-resolution view of a 3MB image suitable for planning a landing approach, while maintaining a reliable control link to the UAV. For the mission we need to send images back from the target site to find Joe, and identify a suitable landing site. We were originally planning on using a secondary long-range wifi link for the imaging data, however if the IP Bridge over the 900 Mhz radio proves reliable enough this may not be needed which will keep things much simpler.
They day of testing was not without its lessons though. We had two failed take-offs from the Talon due to the heavier payload, and also an eagle attack from which we were lucky to recover the aircraft!
We are very happy to achieve these major milestones. Our focus will be to now continue testing and proving the reliability of the comms network, and continuing to develop our retrieval lander aircraft. Much more testing awaits!