Unmanned Systems Technology 014 | Quantum Tron | Radio links and telemetry | Unmanned Aerial Vehicles | Protonex fuel cell | Ancillary systems | AUVSI 2017 Show report

30 “So you are much quicker in development. It’s perfectly normal; I think it’s human nature,” Seibel says. Operator safety issues also come into play at greater weights, he says, pointing out that a propeller on a 25 kg vehicle can chop off an errant hand, while that of a 5 kg machine would merely draw blood. Finally, a dedicated C2 link whose sole function is to cut all power in an emergency is needed, in case the flight controller does something unexpected, for example. On the subject of crashing, Seibel is quite open – the development programme over the past four years has claimed eight airframes. “Anyone who says they’ve had no crashes just hasn’t tested enough,” he says. However, he emphasises that none of the losses were caused by an autopilot malfunction. “All that work we did with software-in-the-loop and hardware-in- the-loop malfunction testing worked perfectly well,” he says. “Most of what we experienced was mechanical stuff – servos that failed, electric motors that were overheating, human error.” Fully half of the losses were down to human error, he says, citing screws not properly tightened and batteries not fully charged. “For example, one propeller came off because the manufacturer had misinterpreted the number of carbon fibre rovings [fibre bundles] we wanted,” he says. That was easy to diagnose because the blade was missing from the collection of parts they retrieved from the crash site. “We finally found it, and it looked like it had just torn off.” Quantum put big efforts into data recording and analysis during the test programme. Seibel says, “We logged about 350 parameters at a sampling rate of 100 Hz so we could do a proper investigation every time something went wrong. In 100% of the cases we were able to identify the problem.” ESC factors Of the other half of the airframe losses, most were caused by problems related to the motors and ESCs. Twice, Seibel says, the ESCs switched off because they thought they had detected an under-voltage. “So we had to talk to the manufacturer and tell him that no matter what their ESCs do, never turn them off, even if an under-voltage is detected. Let our autopilot decide.” Shutting down to protect itself and the batteries is normal and acceptable behaviour for an ESC in a radio- controlled model motor glider, but pointless in a hovering tiltrotor. Here, a voltage drop might be the normal result of a current spike, itself resulting from the motors’ response to a climb rate command from the autopilot. “The ESC in that particular case switched off because it had measured something wrongly; there’s no guarantee though that the ESC is right. If I am not sure who I can believe, then I don’t want it to turn off, because if the voltage is breaking down, the UAV is going to crash anyway, but let’s not crash it to save an ESC.” To deal with the human factors issue, Quantum now draws on the founders’ military background and implements checklists for everything, in addition to creating a UAV system that can complete its missions autonomously. June/July 2017 | Unmanned Systems Technology The Tron’s nose cone is its primary sensor mount, which can be configured to support multiple cameras for agricultural and geospatial survey missions