Unmanned Systems Technology 012 | AutoNaut USV | Connectors | Unmanned Ground Vehicles | Cobra Aero A33i | Intel Falcon 8+ UAV | Propellers | CES Show report

64 Digest | Intel Falcon 8+ UAV Each IMU incorporates an accelerometer, a gyroscope, a magnetic compass (or magnetometer) to detect magnetic fields, a barometric pressure sensor to detect altitude, and a Trinity processor board. “We have three of these ‘compute sticks’,” Stumpf explains, “two of which act as redundant hardware to each other, which we call Navigational Processors 1 and 2. The third is principally used for orienting the payload. “All these processors communicate along a high-speed bus to fuse crucial navigation information, and each processor is connected to one comms modem, one motor bus and one power supply. If any of these fail – an IMU, a data port, a modem link and so on – then another ‘chain’ of information can take over, and the UAV will continue to work.” In addition to having a back-up navigational processor, Trinity’s three IMUs incorporate a triple modular redundancy function into their behaviour. This involves three systems each performing an iteration of the same process, after which the result is processed by a majority-voting system to produce a single output, and if any one of the three systems should fail, the other two systems can correct for the discrepancy. Stumpf says, “When you’re using analogue sensors such as an IMU, and you have only two of them, when they give different readings you can’t be quite sure which one is giving the correct value. For example, one gyroscope may state that the UAV is tilted by +20 º to the horizontal, just as the other gives a reading of -20 º , and without aids such as vision or satellite navigation it is difficult to ensure the flight computer’s accuracy. “So, in these sorts of cases you need a triple modular redundancy coupled with a ‘majority voting’ system, so that if one sensor says -20 º and two say +20 º , the CPU accepts the +20 º data input. But if you vote and switch between the different inertial sensors, even with milliseconds of difference, you run into problems when the UAS gets into unstable flight, or gets into pilot-assisted oscillations.” Such problems, as well as noise and offset error, can lead to instances where gyroscope readings might look something like -19 º , -21 º and +19 º . The adaptive software of the Trinity flight controller is programmed to eliminate the clear outlier (+19 º ) and then take an average of the remaining readings to provide as sound a reading as possible from which to base its next manoeuvre. Despite the various navigation redundancies on the Falcon 8+, only one GNSS unit is installed. “The software and architecture support redundant GPS,” Stumpf notes, “but we don’t consider it vital for flight, it’s more for pilot assistance than safety. If you include two GPS units you don’t necessarily improve readings; you just take whichever reading is reporting with sharper accuracy, down to the lowest number of metres.” For increased accuracy, the company has announced support for real-time kinematic processed GNSS for operators seeking to fly a particular route or set of GPS or GLONASS coordinates. Data links The Falcon 8+ uses two comms transceivers for dual redundancy, which transmit through the data link antennas housed in the vehicle’s feet extending from the carbon cross-rod underneath the centre hub, with cabling for control and comms running through to the centre hub, inside which are the transceiver units. Each 100 mW transceiver transmits the same information simultaneously. “If one link fails,” Stumpf says, “the other still transmits 100% of the information. In urban environments, ‘shadowing’ effects can create instances in which one antenna lacks reception, but the other one can be better placed to transmit and receive to and from the Intel Cockpit ground control station.” The data link transmits over the 2.4 GHz wireless band using a proprietary protocol. “It’s an adaptive February/March 2017 | Unmanned Systems Technology The Trinity flight controller’s algorithms allow the Falcon 8+ to compensate for the loss of a working rotor by shutting down its counterpart on the opposing rotor