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53 “We have our own machines on which we do all the milling for our prototypes,” he says. “For mass production we contract out the CNC work, but we plan to do all that in-house in future.” The central portion of the airframe, to which Griff refers as a backbone, consists of a narrow aluminium alloy extrusion with four internal cavities. Wider than the backbone, the CNC-machined end pieces provide mountings for the arms that carry the rotors and, in combination with the outer edges of the backbone, form mountings for the detachable battery boxes on either side. The end pieces have vacuum-formed ABS covers. The battery boxes are made of aluminium extrusions, and form part of the structure. The end pieces include shoulders that support the inner portions of the rotor arms. The arms fold on hinge rings close to the body, the forward arms folding toward the rear, and the aft arms folding towards the front. Deploying them involves pulling them out until a spring-loaded lock near the pivot secures them in place. The locking mechanism is a spring-loaded cotter pin that pushes through one of two holes in the inner and outer portions of each arm that lock them in the folded and deployed positions. The four landing gear legs are also CNC-machined aluminium alloy, while the skids attached to them are aluminium extrusions, and can be reconfigured to suit the payload and application. They are also spring-loaded to absorb the shock of heavy landings. Electronic components are mounted in a tray that can be removed as a unit, and protected against vibration using elastomeric mounting blocks. The tray simply pushes into slots machined into the alloy backbone, a solution that makes the UAV easier to assemble and disassemble, and reduces the number of parts by eliminating the need for fasteners such as screws or nuts and bolts. Components in the tray include the autopilot/flight controller, the dual GNSS system that provides heading as well as positioning information, and the radio links. Within the tray, the flight controller is suspended on wires to provide additional protection from vibration. Batteries and motors Griff chose battery power mostly for environmental reasons, along with quietness and low maintenance requirements, selecting industrial- standard 18650 format lithium-ion cells. The cells are from Sony Murata, in Japan, and are integrated into four separate batteries – two for the propulsion system and one each for the control electronics and the payloads, the latter fitting into slots behind the main batteries. The motors are supplied by Rotex Electric, in the Czech Republic, and communicate with the autopilot over a CAN bus system. The motors are Griff 135 | Digest The four-motor version of the Griff 135 with three-bladed folding props. Note the spring-loaded catches that secure the arms in the open and folded positions (Courtesy of Griff Aviation) Unmanned Systems Technology | February/March 2020 When folded, the Griff 135 fits into a single transport case along with its ground control station (Courtesy of Griff Aviation) We have our own machines for all the milling; we contract out the CNC work for mass production, but in future we will do it in-house