To power the drone, household 110VAC will first be stepped up to 240VAC using a 5000W voltage transformer. The transformer will connect to the powered tether cable via a NEMA 6-20 three blade plug. There will be a Mercotac brushless rotary electrical between the plug and the spooled tether to allow rotation between spool and plug without wear of the cabling. The tether will use three 22AWG wire that will be secured with small segments of heat shrink every 6 inches. At the drone, the tether will connect to the TDK-Lambda PFE-1000 AC-DC converter power supply with ring terminals and the tether will be strain relieved to prevent strain on the connection terminals. The power supply will mount with zip ties to the bottom of the drone for convective cooling from an auxiliary fan. The AC-DC converter will connect to the stock drone power input with a short cable and quick disconnect terminals.
tether management System
To manage the tether, a spooling mechanism will be used. Tension will be applied to the tether in order to prevent tangling with the drone’s propellers. To apply the tension, constant force springs will be used. There are three main subassemblies of the tether management system: the spool and gear subassembly, the spring subassembly, and the fixture subassembly. Each of these subassemblies and their interaction with one another is described below in detail. To the right is a rendered image of the entire tethering assembly. As shown in the image, the spool is mounted on a shaft, which transfers through the gears and finally to the springs.
Throughout the process of unreeling, the spool will rotate approximately 110 times, while the springs have a maximum capability to be unwound about 10 times. In order to solve this issue, the rotation of the spool will be geared down by a ratio of 14:1 to assure that the springs will not be over wound. The gear assembly will interface both with the spool and the springs to create a gear reduction between the spool and the springs.
To maintain constant tension without creating too large of a force on the drone, it was determined that 2/3 of a pound would be a large enough force. This force will prevent the tether from getting tangled in the rotors of the drone since the tether will be well maintained and taut.
The fixture subassembly provides support for the gear shafts and the springs. The fixture pieces will be manufactured from plywood, and holes will be laser cut to support the shafts. Wood is used for the prototype because of it's cost and manufacturability. Ball bearings will allow the shafts to spin with little resistance. All shafts will be supported on either side by a fixture so that none are cantilevered.