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Tethered Quadcopter Help!

  1. Jan 7, 2013 #1
    I am trying to build a quadcopter that is powered from the ground.

    The quadcopter requires 800-1000 watts when at full power.

    I want to send high voltage DC up the tether so the overall gauge of the wire is smaller, and therefore lightweight.

    Lifting capacity of the quad is 15lbs, so I need to find a cable/wire that is lightweight enough to have a length of around 300ft.

    A high voltage DC-DC converter will be used onboard the quad to step down the voltage to around 22.2v-29.6v




    What voltage and current would I need to send UP the wire to meet the requirements at the quad?

    What kind of wire could handle enough power for the quad to reach 300ft, while staying under 15lbs? Of course the higher the quad, the heavier the wire becomes.


    Pardon my ignorance, just looking to be pointed in the right direction.
     
  2. jcsd
  3. Jan 7, 2013 #2

    berkeman

    User Avatar

    Staff: Mentor

    Welcome to the PF.

    It would be best if you stayed with SELV (safety extra low voltage) on the tether wire -- using higher voltages than that would be pretty unsafe, given the application.

    SELV is <50Vrms or <120Vdc:

    http://en.wikipedia.org/wiki/SELV#Separated_or_safety_extra-low_voltage_.28SELV.29

    Are you going to be using batteries to supply power, or do you have access to an AC Mains connection?

    I'd probably start with looking at speaker wire for the actual cable. It's reasonably flexible, and comes in different wire gauge sizes. You will want to size it so there are only a few volts drop from the source to the copter. Use the 1000W number and the supply voltage to figure out the current with P=VI, and then choose a wire gauge that only drops a few volts in the 300 feet of cable. You get the resistance per foot for the cable from wire tables (easy to find with a google search). Remember that the current goes up and back, so you want only a few volts of drop in the 600 foot round-trip run.
     
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