TWiT Throwback (Audio)

Know How... 139: Making Snow, XYZ 3D Printer, GameBoy Fix, and Thrust Testing

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How to make snow when there isn't any, XYZ 3D Printer, how to fix your GameBoy Screen, thrust testing quadcopter motors, our incredible sun, and more!

Thrust Testing

When we talk about how fast a multi-rotor can go, or how much weight it can carry, or how well it performs, a large part of the conversation is THRUST.

How much thrust can be generated by the craft?

The answer to that question depends on a few things:

  1. The "size" of the motor
  2. The size of the prop
  3. The voltage and discharge of the LiPo battery

    4. Motor:

    Look to Episode 117 of Know How...

    Example:

    • Turnigy 1704-1900Kv Outrunner
    • Emax MT2213 935kv

      • Choosing your Motors:

      This is a problem --- because other than the Kv, motors from different manufacturers don't really report their specs in the same way:

      • Some give you thrust (like the Emax with 850g of thrust)
      • Others just give you the max power (like the 1740, rated for 49 watts)
      • Still others will give you NOTHING

        • If you have a x250, then you're probably going to want a smaller, faster-spinning motor. Larger craft, like a x350, x450 or x525 will need larger motors, with more turns, that spin more slowly, but provide more torque, which you need for the bigger props.

        Props:

        Look to Episode 117 of Know How...

        There are two variables to every propeller: Diameter and Pitch

        • Diameter refers to the length of the propeller from tip to tip
        • Pitch refers to the distance the propeller would travel forward, assuming that it was a perfect medium, in one rotation.
          • The more angled the blade, the higher the pitch.
          • Increasing the DIAMETER of the prop increases your lift capacity (because there's more surface area to the propeller)
          • Increasing the PITCH of the prop increases your top speed (because it increases the distance the prop would move forward in one revolution)
          • Increasing either the Diameter or Pitch of a propeller increases the current draw on your electrical system.

            • Power:

            Look to Episode 118 of Know How...

            Example:

            • Turnigy 1704-1900Kv Outrunner
              • When we give it 11.1 volts, it will turn 21,090 times per minute (1900 X 11.1)
              • Emax MT2213 935kv
                • When we give it 11.1 volts, it will turn 10,378.5 times per minute

                  • So we can give our motor a 3s (11.1 volt) or 4s (14.8 volt) LiPo to change performance AS LONG AS THE ESC/MOTOR SUPPORTS THE HIGHER VOLTAGE!

                  When we run high voltages, we go with smaller props.

                  To measure thrust we need:

                  1. A Thrust measuring device
                    • Turnigy Thrust Stand
                    • An ESC
                    • A servo tester or radio reciever to trigger the ESC

                      • These show notes have been truncated due to length. For the full show notes, visit https://twit.tv/shows/know-how/episodes/139

                      Hosts: Bryan Burnett and Fr. Robert Ballecer, SJ

                      Sponsor:

                      • ifixit.com/twit enter code: KNOWHOW

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