Changing props vs amp draw

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  • antslake
    RC nut
    • Nov 2010
    • 214
    #1

    Changing props vs amp draw

    So there is a chart for figuring out theoretical speeds of props in their respective hulls. But is there a way to calculate (approx.) how much amps will go up or down on a prop change?

    example, I am running a x437/3 on 4S@70amps, and want to go up to a v940/3. Is there a way to calculate approx what the amps would be?
    Tags: None
    • noodler
      Member
      • Aug 2010
      • 33
      #2
      Have you tried the FE calculator? Do a search and download it. It has some good info to get you close to what you are looking for.

        Comment

        • sailr
          Fast Electric Addict!
          • Nov 2007
          • 6927
          #3
          That is a hell of a jump from 436 to 940! My guess would be a 940/3 is going to draw a lot more than 70A
          Mini Cat Racing USA
          www.minicatracingusa.com

            Comment

            • antslake
              RC nut
              • Nov 2010
              • 214
              #4
              Originally posted by sailr
              That is a hell of a jump from 436 to 940! My guess would be a 940/3 is going to draw a lot more than 70A
              Oh yea for sure. I was just giving a hypothetical example. (well not really). In my King of Shaves boat, I have been messing around with different number of cells. The boat can run from 3S to 6S. One automatically assumes 6S is the fastest. But I think there are a few factors that come into play. One of them being 6S on a 2000kv motor is a lot of rpm's. At what point do friction losses become to great? Doesn't friction lose (in the drive line) go up exponentially? Not to mention the extra weight in the boat.

              So I am experimenting with a few things. Trying to get the most speed out of each #of cells, while trying to stay within the recommended amps of the boat (60).

              Example: my 437/3 runs 70 amps on 4S and about 38mph. The same prop on 3S only goes about 24mph, and draws just under 50amps. So what prop would I run to get the 3S setup closer to the 4S setup? Then what prop could I run on 6S? That same 437/3 on 6S I think draws over 100amps. On 5S it drew 88amps. Way over the recommended capacity of the boat.

              I mean understand how it all works, just that buying props and sharpening them is very time consuming, and any info towards picking the right one will help. I started another thread on all my testing with the props. Right now, I am waiting for another flex cable, and it looks like the lake is about to freeze, so I will be concentrating on ice racing for the next few months.

                Comment

                • antslake
                  RC nut
                  • Nov 2010
                  • 214
                  #5
                  Originally posted by noodler
                  Have you tried the FE calculator? Do a search and download it. It has some good info to get you close to what you are looking for.
                  Right before I made this thread, I had read the one about FE calc. I wondered if that would answer my question, I will check it out.

                    Comment

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