4S vs 5S

Discussion in 'Cinestar 8' started by William Johnston, Oct 25, 2012.

  1. William Johnston

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    Actually, and I have a lot of experience with this, the flight controller is quite good about bringing the C8 down without smashing anything. The main problem is if you have altitude hold on. In which case some ESCs want to go up while others want to go down. They compromise and go sideways (my arboreal adventure).
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I agree.

    What do you think the CPU is? It says "ARM STR910" (at least I think it's 0) "44X6" and other letters and numbers?
    I thought they were using Atmega 1284P, but that might be just the FC board (and I don't have either in front of me right now).

    Andy.
     
  3. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Oh. Now that's a definite "feechure."

    Andy
     
  4. William Johnston

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  5. William Johnston

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    The chip is an ARM9 series. It's kind of dated. All of STMicroelectornics current microcontrollers are ARM Cortex-M series.
     
  6. William Johnston

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    I couldn't help but think that if someone is having thermal problems maybe what he should do is try a 3S battery. On the bench, I ran the test for the 3S voltage range (9V to 12.6V) while trying to maintain the same rotor speed of 2700 RPM.

    At 9.0 volts with a motor test value of 117, a motor pulls 3.42 amps and rotates at 2722 RPM consuming 30.78 watts.
    At 12.6 volts with a motor test value of 77, a motor pulls 2.58 amps and rotates at 2690 RPM consuming 32.5 watts.

    So a 3S battery consumes less power than a 4S battery to generate the same motor speed, as expected, and so the ESC won't be as hot. However, the battery may not generate enough power to carry much of a load.
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Was that with a prop on the motor, William, or "no load?"

    Thanks
    Andy.
     
  8. William Johnston

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    With propeller. CS8 tied to the bench.
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Figured as much -- I've got a good sense of your mechanical sophistication!:)

    I was wondering about building a test bench that would also permit thrust measurements -- or am I ploughing old ground and you've already done this?

    Andy.
     
  10. William Johnston

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    I have thought about, but haven't done it. You could use three of these:
    http://www.amazon.com/Tubular-Spring-Scales-grams-Newtons/dp/B004MIH3TM
    one attached to each leg and the bench.
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks!

    I tend to use the stuff from vernier.com -- it's not intended to be research lab grade, but it's extremely good for the kinds of things that I do and I can record the results in real time and display the results graphically.

    Andy.
     
  12. Joe Azzarelli

    Joe Azzarelli Active Member

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    andy,
    interesting url link to vernier.com. ;)
     
  13. William Johnston

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    I suppose the expensive electronic ones would work too.

    It would probably easier to build a rig to test just one engine. However, the airflow over the frame of the CS might affect your actual thrust, so you might not be able to apply the number directly to the CS. Still, it would work fine for finding the best propeller and battery combinations.
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yeah, I know Dave and Christine Vernier personally, and, as I say, if you need to do things like battery life measurement their equipment makes it very easy. I'm also going to use their kit to do some vibration analysis on a C8 frameset that oscillates in flight (without a gimbal) so that I can better understand what's going on -- and thereby how to fix it.

    Andy.
     

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