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scientific way to test props

Discussion in 'General Discussion' started by p fandango, Jul 6, 2016.

  1. p fandango

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    i was thinking of an accurate way to test which props give the most thrust. I was thinking of suitcase scales, anchored down & attached to the bottom of the Phantom. Full throttle in ATTI should give the thrust force kg/lb if i'm correct

    what do people think
     
  2. N017RW

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    For a given RPM and diameter more pitch equal more thrust.

    But what is the effect on motor load, temp, braking (if so equipped), and most importantly efficiency?

    Thrust is only one parameter in design.
     
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  3. tcope

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    N0 is correct. I'd say a hover test would be the most accurate... which has already been done.
     
  4. p fandango

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    i'm experimenting with the cheap triple blade props, & on my lightweight project my main concern is just to get as must speed out of it as possible
     
  5. p fandango

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    in hover wouldn't the Phantom reduce the motors RPM to maintain the same altitude if a prop was giving more thrust

    my thinking that with full rpm in ATTI the Phantom will always be doing the same, no matter what props were on. So the more force applied to the scales means more thrust from the props
     
  6. tcope

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    Yes.... and reduced motor RPM would result in less power and longer flight.
     
  7. N017RW

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    There's a lot of good reading available on the design criterion for MRs.
    Tilt (pitch, roll) is the vectoring of thrust to create forward (horizontal) movement.

    But then gravity, drag, and aero forces created by a tilted shell (if equipped) and other frame parts reduce the amount of thrust which can be vectored so as to not lose altitude. Thus all these (and more) limit tilt and thus your top speed.

    I'm no aero engineer but you should research this a bit as matching props to available power is the key to maximize performance.
     
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  8. p fandango

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    i'm not interested in efficiency, the aim of the test is to see which prop gives most thrust ie speed. Being lightweight it already gets plenty of air time, now i want to maximize its speed

    i've seen plenty of people "claiming" what props work & which don't, i want to accurately test them to see which are best for my aims
     
  9. BigAl07

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    I'm curious to see how these "Scientific" tests turn out.

    Keep in mind that we're not just dealing with mechanical systems with this particular aircraft. It's a "Tuned" system and by tuned we're talking motors, props, battery and ESC (software) all designed/engineered to perform in a specific way. To be honest this is a "softened" system optimized for aerial photography and as such the Flight Controller is expecting certain flight sensors to be reporting in a narrow "normal" area of parameters. The system is potentially going to "adjust" to keep things soft and normal per the FC. If you could re-tune the FC to allow other parameters you might be a lot more productive.

    Of course all of what I'm saying is a mere hunch at best.
     
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  10. tcope

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    The props are such a small factor in this that they don't matter enough as you vary from the OEM props. Tilt and power of the motors account for such a large part of speed that any very slight change in prop is not going to make a difference. I'm sure DJI tried tons of different pitched props and that formulas already exist to follow.

    If you want speed you probably should not have bought a drone known as a camera platform.
     
  11. p fandango

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    how can props be a small factor, its like saying the wheels aren't important on a car. I've got 9443's, 9450's & DJI carbons so know the can make a big difference to speed/responsiveness. This is the exact reason i want to do some proper tests & get some numbers, not just guess work

    i've already removed everything i can, & i'm not going to spend £100 on replacement motors for a mess about drone
     
  12. tcope

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    If that was all that I said, perhaps. To use your example it would be like the same size tire made by Firestone or Goodyear and we are looking at gas mileage. There won't be enough of a difference as both are very good at what they do and any differences are very small when it comes to mileage change.


    What difference do these make? If you have them all and know there is a difference then should you not also already know what those differences are?
     
  13. p fandango

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    i've got a pair of digital suitcase/fishing scales coming which can measure upto 50kg so i'll let see what happens

    hopefully, by doing the test in ATTI it'll minimize how much it interferes & the Phantom will do the same thing everytime

    i totally agree, the Phantom really isn't the best platform to start with for speed/messing about. But i've already got one kitted out with gimbal/fpv, & got several batteries/sets of props so why change to a different format

    theirs a lot of hunch's going on, but nothing much to back up whats being said ;)
     
  14. N017RW

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    The props are effectively Stalled or max slip when the motor is 100% and the 'platform' is not moving (0%).

    Just be realistic with your 'findings'.
     
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  15. p fandango

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    at the end of the day its a £3 set of scales & a tied down Phantom. But with data from the Flytrex, & trying all the different props during the same flying session the varying wind etc doesn't give an equal comparison. Especially when you can feel its quick, but the telemetry says your not even close to your top speed

    i'm trying to get over 50mph (which some people have managed easily), but currently my best is 46.68mph & that was done with the fully loaded Phantom. Lightweight & the different props i was expecting to top it easily, so i want to do some tests in "controlled" conditions & see what they are doing
     
  16. N017RW

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    Hey I'm sorry if I appeared over critical. Look forward to your reports.