Anybody used the new APC Multirotor props?

Discussion in 'Cinestar Misc' started by Matt Barker, Jul 22, 2013.

  1. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I just did a scatter plot of Thrust compared with Watts. It's below. I need to figure out why there is so much variation in the wattage data -- the problem is that I'm having to sample the data at 1,000 samples/second to get the Photogate/RPM data, but I think that's causing issues with reading the current (via a Hall effect device that converts the current to a voltage -- and there seems to be a lot of jitter in the Amps data -- and that's, or course, being used for the Wattage calculation).

    Reading between the lines -- well, dots, actually, it seems that the APC MR's might get more thrust per Watt than the regular APC...with the Xoar's somewhere in between.

    Andy

    Thrust cf Watts APC, APC MR, Xoar 1-03 2013-08-24.png
     
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  2. Niels Johnson-Laird

    Niels Johnson-Laird New Member

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    Andy, think we need to start using the power of Statistics. ;)
     
  3. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I agree. What are you doing this evening? ;)
    Actually, I need to shield the Hall effect sensor and see if I can reduce the sampling rate (as well as using stats).

    Andy.
     
  4. Gary Haynes

    Gary Haynes Administrator
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    Totally agree with Steve on the thrust vs amps issue. Actually I like amps not watts since the voltage varies during the life of the flight. Mario's testing has always been interesting since you can look at his scale and power meter and simply stop the video where you typically see your power. That's why I always look at the 10amp spot. Close to our typical power draw and to my mind gives an apples to apples comparison of a given prop.
     
  5. Niels Johnson-Laird

    Niels Johnson-Laird New Member

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    Apart from having dinner with you guv'ner, not much. Sounds like we need to burn some motors and break some props this evening! ;)
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Gary: Can you clarify your Amps/Watts comment, please? Normally one uses Watts precisely because the voltage will indeed vary and thus as the voltage drops, the current has to increase to accomplish the same amount of "work" (that is thrust) to keep the aircraft airborne. Given Watts = Volts x Amps, as the voltage drops the current will increase, but the Watts remain the same.

    That's why I'm left with that feeling that I'm missing what you're saying?

    Perhaps I should have pointed out that the graph showing Watts was created using a DC stabilized/regulated bench supply set to 16.0 volts?

    Andy.
     
  7. Gary Haynes

    Gary Haynes Administrator
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    Andy doesn't the MK screen show only amperage draw and mah used? I haven't looked at a GPX file in awhile but don't remember anything in watts. Elsewhere, like the specs on the TMotor site, are all given in amps for a voltage. For consistency from other sources wouldn't amps vs thrust be a more consistent of depiction?
     
  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I think you're right about MK Tool, but measuring a motor's efficiency in terms of electrical power input to the motor cf. thrust out is best measured in Watts because you don't know what the voltage is that is giving rise to the current draw in Amps.

    Of course, in this case, I'm trying to provide a measure of the efficiency of the electrical motor (which is a constant for these three tests) and different props.

    For example, see the following link and note the Electrical Motor Efficiency -- in this case, of course, I'm taking it one stage further and I've already converted the power output Kilograms of lifting force, but note the Pin value.

    http://www.engineeringtoolbox.com/electrical-motor-efficiency-d_655.html

    I'm ultimately hoping that I'll test other motors and props and try and understand which are the most efficient -- as well as which are the most responsive.

    I should also give acknowledgement to Old Man Mike, on rcgroups.
    http://www.rcgroups.com/forums/showthread.php?t=1006721

    It was from him that I got the idea to try these tests. Note also that he expresses efficiency in a unit of Watts/oz at maximum Thrust.
    However, I've got no axe to grind -- if folks would rather see Thrust cf. Amps, I can do that without any problem.

    Andy.
     
  9. Gary Haynes

    Gary Haynes Administrator
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  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks. I had see some of those videos but didn't realize they were all conveniently accessible. Mario's work is great. I just wanted to plot out some graphs so I could see at a glance which props might give the most thrust from idle RPM to leap-to-the-stratosphere power.

    I was presuming that the Xoar's would provide the most thrust compared with RPM so, as I say, I was bit taken aback that doesn't appear to be the case. I'll be repeating the entire cycle of tests this week just to verify the data.

    Once I've verified the data from the test rig, I'd be happy to test other motors and props if people are curious about them.

    Andy.
     
  11. Steve Maller

    Steve Maller UAV Grief Counselor

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    I suspect there's a wealth of data there...it's just a matter of lining up all the numbers in a meaningful way. I appreciate the hard work, Andy.
     
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  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I agree -- too much data, too little time! :).
    I'm going to start by re-calibrating all the sensors, as well as getting cleaner data without any outliers (I hate outliers!).
    I also want to do some "sensitivity testing" -- that is waggling the throttle up and down at approximately hover power settings to see how quickly the props/thrust changes. I'd like to get an objective test of at least these the APC, APC MR, and Xoar just so we have some objective data to base our buying and flying decisions on.

    Andy.
     
  13. Steve Maller

    Steve Maller UAV Grief Counselor

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    (nods head, pretending to keep up with superior intellect)
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    You wouldn't write that if you saw the way I fly.... :)
     
  15. Sebastian Meredith

    Sebastian Meredith Active Member

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    My brain aches reading some of the discussions on these forums ... But I find myself coming back for more ... I must be a sucker for intellectual headaches. Great work guys! Please continue delivering the pain :)
     
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  16. Steve Maller

    Steve Maller UAV Grief Counselor

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    I was commenting on your mathematical prowess, which is several neural zip codes away from your vision, dexterity, and equilibrium centers. :D
     
  17. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Aha. As in, there are 10 kinds of people. Those who understand binary and those who don't. Got it.
    There are parts of my brain that don't seem to have zip codes....well, if they do, there's not much zip....

    Sebastian:
    For the headache: Red wine. :) Or Guinness.
     
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  18. Sebastian Meredith

    Sebastian Meredith Active Member

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    [quote="For the headache: Red wine. :) Or Guinness.[/quote]


    Andy .... I think I'll start with the Guinness and finish it off with a fine Red. :confused:
     
  19. Steve Maller

    Steve Maller UAV Grief Counselor

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    That sounds like a recipe for a headache right there.o_O
     
  20. Shaun Stanton

    Shaun Stanton Active Member

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    Andy

    If I could get the raw data I could do a regression and statistical manipulations to see if I can find correlative terms in the power scatter plot.

    Also, you know it would be cool if you could do that same test with coaxial motors. I have been curious to see what the thrust differences in

    1. Identical Diameter/Identical Pitch top and bottom
    2. Identical Diameter with a coarser pitch on top then the bottom
    3. Large diameter on top small diameter on the bottom same pitch.
    4. Large Diameter prop coarse pitch on top/ small diameter prop shallow pitch.

    It would be interesting to dispell all of the myths rumors conjecture with the coaxial configurations.
     

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