Real world props test...

Attached is some data I collected looking for the best prop for my stuff..

The APC electric are as good as APC slow fly... that surprised me..

3690951003?profile=original

3690951024?profile=original3690950963?profile=original

Eddie Weeks

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  • @Adam: The Korean paper you reference makes the case that the Kov in forward flight has a unique relationship to advance ratio (related to blade pitch).


    @all: The Wright Brothers' first powered airplane had twin propellers.  Isn't it intriguing that more than a century later, we're still investigating how two propellers working together interact with each other?

  • I thought I would post this before I run off for weekend. We just finished testing this morning and I processed all the data this afternoon. See the attached PDF for all of our test data. Cheers!

    Final_Test_Data.pdf

    https://storage.ning.com/topology/rest/1.0/file/get/3692482209?profile=original
  • I don't think overlaping props will work...  One will be CW.. the other CCW.. has to be that way..

    They will cross the same area going the same direction.. adding more swrill to the air...

    Is that Right.. ?

    Eddie

  • Good info guys.

    I just ordered 9 NTM 3536-900 motors.  Hopefully that wasn't a mistake, I see you guys seem to be testing the pancake motors, but when I was looking around, seems like everybody else is using standard profile motors?  I almost went with 2836-750 motors, but a huge goal of this machine is to have enough reserve power to have a good chance of surviving a motor failure while carrying a payload, and I wasn't sure I'd get that with the smaller motors.

    Anyway,  I've been trying to figure out however, which props to use and thus how far to space the arms on the Octo.  

    I'm actually thinking of doing overlapping props, but flipping alternate motors up/down.  I've got a design for the Octo with 12" props and the ideal 20% overlap (as detailed by Brad Hughey).  The idea here, if you aren't aware, is that in theory, having 20-30% overlap can actually increase the thrust vs. a single motor due to some beneficial aerodynamics.

    The diameter with this design works out to about 630mm, so it's a compact Octo, but with lots of power.

    If I wanted to go with 14" props with the same overlap, it would require a diameter of 750mm.  

    And then a "standard" Octo with 12" props would be about 850-950 with 12 or 14" props.

    So the potential is there to benefit with more efficient lift.  And also the compact size is easier to transport.  But I do wonder about stability, if the shorter arms will make it less stable?  There seems to be some trend there, but I don't have the experience to say.

    Anybody have any input?  Wanna guess which props will be better for these motors, 12" or 14"?  

  • All,

    Thanks for reporting this practical data. It seems so much better than reading all the speculation and eCalc. I have to ask if the "black" props you used are the rather flexy thin props like I got from 3DRobotics? Mine were way out of balance and seemed too flexible. I decided to buy a batch of APC 12 x 3.8 and I like them. I felt like the lower pitch would give my 880kv motors a "lower gear" to haul a modest GoPro payload on my 3DR quad. And throttle response has been too sensitive for me. Even the smallest throttle adjustments yield too great an altitude change. I want very stable altitude to match the roll and pitch stability. 

    Your data supports my 12 x 3.8 choice. Yeah! 

  • Here is our calibration data from two calibration runs as well as the raw data from my above post.

    calibration.xlsx

  • Strangely enough we are doing the exact same thing right now. We are finishing up our testing tomorrow of all of our tests. Long story short, we are sweeping through the throttle range of our esc and recording the thrust given off by our motor and the power draw by our esc. Here is our data in the same format that you presented your data with. I am curious as to how you calibrated your thrust readings.3692481600?profile=original

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