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Apr 21, 2016, 04:58 PM
Motors and helicopters.
Thread OP
Data

Propeller above or under the quadcopter arm?


I have been doing some tests to compare the effect of installing the prop above or under the quadcopter arms. In theory, the air is moving slower upwind of the prop, as it is pulling air from a larger area.

Air direction

Those tests were also done to compare the two mounting plates offered with the RCbenchmark Series 1520. I wanted to test the worst case scenario, so I tested a small prop with a relatively large prop mount.

Here are the mounts tested:


Equipment:
RCbenchmark Series 1520
Motor DYS R1804-2300kV, 2302kV measured
Lipo 2s 7400 mAh.
Prop Gemfan 6045

Script: Steps - Discrete with the following parameters:

var minVal = 1000; // Min. input value [700us, 2300us]
var maxVal = 2000; // Max. input value [700us, 2300us]
var stepsQty = 10; // Number of steps
var settlingTime = 2; // Settling time before measurement input change [s]
var samplesAvg = 20; // Number of samples to average
var stepsGoDown = true; // If true, the test will step down, if false, the steps will only go up.
var repeat = 1; // Number of times to repeat the same sequence

Relevant cutoff limits:
Voltage (V): 7.0-15.2
Current (A): 0-8
Burst Current (A): 0-10
Thrust (kgf): +- 1

Test Log
Install motor/ESC.
Run Get Number of Poles script. 14 poles and measured 2302kV
Install propeller.
Connect battery.
Room RH% before tests: 32%
Air pressure: 1019hPa (http://www.windfinder.com/forecast/gatineau)
Room temp. : 20 C
Tare.
Run script.

Results:

Click the image for interactive graph.








With the small included plate or the quadcopter arm, there is little difference between pusher and puller. The three different mounting plates showed similar results in pusher. If you have a larger obstacle relative to the propeller size, i'd recommended to run the test or your quad in pusher mode (if you don't mind your quad being a lawnmower too).

Sergey from dronehitech got similar results when testing the large and small plate.

Edit: Raw data: https://docs.google.com/spreadsheets...it?usp=sharing
Edit 2: I forgot to mention, I am one of the designer of the Series 1520.
Last edited by Charles.Blouin; Jan 23, 2019 at 04:17 PM. Reason: Image links were broken
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Apr 22, 2016, 10:17 AM
Registered User
Maxzor's Avatar
Hello, and nice to see such tests!

Could you please provide more details about your setup?
Are the mounting plate vertical (so the prop in "forward flight mode") or horizontal (so the prop being in "standard quadcopter hover mode")?
Did you also, as stated, really unmount and remount the motor from one side to another between pusher and puller tests, or did you just reverse prop rotation?
If the mount was actually horizontal, what height of free airspace was beneath it, and on top of it?

How do you explain the results in relation to the theory you first stated?
Apr 23, 2016, 10:22 AM
Motors and helicopters.
Thread OP
Thanks! The system was clamped down on a table with nothing in front or behind for at least 2m. The prop is in forward flight mode. Other than from potential obstacles such as the floor, the forward flight or quadcopter mode of testing should yield the same results. The test are done in forward flight more mostly for convenience and safety reason: if the prop breaks, the parts will move in the plane of rotation. I find it easier to protect myself during tests with this setup.

The quadcopter arm and mounting plates are pretty much geometrically symmetrical in the plane of rotation or the prop. Consequently, I reversed the prop and motor, which is equivalent to unmounting the motor, as the whole system is geometrically symmetrical.

The air upwind of a prop is slower and comes from a larger area compared to the air downwind:

Source: http://lyle.smu.edu/propulsion/Pages/propeller.htm

Consequently, an obstacle upstream will have less effect on the thrust, because the air moves slower around it, which reduces drag losses. Also, (the area of the obstacle)/(the area from which the air is coming from) is proportionally smaller upwind.

This theory matches the results. With the large mounting plate, the thrust result was almost unaffected in pusher mode, but was slightly affected in puller mode.
Apr 23, 2016, 12:45 PM
Registered User
Maxzor's Avatar
I get it, very interesting.
Racing quadcopters on 5" 4S and 6S can get as high as 30k and 40k RPM, do you plan to include those numbers(converted to your 6" setup)?

I have a semantic question.
Pusher jets in RC are named this way because the motor is placed at the rear of the aicraft considering forward flight representation.
About quadcopters, a hovering aircraft provides vertical thrust to counter gravity. So I represent myself the orientation being bottom to top : a motor being mounted on top of the arm will tend to throw down the air, but pull up the system, whereas a bottom mounted motor will keep throwing down the air but push up the arm. That is my way of thinking, and I consider your way a bit counter-intuitive!

Why this setup is not more popular is the following question I guess.
Apr 23, 2016, 05:34 PM
Registered User
xsergo's Avatar
Charles, as far as I remember the professional Dynamometer Series 1580 has an gyro/acc sensor for measuring vibration, right?

One of the biggest problems with multicopters is vibrations. I suspect using the motor in puller mode to cause less vibrations too. Could you test that too?
Apr 24, 2016, 10:30 AM
Motors and helicopters.
Thread OP
Quote:
Originally Posted by Maxzor
I get it, very interesting.
Racing quadcopters on 5" 4S and 6S can get as high as 30k and 40k RPM, do you plan to include those numbers(converted to your 6" setup)?

I have a semantic question.
Pusher jets in RC are named this way because the motor is placed at the rear of the aicraft considering forward flight representation.
About quadcopters, a hovering aircraft provides vertical thrust to counter gravity. So I represent myself the orientation being bottom to top : a motor being mounted on top of the arm will tend to throw down the air, but pull up the system, whereas a bottom mounted motor will keep throwing down the air but push up the arm. That is my way of thinking, and I consider your way a bit counter-intuitive!

Why this setup is not more popular is the following question I guess.
You are right, I used motor a bit undersized for this prop. I will use a bigger motor next time I test this kind of thing.

What you mentioned in another way of defining it, that is why I included a picture.

Quote:
Charles, as far as I remember the professional Dynamometer Series 1580 has an gyro/acc sensor for measuring vibration, right?

One of the biggest problems with multicopters is vibrations. I suspect using the motor in puller mode to cause less vibrations too. Could you test that too?
I can't promise I will do it this week, but I want to do this test!
Apr 26, 2016, 03:46 PM
Registered User
xsergo's Avatar
Quote:
Originally Posted by Charles.Blouin
I can't promise I will do it this week, but I want to do this test!
Thanks!
May 10, 2020, 08:05 PM
Registered User

Flip a Perpeller


Hi,

I am a newbie and I just got a X500. It came with two CW and two CCW motors. I like to mount them under the wing (upside down ) to push up. It came with Propellers (CW & CCW) that lock for the rotation of the motors. So, I need to FLIP these Propellers over as well when I mount them to the motors, so it would push up when the motors are mounted under the wings (upside down). Is there such Propellers already made to lock and push up for this configuration? How do you refer to them or is there a different way to go about this?

Thank you for your assistance.

Regards,

Givi
Last edited by Givi; May 10, 2020 at 08:11 PM. Reason: speeling
May 14, 2020, 07:24 AM
Registered User
You don't flip the props, just the motors. The props stay facing the same direction, you'll have to reverse rotation direction on the motors.
Jun 04, 2020, 09:21 AM
Are we not men? We are DEVO!
xanuser's Avatar
Data is great.
But the issue is a pusher generally means longer landing gear (more mass) and/or the motors and props closer to grass and debris when taking off and landing. I have a fair amount of iron in my soil here, I like to keep it out of my motors as much as i can.


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