1001copters.com [benchmark] motor and propeller test

[1001 Copters]

Good morning (or night )

I have started a big measurment campaign about motors and propellers.
Until now there wasn't so much data about configurations on motors and propellers, we can found some tests but with multiples motors and one single prop, or some test with one motor and one prop, some tests with thrust vs intensity (useless see below), ...

My scope is to take one motor and to test several propellers on it with exactly the same conditions.

here is the test bench :

Using charts to show thrust vs intensity is useless: most of the people that are doing motorprop test are using LiPo to power the motor. We all now that the voltage is running low along we use the LiPo the motor need a power (P=UxI) to spin the prop, if the voltage is lowering, the intensity rise so a charts that shows thrust vs intensity means nothing if the power source is a LiPo (of course it's different if the power source is a stabilised power supply)

I use a data logger that record: Intensity, voltage, power, rpm and T°
A balance gives the thrust in gr.

All the test protocol is described here

For now I have tested the AXI 2814/22.
next motor on the bench: MK 3538

I have to publish the summary chart for the AXI but I can say that the best prop regarding efficiency is the 14x5 XOAR, the best one for Vibrations is the triblade 13x6 XOAR followed by the 13x6.5 PRECISION XOAR.
(I have also tested APC, Egraupner and EPP)

All the results for the AXI 2814/22 can be seen here


important note: this bench havn't been designed to record vibrations. Data shown are just indicative. Another test bench will be made to make better vibrations measurments.

 

[jes1111]

Very interesting working - and it shows how good those Xoar props are! But... whilst I agree that current consumption (I assume that's what you mean by intensity) will vary with voltage, Axi quote the maximum capability of their motors in Amps - in this case 25A/20s. According to eCalc, the 13 and 14 inch props are too much for the motor - full throttle will break that limit. I know some people say "well, I'll never use full throttle on my AP ship" but all the best advice I've read is that such an approach is inviting trouble.

 

[1001 Copters]

Hi Jes1111,

sorry for my bad english, yes I mean current instead of "intensity"

if you look at my charts, you will see that for a 750gr lift with the AXI and a 14x5 XOAR, you're using nearly 90W. If you are on low voltage on your LiPo, the voltage will be around 13.2V 90/13.2=6.8A

So in hoovering : no problem.
One value commonly used to determine the power needed to have a good behavior of your aircraft is to use 2.5 time the weight of your Mk.
let's see that closely:
0.75kg x 6 = 4.5Kg.
4.5kgX2.5= 11.25kg
11.25/6=1.875 kg.
You must be able to handle 1.87 kg per motors on an hexa according to the 2.5 factor.
It's nearly 325W 325/13.2=24.62A

To have a good behavior of your aircraft your motor must handle 24.6A, that exactly the limits of the AXI 2814/22 according to manufacturer.
If you push the gas stick to the maximum for 20 sec you will be far far away from the legal height limit I think

Before having problems with the motor I think you will have problems depending on the prop you are using.
APC's manufacturer recommand a speed limit for his prop. On our mk, we broke this limit (I will publish modified curves that include this manufacturer recommendation) evry day.
so ok, there is no report of APC broke during flight actually but heavy lift machine is something relatively new (6/8 months).
For my part, when I build a machine for a customer, I don't play with safety. Manufacturer recommend no to go up to 5600 rpm ? ok I use other props.

Xoar's prop are given for 10 000 rpm max, so my choice is made

 

[jes1111]

Current consumption at full throttle is determined entirely by the prop, i.e. it is independent of the weight of the craft. The only effect that weight will have is to determine what acceleration you'll experience (i.e. the amount by which thrust produced exceeds the weight). (Try it on eCalc )

 

[1001 Copters]

That's right, it's good to know the limit of your machine.

Mktools allows lots of parameter, you can limit the gas course in order to have to maximum current admissible in your motor

 

[Bartman]

Cedric,
Looking at thrust vs. power is it correct that the 2-blade Xoar 12x5 makes the same thrust as the 3-blade 13x6 Xoar while using the same amount of power? That's doesn't seem like an intuitive outcome from your testing.

 

[1001 Copters]

Hi bart,

the 12x5 XOAR needs 100W and the triblade needs 95W. But your remark is true about the efficiency of the triblade. I was expecting other results about this tri blade but there are other important point to notice about this tri blade:
the RPM is only 3975, the only prop that have a lower speed is the APC 14x4.7. Why this information is important ?
evrybody knows the famous formula Ec=1/2 mv². If your lower the speed, you will produce less energy. less cinetical energy produced means less amplitude vibrations

There is another clue that need to be investigated: does the motor has enought power to spin the triblade ?
I have an AXI 2820/14 to test: we will see with this one if the results are different

And finally there is another another point to investigate
take a two blade, place it on your motor and feel the air behind the prop. You will feel that it comes with impacts, it's not very fluid.
Make the same with a tri blade: the air flush is smoother.
What does that mean ?
It means that the arm under the motor is hit by air impacts.

My feeling is that with a tri blade you have less vibrations than with a two blade. My next bench will probably shows that
If you have the same efficiency or even 10% less but really lower vibration,s what would you choose if you want to make videos ?


note: this analysis is an exclusivity for your board

 

[Bartman]

Cedric,
I'm running the Avroto motors so I'd guess the performance differences won't be too far off your initial Axi tests. If I'm reading this correctly, I can go from 12x5 2 blade props to 12 5 or 6 three blade props and not suffer much of a battery life penalty. Even 11x6 three blades should be an even swap with everything except vibrations which will be an improvement?
Great information and thanks a lot for posting it. Maybe I can ask Jim at MontoRC to send you an Avroto motor to put to the test. It's a popular motor over here in the US.
Bart

 

[1001 Copters]

It should be very nice of you
I have had some demand to test the Avroto motors, it's a new interesting value on the multirotor universe.

I have made these tests to have the correct information, I can't say if one other triblade would have the same efficiency. What I have ever heard is that the three blade have less efficiency than the two blades. this one seems to have the same efficiency than 2 blades, perhaps it' an exeption ^^

ps: I give you my personnal data by PM.

 

[jes1111]

The other difference between a 3-bladed and a 2-bladed prop will be the frequency of the vibration produced - the 3-blade will produce a higher frequency vibration - effectively easier to isolate.

 

[Bartman]

got the PM Cedric, we'll see what happens with my request.

I've considered running four 2 blade props and four three blade props together on my okto to see if the complexity of the two modes of vibration can actually lessen the intensity of either mode. another of my crazy ideas.
just completed an extensive rebuild of my camera mount so maybe i'll be able to test by monday. all very interesting.

 

[BorisS]

Hi Cedric,

really looking forward to your test with the 2820/14 axis. Will they be next or are they just next on the sub menu on your page ?

Thanks

Boris

 

[1001 Copters]

Hi jes,

effectively the 2820/14 are the next one I wil test because I have a personnal interest in
I'm building a quad with 2820/14 and triblade 13x6 so I want to know what's inside the beast

The test will be made during august? Why ? first of all, I leave in holidays for 3 weeks in Sardaigna and secondly I need to have changes in the protocol. I want to collect more data and this need to modify the software I use.
i will try to motivate the conceptor of the soft...

 

[BorisS]

Hi Cedric,

thanks for the answer. I have them on my new hexa and cant decide which props i should use. Looking forward to your results.

Boris

 

[krleas]

@ Boris
APC 14 x 4.7

 

[1001 Copters]

@Boris: If you plan to make videos, Use the XOAR, it's already pre balanced.
The balancing out of the plastic bag i far far better than with APC.
try it

 

[Wayne Jones]

1001,

Thanks for doing the testing. I am currently using APC 14x4.7 props on my cinema series hexa. Do you know if Xoar has counter rotating 3 blade props? If so I think I will buy some and compare video. My motors are Axi 2820/14. I can hard mount my gopro to get the most vibrations possible for comparison

 

[1001 Copters]

Hi Wayne,

Yes XOAR is selling 3 baldes prop in CW and CCW the cost is very very heavy: 3 to 4 times the cost of a two balde prop (there much more work on a 3 baldes).
I'm building a quad with these props to make some live test too.

I will soon propose these three balde in my shop (within 2 months) but before I must show that the interest is a major regarding two baldes because if the vibrations aren't much lowered as expected it won't be interesting.

 

[holco]

Any News regarding the Avroto motors with the Xoar props?

I am one click away from ordering six Xoar props for my Flexacopter but need to know what sise to choose!!

 

[1001 Copters]

I'm sorry, I'm working on my CNC actually.
i will do the test later :/

By the way, Monto Rc should have sent me one motor to test but I have never received it :/