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Weight vs RPM: Characterization and Comparison of MPP driven DJI 8331 propellers vs 3 others

Theo111103

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As promised quite a while ago.

(assuming all datapoints are correct )

When taken a close look at the differences it clearly shows where the props would find their applications. The 3blade Carbon props give high-wind alarms for a reason: RPM's are low from front to back of their Characteristics. The material of the cheap chinese copies of the DJI 8331 stealth props cause them to bend at higher forces causing the respond to that being extreme high rpm's due to less and less lift. MAS props are a bit more rigid and show slightly lower rpm compared to the DJI 8331 originals. All with all an interesting comparison.

An interesting find is that the spread between Front motor RPM ( RPM_F ) and rear motor RPM ( RPM_B ) vary per propeller type and never show overlap. the most significant delta between Front and Back RPM is found on the cheap flexible chinese copy props, increasing almost exponentially at elevated Weight/RPM .

All possible variables that contribute to weight-changes ( Load ) have been defined as can be seen in the upper left corner of each sheet. The last sheet is just a combination of averaged data, extracted from the previous 4 to enable a quick comparison.

Any basic units like Current and Voltages were deliberately decoupled from the equation to keep things more general:
some tend to tune or tweak the driver responses like min/max currents or the PID response of their bird's motor drivers hence making this fit for general interpretation. The MPP is box-stock with the latest FW installed.

Looking forward to feedback or findings w r to the above characteristics or personal experiences.

T

Legenda:

RPM has been measured per Stroboscope.
RPM = Revolutions Per Minutes
RPM_F = RPM Front Propellers
RPM_B = RPM Back Propellers
RPM_AV= Averaged ((Front+Back)/2)
RPM_RC= RPM as read on Remote Control

Weight in Grams, added to COG of Craft.

8612034C-1D3B-49B8-BDCF-5D29CA3EAAD6.jpeg32DD90D7-B2FE-4337-A6AF-30FAC0BC040A.jpegD67B07E3-7F37-46E0-8EAD-DD786B6D20A4.jpeg705D802B-ACC5-4966-ABFF-5CF1C7E0ED0C.jpeg8B5F3B20-92E6-4020-AFF6-A035281CEC45.jpeg
 
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TexasFlytography

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Incredible work here. Very very well done. So in your opinion, the heavier loads are handled better by the stock props? Or the
MAS?
 

Theo111103

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Incredible work here. Very very well done. So in your opinion, the heavier loads are handled better by the stock props? Or the
MAS?
@TexasFlytography : Thanks!

Your question:

That would vary per application: a distinct difference between the 8331 and the MAS Stealth can be found in the delta in rpm and the more"flat" graph the MAS shows while processing heavier load. To my opinion this is due to the material and the shape of the blades.

One of our fellow pilots made a very valid remark after i posted this: what would be interesting is this test with one more Datapoint added per weight being: Powerconsumption ( Watts ). I am preparing to go through the same tests again including that Unit for completion of fingerprinting the various propellers.

To get back to your question: when only taking in account the given data as posted, one could conclude the MAS is more efficient hence should be the propeller of choice for heavy load ( or faster accelleration ) applications.

Without having any data to back-up my assumption, i tend to think that the slower rpm comes at a cost: higher lift usually is generating higher torque on the motor-axis hence currents ( amps ) through the coils of the motors might be higher. since Watts are calculated from W=PxT and P=IxIxR, ( assuming that for a moment the inductive coil of the stator behaves like a linear resistor, just to not get into true rms powercalculations ) there could be a linear proportional relation between the MAS performance and the Powerconsumption.... However: since the rpm is lower at given loads, there might be a crossing in the powerconsumption graphs when compared: here the two props could have the same consumption at a given weight / rpm / torque..... More work to do, will follow!
 
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TexasFlytography

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I have recently stumbled across the ability to alter payload parameters in Assistant(center of gravity adjustment parameters). Have you had any experience with this?
 

MAvic_South_Oz

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Without having any data to back-up my assumption, i tend to think that the slower rpm comes at a cost: higher lift usually is generating higher torque on the motor-axis hence currents ( amps ) through the coils of the motors might be higher.
If it's possible (waypoint mission ?) maybe try and test when static hovering . . . AND another test following a set route in movement, speed same nil wind if possible etc.
It makes sense that a moving drone may use less power, but it might be in the same % loss as hovering, if it turns out the lower rpm does eat into amps used.
 
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surfbird

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8331's are by far most effecient for heavy loaded flight.

Sadly :) I spent a long time testing different props.

When flying steady 8m/s (atti mode) with 600grams extra the 8331 uses 170W and airscrews 180W. Even if the rpm is much lower for the airscrews
8331 even beats the mavic2 props. I going to do another test run with brand new mavic2 props when the wind drops.

You don't get the same results when hovering, it was when I started flying forward I noticed the big difference. So, it's was a huge misstake to do hovering for my measurements.

I havn't tested higher speed though. I'm mostly after long flight times, and slowly forward speed gives me a little bit of over 60min, with 4 dji packs.
 
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Theo111103

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@surfbird:

Thank you Surfbird for your great feedback!
Your work confirms my suspicion that the lower RPM are linked to higher torque hence higher currents and impulse resistance of the coils...hence higher losses at the end... Interesting data!!

All of you Hovering work is not a mistake and certainly not lost, it is a very valuable set of data that completes characterization under various conditions! I would consider that Fundamental data..

Now, throwing in the forward motion
generates a whole set of challenges if one wants to obtain repeateable and
interpreteable data:

Basicly all variables like airpressure, airtemp, windvelocities and variations, altitude etc etc need to get recorded
to satisfy my autistic mind but when great differences are noticed i would go for the Watts ! I use the apple devices, is there a possibility to use the app you pointed to on these?

Looking forward to more from your side!

T
 
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