Efficiency of the original DJI Mini 2 propeller

[Dynamicus]

Test conditions: voltage for ESC power supply is 8.8 V, altitude 230 m, air temperature 23 °C
(Note: The efficiency measurement of each propeller affects the efficiency of the motor and ESC used. The measurement of the efficiency of very small propellers from DJI drones is affected by air temperature, air pressure and humidity, which are most noticeable when the motors start to spin up.)

The graph shows that if the propeller reaches 9639 rpm, it has an efficiency of about 8% (8.2% to be exact). However, as the speed increases further, the efficiency drops further, so further increases in speed are no longer relevant to the graph. These speeds produce a thrust of about 64 g and the four propellers thus produce a total thrust of 256 g. And since the weight of the drone is 249 g, at 9639 rpm it starts to climb upwards.

But the propeller efficiency of 8.2% achieved is not dazzling, creating room for significant propeller innovation. The achieved efficiency of each propeller has a major impact on battery life. Instead of increasing battery life, reducing noise or increasing thrust may be chosen, but this requires additional modification of the propeller shape.

The achieved propeller efficiency should be of particular interest to propeller designers and manufacturers. For the average drone owner, efficiency may only be important when he or she starts to wonder how battery life could be extended, drone noise reduced, some record (maximum altitude, etc.) achieved. This can primarily only be achieved by replacing the propellers with propellers with significantly better characteristics.

Maybe some propeller manufacturer (from the EU, USA, Australia, etc.) will take notice of this chart (or all the charts I posted) and show interest in producing the first truly high performance propellers for the most popular drones. I can provide such a manufacturer with more of my aerodynamics knowledge to make the upgraded propellers the absolute aerodynamic cutting edge.

If anyone has one unused original DJI drone propeller at home that I have not yet subjected to efficiency measurements, they can send me the propeller - the propeller may be used, slightly worn, etc. It will contribute to a good cause.

 

[Hooch33]

That would be awesome if they did, maybe a 5 blade race prop to get this thing to pick up some speed, I wanna go fast Ricky Bobby

 

[zenonn]

Well done!
However, it's not clear (to me) at what RPMs the thrust is sufficient to break even with the weight.
9639rpm or for every one rpm in the measuring range.

 

[Dynamicus]

That would be awesome if they did, maybe a 5 blade race prop to get this thing to pick up some speed, I wanna go fast Ricky Bobby

I don't think it's possible to significantly accelerate a drone in level flight (for example in a tailwind). The maximum speed of the drone is probably limited by software. This has already been addressed somewhere on the forum. Increasing the speed would probably be possible with a DJI FPV drone etc.

It is possible to upgrade the propellers just to increase battery life, reduce noise or increase thrust (or a little of each). Increasing thrust will allow for increased speed when flying upwind, for example.

 

[Dynamicus]

However, it's not clear (to me) at what RPMs the thrust is sufficient to break even with the weight.

I'm afraid I don't know exactly what you mean. I'll try to explain it in another way: If you start the engines, they reach about 4000 rpm. If you then start to increase the speed of the motors, and each motor reaches about 9640 rpm, the drone will start to climb and go into hover. However, at maximum speed in horizontal flight (upwind), the motors are at about 15000 rpm.

However, it is still true that when the drone is hovering (in no wind) the front motors have a slightly higher RPM than the rear motors. This is because the front of the drone is slightly heavier than the rear of the drone.

 

[zenonn]

I'm afraid I don't know exactly what you mean...

My confusion is as a result of "These speeds...", assuming it refers to all measured RPMs and at the same time "at 9639 rpm it starts to climb".
Now it's clear.

 

[Dynamicus]

I'm glad it helped you. I can talk about propellers all day if there's an audience. I bought the DJI Mini 2 just to test the upgraded propellers. I'm now thinking of a propeller shape that will allow for significantly longer battery life. I will then make a prototype propeller and measure the efficiency again. The goal is to achieve a battery life extension of 5 to 10 minutes. If I am successful, I will post a graph showing the efficiency comparison between the original propeller and the prototype propeller. This will set the stage for preparing to start mass production, that is if I can find a suitable company.

 

[scro]

How are you measuring efficiency? Is that electrical energy consumed vs thrust produced? Also, is 8% good or bad when compared to any other propeller? Such low efficiency ratios seem quite poor at first glance, but maybe they aren'twhen put into context.

I'm also curious why the graph you showed only looks at the speed range below where the motors would typically be running and excludes the more typical range used during flight. Is that because the efficiency doesnt change much beyond hover speeds, up to full thrust?

 

[zenonn]

I'm glad it helped you.

I'm not familiar with all the possible 3D printing materials, but I'm wondering, if there is a suitable material, isn't it possible to print them instead of having them manufactured by someone?
This is a very superficial reasoning, but if it is possible, then the benefit for everyone will be much greater.

 

[Dynamicus]

zenonn​

That's a good idea, but...

While I am able to model a propeller for the DJI Mini 2 that will have the same efficiency (or the same noise) as the Master Airscrew propeller, I don't have the time to look for the right propeller manufacturing technology using 3D printing (on home 3D printers). There would have to be someone here who would be willing to find the right technology to manufacture a propeller using 3D printing. If he finds such a technology, then he would post the exact instructions here on the forum. Anyone could then use such instructions to make a propeller at home. This would probably be welcomed by people who wish to use propellers in a distinctive colour.

 

[zenonn]

While I am able to model a propeller for the DJI Mini 2...​

Actually, something like that was going through my head. Unfortunately, my area of expertise is very far away, otherwise I would take up this idea with great pleasure.

 

[Dynamicus]

scro​

I believe that an efficiency of 8% is not such a bad result. But it could probably be higher, maybe 10%. If I'm right, we'll see very soon, that is if I can model a propeller with 12% (or maybe 13%) efficiency. I'm already preparing for the modelling. It's taking me a little while because I have more work to do.

I chose the meximal speed (which the graph shows) for several reasons. One reason is that at higher speeds, the steady decline in efficiency would continue anyway. A similar drop in efficiency occurs with all propeller sizes. So I'm not interested in the lowest efficiency, I'm more interested in the golden mean - when the drone is hovering in place.

 

[Pushkur]

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I like the fact it’s not just more efficient, but quieter also.

 

[rwilliam99]

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I like the fact it’s not just more efficient, but quieter also.

Fascinating - but the cost is what is going to make this difficult to go mainstream - the video said a regular boat prop was $500, and one of these was $5,000 - a 10x increase in cost. That isn't going to pencil out for cost effectiveness unless they can get the cost down significantly.

Thanks for posting the video - very interesting.

 

[Hooch33]

Or you could just buy a cheap printer, upload the cad plans and make your own.

 

[Dasher]

When considering Propeller shapes - its probably useful to recall
that propellers are just wings.
(Wings which go around in circles instead of in a straight line)

That 105% efficiency propeller mentioned above,
like most boat propellers it could replace,
has an extremely low aspect ratio.

Highly likely a poor choice for quadcopter blades,
but since most boat props are similarly low aspect ratio - it may be a good design - for boats.
(Then again, 105% improvement from terrible - is still not good - a long way from great ;-) )

Next, not sure if it is obvious, but the ad shows a boat propeller design
which is a near equivalent to a biplane wing.

Neither of these is inherently good or bad in boats or aircraft.
Your many other aircraft design constraints will guide your propeller design.

For example: Low aspect ratio wings or propellers
are never chosen for lift/drag efficiency. They are chosen
for boats for reasons including structural toughness & rigidity,
ability to resist kelp or sea grass snags, and clearance from hull
and the underwater ground.

(Hope I learned a thing or two studying aero with Red Layton
(Helicopter design genius), Frank Costin (race car designer & brother
of Cosworth Engine designer), and a couple other world class engineers & designers.)

 

[Rita..]

¿Cómo se mide la eficiencia? ¿Se consume energía eléctrica en comparación con el empuje producido? Además, ¿el 8% es bueno o malo en comparación con cualquier otra hélice? Estos índices de eficiencia tan bajos parecen bastante pobres a primera vista, pero tal vez no lo sean cuando se los pone en contexto.

También tengo curiosidad por saber por qué el gráfico que se muestra solo analiza el rango de velocidad debajo del cual normalmente estarían funcionando los motores y excluye el rango más típico utilizado durante el vuelo. ¿Es eso porque la eficiencia no cambia mucho más allá de las velocidades de vuelo estacionario, hasta alcanzar el máximo empuje?

Hola, yo tendría la misma duda. Realmente cuál sería la definición de eficiencia en este caso.

 

[Rita..]

[USUARIO=109714]scro[/USUARIO]​

Creo que una eficiencia del 8% no es un resultado tan malo. Pero probablemente podría ser mayor, quizás un 10%. Si estoy en lo cierto, lo veremos muy pronto, es decir, si puedo modelar una hélice con un 12% (o tal vez un 13%) de eficiencia. Ya me estoy preparando para el modelaje. Me está tomando un poco de tiempo porque tengo más trabajo que hacer.

Elegí la velocidad máxima (que muestra el gráfico) por varias razones. Una razón es que a velocidades más altas, la constante disminución de la eficiencia continuaría de todos modos. Se produce una caída similar en la eficiencia con todos los tamaños de hélice. Así que no estoy interesado en la eficiencia más baja, estoy más interesado en el punto medio: cuando el dron está flotando en su lugar.

¿Cuál es la definición de la eficiencia? ¿A partir de que parámetros lo calculas? Quedo a la espera