3-Blade propeller for MP1 ?

[FoxhallGH]

Thanks. The P-61 engine was the same that was adopted for the F4U in it's later years. The R2800 double wasp.

The Corsair was/is a beautiful aircraft, but took a lot of skill to fly ... Prop was so huge in diameter, they had to make those unique W wings to get it away from the deck when on the ground, and it had to fly a curved approach to a carrier because the nose was so long & high it blocked the view. Some interesting books about WW2 carrier op's with F4U's out there ...

 

[mnis]

My qualifications are in Telecom's and IT, so I'm no aeronautical engineer either.
The assumption about moving more air with the 3-blade prop', simply comes from the fact that you have 30% more propulsion blades on a 3-bladed prop, than you have on 2 ...
The study about 3 bladed prop's having less efficiency may be quite true. At the speed a Mavic's prop's rotate (4,500 rpm +), the tips of the propellers create an immense disturbance between the air that is being pushed back, and less than a mm away air that is not being 'pushed' by the prop at all! That disturbance is given a little time to clear when you have two blades, but with 3, you can have the situation where the blade tips are continuously running into the disturbance ('cavitation') caused by the previous blade. That's why sometimes you get worse results for multi-blade prop's - and it's also why you'll see a lot of strange curved prop' designs on aircraft that use propellers rather than jet engines.

In regard to the motors ... You have a fixed Voltage that is applied to the motor control . The Mavic motors are a design where an alternating current is applied to coils around the outside of the motor, to literally 'pull' the central 'stator' around on its shaft causing the attached prop' to spin. I think there may actually be a 3-phase control i.e. not a single wave going around the motor coils, but 3 - 120 degrees apart. My understanding of how the motor control works is that by varying the frequency of that alternating current, you drag the stator faster and get more thrust, or you 'brake' it to slow it down and get less. The balance of that between the 4 motors then gives you the directional control. I believe that the Mavic Pro uses a square-wave switching to control the motors, but the Mavic Pro Platinum, and the Pro 2 range use a more advanced sine-wave AC control making the control of the motors a lot smoother.

[Edit:] Correction to the above ... The Mavic 'brushless' motors actually have the coils wound on the central 'fixed' stator, with magnets on the moving drum that is attached to the prop'. Unlike conventional electric motors, its the outside drum that spins, while the central shaft is fixed.
View attachment 55369 View attachment 55370

Some info here ... How A Quadcopter Works With Propellers And Motors Explained

Thank you for the effort to explain it to me. Today it was rainy and stormy. But there will be a few mild days in between. Then with my Mavic Pro I will try to find out how big the differences between 2 and 3 blade propellers really are. Also, I'm currently looking for a way somewhere safe to fly inside. Let's see what happens. Of course I will share my results here.

 

[mnis]

I tried to "hand catch" my Mavic Pro once, and got my fingers up too far. The original blade hit my finger, and it was VERY painful. It felt like it got hit with a whip. I thought for sure that it cut the tip of my finger off - but was relieved to see it wasn't even bleeding, or even scuffed! I attribute this to the fact that the original Mavic blades ARE flexible. If I was using a stiffer blade (carbon fiber), I may not have my fingertip any more. This is all theory, IMHO. I'm not about to do a study, although it sounds like a good project for Mythbusters - wish that show was still on...

That was courageous and very dangerous at the same time. Good that nothing worse has happened...[emoji15]

I do not really understand the need to take such a risk. So far, I've always found ways to start and land on safe ground and areas. I have never tried to start or land near my face. It is less about losing my pretty face, but about keeping the basic functionality, such as my facial expressions...[emoji12]

Basically, I do not fly in close proximity to the public. Of course, I do not want to endanger anyone. We are always committed to keeping all those involved and those not involved in the best possible way against risks...[emoji56]

I would use my 3-blade propellers if a) maneuvers the aircraft much more stably through the air, and b) if the maximum flight time is only slightly reduced...[emoji57]

 

[D Hansel]

Actually, 3-bladed prop's ARE more efficient than 2-bladed as more air is pushed back for each rotation of the propeller. Correct however, in that the overall diameter of the propeller can be reduced, to get the same effect as a larger diameter 2-bladed prop'. Since you already have the clearance for the stock 2-bladed prop on your Mavic, putting a lesser diameter 3-bladed prop' on the Mavic is really not going to give you any advantages (it may actually slow the roll rate!). If you had a 3-blade prop' that was the same diameter and pitch as the stock 2-blade, then you may get into issues about overworking the motors etc. A 3-bladed prop with a lesser pitch would spin faster, and its that rotational speed through the air that generates the prop noise! So - its hard to see where the advantages are for us in 3-blade props for the Mavic Pro range.

I would imagine that DJI has tried all types of configurations on the props and settled on what they sell. You have to take into consideration the load and stress on the motors.

 

[mnis]

I would imagine that DJI has tried all types of configurations on the props and settled on what they sell. You have to take into consideration the load and stress on the motors.

I want to claim:
The original MP1 propellers are certainly not optimal in terms of performance.

In addition, DJI is little interested in further optimizing the old product line on a large scale. Latest findings go into new products ...

The original MP1 propellers have been optimized in terms of foldability and application security.
Rigid 2-blade propellers (identical blade profile) that can not be folded work more efficiently. You will get about 4 percent more flight time, even if the propellers were not foldable.

The engines and ESC's will come up with a bit more base load. There are enough videos and footage about what some users treat this quad to extra weight. And for a maximum speed of 65 km / h, a lot more power is required. A multiple of the MP1 weight can be moved through the air.

Problems arise only when using an unmodified battery. The battery is not suitable for significantly more weight and for intensive use of the sport mode ...

 

[mnis]

Imagine the following:
The MP1 battery weighs a total of 235 grams, housing and electronics require max. 45 grams. The arrangement of the three battery cells (190g) is horizontal.

Take six cells and arrange them vertically. If you keep the 3S configuration, you get twice the capacity of 7660mAh. About 20 grams would be required for a higher case. The new battery would weigh 445 grams, and go not so much beyond the total height. The propellers and the balance of the MP1 would not be negatively affected.

Without further optimization you will receive the following:
- Double the time required for the standard 1C charging.
- Doubling the maximum possible power output, resulting in lower self-heating.
- Up to 50 percent longer flight times from 27 to max. 40.5 minutes
- The vertically positioned battery cells will expand horizontally in the event of overload, and may not push out of the battery compartment so quickly that a safe landing without disconnecting from the power port is more likely.

Everything just a dream?
I mean it is possible without much effort ...

The quadrocopter might lose some agility and portability, but stay longer without battery changes in the air for continuous filming ...

 

[FoxhallGH]

I have done the Flight Duration Test today, to compare DJI Stock prop's to Carbon Fibre versions. So - here is the equipment, method and results:

Equipment
Drone: Mavic Pro Platinum [MPP]
Prop's flown: Hensych 8331 carbon-fibre (exact copy of stock DJI 'quiet' prop for MPP) - compared with DJI stock 8331 'quiet' Platinum props.
DJI Stock on left, Hensych CF on right.
Both prop-sets are 8.3" (210.8 mm) in diameter, with a pitch of 3.1" (78.7 mm)

Objectives
Carbon Fibre [CF] prop's are stiffer and typically show lower rpm readings on the DJI RC Controller. Is flight duration improved when using CF prop's over the stock DJI prop's of the same shape/profile?

Method
Low battery alert was set at 15%, and critical battery at 10% ... I used the auto-takeoff button on the DJI Go 4 app' to allow the MPP to start, and ascend to 1.2 metres without any further control intervention for both prop tests. I then immediately set 'Terrain Follow' mode to maintain height and override any height changes requested by RTH etc. I turned on video record prior to takeoff and ran that for the duration of the flight (as an alternative confirmation of flight time if needed). The MPP was then just left to hover above the take-off point with no control inputs until the battery got to critical and the Drone landed itself. RTH and low battery warnings were ignored in Go 4 - and the MPP just left to descend when it wanted to.
There were some light cross-wind gusts during the tests, but these would have been less than 2 metres/sec. max.
Flight logs were exported to DJI Flight Log Viewer - Phantom Help and the resulting tables were used to determine the exact time that the MPP provided RTH warning, and then when it touched down (i.e. the exact logged flight-time it attained minimal IMU Altitude).
The two batteries used were manufactured in December 2017 with one having 9 charge cycles and the other having 11.

Results
Hensych 8331 carbon-fibre prop's
[Using my battery # 3 ... 9 cycles]
Go 4 popped RTH notifications at 22 minutes 51.5 seconds into the flight
Minimum IMU altitude was recorded at 25 minutes 48.3 seconds into the flight
Motor rpm was observed on the controller to be varying between approx. 464 and 473 prm x10 during the hover

DJI stock 8331'quiet' prop's
[Using my battery #2 ... 11 cycles]
Go 4 popped RTH notifications at 24 minutes 30.5 seconds into the flight
Minimum IMU altitude was recorded at 24 minutes 49.3 seconds into the flight
Motor rpm was observed on the controller to be varying between approx. 497 and 513 prm x10 during the hover

Observations
1) The first test using the CF prop's ended differently to the second using stock DJI. Although the MPP had issued critical battery warning's during the first test, it continued to hover for about a minute after the warning was given, and the Go 4 app' showed --/-- battery remaining while it was in the hover. The second test was different in that the critical battery warning was given and the MPP then landed within seconds afterwards.
2) For the reasons in 1) above, it may be more indicative to use the "The remaining battery is only enough for RTH. Return home now." warning points for the purposes of comparing flight duration.
3) Stability while hovering was slightly but perceptibly better with the Hensych 8331 CF prop's. The presence of a cross-wind during the test made this more apparent, and while vertical movement on the video footage taken during the two flights is minimal, the flight with the stock DJI prop's shows MORE sideways movement as the drone was buffeted through yaw and roll. This movement is apparent on the video for both tests, but is more 'violent' and ranges further when the MPP is flying stock DJI prop's.
4) Based on the point at which the logs show "The remaining battery is only enough for RTH. Return home now." - the stock DJI 8331 prop's are providing the best flight duration (this warning came about 2 minutes later than when flying the CF prop's).
5) A second test run would be wise, swapping the battery/prop combination - to ensure that battery 'difference' is not a factor in this test.
6) No sound measurement [dB] tests were carried out, but the CF prop's have a lower frequency 'hum' than the stock DJI in the hover, and therefore sound quieter then the 'quiet' DJI prop's.

Conclusions
Earlier observations showed a lower rpm reading on the RC controller when the MPP was being flown on Hensych 8331 carbon-fibre prop's. The combination of the lower rpm, and the slightly shorter flight duration seen in these tests, seems to prove that the carbon-fibre prop's are making the Mavic's motors work harder, and therefore they draw more current from the battery - and consequently decrease flight duration.
It was outside the scope of this test, but improvement in stability appears to be a trade-off against flight duration when flying carbon-fibre prop's.
Ideally - both test flights should probably be carried out using the same battery to ensure that there are no issues in the test that are effected by a difference between batteries. However, battery charging time will introduce a significant delay between the two tests, that could lead to comparison issues due to weather and other atmospheric effects.

 

[mnis]

Super detailed test ... But you mentioned it yourself, the batteries could have different capacities and distort your results. This is not necessarily directly related to charge cycles and age. When using different batteries, the actual available capacity of each battery must be known. Otherwise, it is better to use a single battery for both tests. I have five batteries produced in 2017-02 and bought 2017-05. Here are currently the capacities between 99.1 and 94.9 percent, based on the manufacturer's information (100% = 3830mAh).

 

[FoxhallGH]

Super detailed test ... But you mentioned it yourself, the batteries could have different capacities and distort your results. This is not necessarily directly related to charge cycles and age. When using different batteries, the actual available capacity of each battery must be known. Otherwise, it is better to use a single battery for both tests. I have five batteries produced in 2017-02 and bought 2017-05. Here are currently the capacities between 99.1 and 94.9 percent, based on the manufacturer's information (100% = 3830mAh).

Agreed - Not only was I concerned about the differences between the two batteries, but the combination of my Mavic & #3 battery seemed to ignore the critical warning and carried on flying until the battery zeroed. The flight with the #2 battery landed pretty much as soon as the critical warning popped up on Go 4.

 

[mnis]

Agreed - Not only was I concerned about the differences between the two batteries, but the combination of my Mavic & #3 battery seemed to ignore the critical warning and carried on flying until the battery zeroed. The flight with the #2 battery landed pretty much as soon as the critical warning popped up on Go 4.

That does not sound good.
I never had a similar situation without warnings with my batteries. But without warnings I would have forced the landing between 30 and 20 percent!

Only once did I ignore all warnings during a stamina test. My MP1 crashed at 6 percent remaining capacity on soft ground, and then was without visible damage on the back...[emoji28]

It was a terribly scary moment for me. The battery had shut itself off. Since then, exactly this #3 battery has the lowest capacity (about 3600mAh) of all.

Flights below this 33 percent limit are of course possible...

But it's the hottest zone of the battery!

And DJI also says:
You can fly up to xx minutes...
However, they conceal a significant fact, because it can have an extremely negative impact on the battery life.

Only once flying far below the last 33 percent can thus permanently have capacity loss. This zone is also the big trigger for bursting batteries...

Now I would test differently:
- I would use a full battery with previously measured capacity.
- I would have a defined time of maybe max. 15 minutes to make the hover test.
- After that, I would determine the remaining capacity of the battery by gently discharging, and calculate the expected remaining flight time.

This can be achieved with little risk and effort.

Otherwise, I would test all the propeller-setups with a single battery, and (... according to the displayed battery status on the RC remote) quit after 66 percent battery consumption each test...

 

[FoxhallGH]

This is an interesting vid' about running batteries down to the wire ...

When the controller show's 0% battery, it appears that there is still around 9 V left in the battery (Mavic Pro). i.e. 0% doesn't mean 0 Volts.

 

[mnis]

This is an interesting vid' about running batteries down to the wire ...

When the controller show's 0% battery, it appears that there is still around 9 V left in the battery (Mavic Pro). i.e. 0% doesn't mean 0 Volts.

Interesting and confusing for me at the same time.

I currently have 7 batteries (5x DJI & 2x Powerextra) for my MP1, and without exception, all batteries turn off automatically as soon as 9.90 volts (3.30 volts per cell) are below.

A battery may behave differently during discharge in the MP, but that is in conflict with my findings.

But no matter ...
The shown should never be done. It is only legitimate in emergencies.

With rechargeable batteries, reaching the discharge end voltage equals 0 percent remaining capacity, and never 0 volts.

LiPo's and LiHv's are considered discharged at 3.30 volts per cell. If the battery continues to be discharged, irreversible loss of capacity will result, up to total failure. At a cell voltage below 2.50 volts, a dead battery cell is assumed. A brief drop below the voltage limits may not lead to failure immediately, but should be prevented in principle ...

 

[SIDEHACK]

Interesting and confusing for me at the same time.

I currently have 7 batteries (5x DJI & 2x Powerextra) for my MP1, and without exception, all batteries turn off automatically as soon as 9.90 volts (3.30 volts per cell) are below.

A battery may behave differently during discharge in the MP, but that is in conflict with my findings.

But no matter ...
The shown should never be done. It is only legitimate in emergencies.

With rechargeable batteries, reaching the discharge end voltage equals 0 percent remaining capacity, and never 0 volts.

LiPo's and LiHv's are considered discharged at 3.30 volts per cell. If the battery continues to be discharged, irreversible loss of capacity will result, up to total failure. At a cell voltage below 2.50 volts, a dead battery cell is assumed. A brief drop below the voltage limits may not lead to failure immediately, but should be prevented in principle ...

I could not agree more! Low voltage is a LiPo batterys worst enemy. When I first got involved with drones a few years ago I murdered many a LiPo before I decided to read the directions ....... Just change the battery more frequently. We are supposed to be flying LOS anyway.

 

[hermitdog]

My 3-blade propellers arrived from China today - and I wasted no time getting out there to try them out.

First, I was truly impressed by how quiet they are. Although I don't have sophisticated Db meters, they are noticeably quieter. I want to say 50% quieter, but that's a subjective judgment.

I launched, went to 200 feet, and flew about two miles from my launch point in NO wind. Excellent steering control; switched to Sport Mode halfway to see the maximum speed I could get - only about 30 mph. I have not yet tested the claim that 3-blade props will increase flight time, although that seems likely to be the case: This first round-trip flight took ten minutes, and my RC said I still had 18 minutes remaining in the battery when I landed. That figure might have been even higher if I'd not flown half of the mission in Sport Mode.

The sun is VERY bright today, and I noticed that when flying home, the video caught some shadow from the props. At one point I got an "Obstacle" warning message - at 200 feet - I'm sure that was due to a lens reflection of direct sunlight. A slight alteration in direction of flight cleared it up.

All in all, I'm delighted with my new 3-blade props: https://www.amazon.com/HeiyRC-Propeller-3-Blade-Replacement-Accessory/dp/B07JG3YTFB/ref=sr_1_4?ie=UTF8&qid=1545167917&sr=8-4&keywords=3-blade+propeller+for+Mavic+Pro

 

[mnis]

My 3-blade propellers arrived from China today - and I wasted no time getting out there to try them out.

First, I was truly impressed by how quiet they are. Although I don't have sophisticated Db meters, they are noticeably quieter. I want to say 50% quieter, but that's a subjective judgment.

I launched, went to 200 feet, and flew about two miles from my launch point in NO wind. Excellent steering control; switched to Sport Mode halfway to see the maximum speed I could get - only about 30 mph. I have not yet tested the claim that 3-blade props will increase flight time, although that seems likely to be the case: This first round-trip flight took ten minutes, and my RC said I still had 18 minutes remaining in the battery when I landed. That figure might have been even higher if I'd not flown half of the mission in Sport Mode.

The sun is VERY bright today, and I noticed that when flying home, the video caught some shadow from the props. At one point I got an "Obstacle" warning message - at 200 feet - I'm sure that was due to a lens reflection of direct sunlight. A slight alteration in direction of flight cleared it up.

All in all, I'm delighted with my new 3-blade props: https://www.amazon.com/HeiyRC-Propeller-3-Blade-Replacement-Accessory/dp/B07JG3YTFB/ref=sr_1_4?ie=UTF8&qid=1545167917&sr=8-4&keywords=3-blade+propeller+for+Mavic+Pro

That seems to be exactly the same propeller that I got. I am pleased to read that the propellers seem to work well.

 

[mnis]

30mph may not be enough for some, but hey it's not a racing machine.

 

[FoxhallGH]

My 3-blade propellers arrived from China today - and I wasted no time getting out there to try them out.

First, I was truly impressed by how quiet they are. Although I don't have sophisticated Db meters, they are noticeably quieter. I want to say 50% quieter, but that's a subjective judgment.

I launched, went to 200 feet, and flew about two miles from my launch point in NO wind. Excellent steering control; switched to Sport Mode halfway to see the maximum speed I could get - only about 30 mph. I have not yet tested the claim that 3-blade props will increase flight time, although that seems likely to be the case: This first round-trip flight took ten minutes, and my RC said I still had 18 minutes remaining in the battery when I landed. That figure might have been even higher if I'd not flown half of the mission in Sport Mode.

The sun is VERY bright today, and I noticed that when flying home, the video caught some shadow from the props. At one point I got an "Obstacle" warning message - at 200 feet - I'm sure that was due to a lens reflection of direct sunlight. A slight alteration in direction of flight cleared it up.

All in all, I'm delighted with my new 3-blade props: https://www.amazon.com/HeiyRC-Propeller-3-Blade-Replacement-Accessory/dp/B07JG3YTFB/ref=sr_1_4?ie=UTF8&qid=1545167917&sr=8-4&keywords=3-blade+propeller+for+Mavic+Pro

Great feedback on the new prop's and would be interested to hear more about them ... What rpm range are you seeing in the hover?

 

[STUFF2C]

Has anyone weighed each blade individually to check for balance?

 

[mnis]

And here's what I got yesterday:View attachment 55153View attachment 55154View attachment 55155View attachment 55156View attachment 55157View attachment 55158View attachment 55159View attachment 55160View attachment 55161View attachment 55162

I think a lot of effort has been invested in offering a good product. Anyway, each of my 3-blade propellers weighs exactly 11.8 grams. I do not know any more yet ...

 

[Pepzki]

Flight time? Any errors? I got motor over current error/battery current errors with my parameter modded mavic pro in colder weather with silence platinum props.