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Maximum prop rpm?
3391 15 2021-2-18
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bob37
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The helicopter landing on mars today has a prop speed of 2400 rpm, which surprised me as being a bit slow in that low pressure atmosphere.  That is only 40 Hz, and the sound when taking off of my MA2 is clearly higher then that.   My question is, what is the maximum rpm of my Mavic Air 2 with both sticks full forward?  I am curious and do not find that value in the spec sheet.  

2021-2-18
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DAFlys
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My Mavic 2 shows prop speed at around 500rpm typically.
2021-2-18
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JimDandy
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We need only one piece of data to figure that out. The KV of the motors.  KV standing for 1000 rpm/volt. If you know the kv of the motors you have your answer. For instance the old Phantoms had 960 kv motors in them with a 4 cell battery you would be getting 14,208 rpm. That is figuring it at 960rpm per volt.  960 x 14.8 volts (4 cell battery) = 14,208 At full power. I have an fpv quad that is 2600kv on the motors, on a 4 cell at full throttle it is spinning at 38,480 rpm. It's fast, and fun. Having said all this, I don't know the kv of the motors in my MA2
2021-2-18
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JJB*
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Hi,

No idea what the max rpm is for the MA2, random picked 1 of my flights.
Around 10000 rpm for full power.

cheers
JJB
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2021-2-18
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DowntownRDB
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You pose a very interesting question.
2021-2-18
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bob37
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JJB* Posted at 2-18 10:31
Hi,

No idea what the max rpm is for the MA2, random picked 1 of my flights.

Where did you get that data?  My FlightRecord does not have such a column.  That would answer my question!  

I was going to tape an old iPhone onto my drone and fly it full vertical and full horizontal while audio recording the sound of the props.  Playing back into a tuner would give me the Hz and devided by 60 would give me the approximate rpm.  

But it sounds like the data is there.  Please tell me how to get it!  

Thanks,
Bob
2021-2-18
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GaryDoug
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bob37 Posted at 2-18 15:06
Where did you get that data?  My FlightRecord does not have such a column.  That would answer my question!  

I was going to tape an old iPhone onto my drone and fly it full vertical and full horizontal while audio recording the sound of the props.  Playing back into a tuner would give me the Hz and devided by 60 would give me the approximate rpm.  

Android: Look in the DJI/dji.go.v5/FlightRecord/MCDatFlightRecords folder for a .dat file with the date wanted in the name. Use the free program CSVview to open it.

JJB probably has a more elegant solution.


csvview example 1.png
2021-2-18
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DJI Stephen
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Hello there bob37. Thank you for reaching out and for these information you have posted. The DJI Mavic Air 2 has a hovering rotation speed ( average ) : 6000 rpm and a maximum rotation speed ( extreme test ) : 12300 rpm. Thank you.
2021-2-18
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JJB*
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GaryDoug Posted at 2-18 19:28
Android: Look in the DJI/dji.go.v5/FlightRecord/MCDatFlightRecords folder for a .dat file with the date wanted in the name. Use the free program CSVview to open it.

JJB probably has a more elegant solution.

yes, very elegant...   
2021-2-19
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JJB*
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bob37 Posted at 2-18 15:06
Where did you get that data?  My FlightRecord does not have such a column.  That would answer my question!  

I was going to tape an old iPhone onto my drone and fly it full vertical and full horizontal while audio recording the sound of the props.  Playing back into a tuner would give me the Hz and devided by 60 would give me the approximate rpm.  

Hi Bob,

I use FRAP; https://forum.dji.com/forum.php? ... p;extra=#pid2023752

cheers
JJB
2021-2-19
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bjr981s
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JimDandy Posted at 2-18 09:23
We need only one piece of data to figure that out. The KV of the motors.  KV standing for 1000 rpm/volt. If you know the kv of the motors you have your answer. For instance the old Phantoms had 960 kv motors in them with a 4 cell battery you would be getting 14,208 rpm. That is figuring it at 960rpm per volt.  960 x 14.8 volts (4 cell battery) = 14,208 At full power. I have an fpv quad that is 2600kv on the motors, on a 4 cell at full throttle it is spinning at 38,480 rpm. It's fast, and fun. Having said all this, I don't know the kv of the motors in my MA2

You have most of the data correct. Indeed the KV of the motor will define the revs per volt of voltage applied to the motor.

But You have missed a few things. The first is that the Voltage of the battery drops as it depletes so the max also drops as it depletes.

So the max is the max battery voltage. x KV. But you missed that DJI don't use LiPo batteries. They use LiHV batteries so a 4 cell is 4 x 4.4V an extra .2V per cell so 16.8V on a fully charged battery.

The last thing is that the KV value is accurate only without propellers. It's a static no load figure.

The actual real result of max RPM based on the load the props have on the motor. That is the Pitch, Length and number of blades on the prop.

The in flight max will be a percentage of the KV and Voltage. Where no load will be 100%, and the load will be below this in flight by a percentage that relates to the load the props place on the motors.

All important factors when you are designing your own propulsion system for your drone.

Including battery requirements C ratings, ESC ratings etc.

DJI provide for those of us that build our own special purpose drones "Tuned Propulsion Systems'

You can see them here.

https://www.dji.com/au/e5000?site=brandsite&from=insite_search

Cheers


2021-2-19
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JimDandy
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DJI Stephen Posted at 2-18 19:52
Hello there bob37. Thank you for reaching out and for these information you have posted. The DJI Mavic Air 2 has a hovering rotation speed ( average ) : 6000 rpm and a maximum rotation speed ( extreme test ) : 12300 rpm. Thank you.

Hello there bob37. Thank you for reaching out and for these information you have posted. The DJI Mavic Air 2 has a hovering rotation speed ( average ) : 6000 rpm and a maximum rotation speed ( extreme test ) : 12300 rpm. Thank you.

Thanks DJI Stephen, the kv is similar to the old phantom, The calculations are there supporting a four cell pack.  A good choice for doing what we need in a camera ship, long flight, a decent amount of power.Your not going to get long flight times if you increase the kv of the motors. It's a delicate balance between performance and time. My Freestyle quad with 2600kv motors flies for 4 minutes on 4 cells 1300 mah. and thats not being to aggressive with it. DJI has the motor match of power and performance down to a science. long flight times, with enough power to cut a bit of wind.
2021-2-19
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JimDandy
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bjr981s Posted at 2-19 00:36
You have most of the data correct. Indeed the KV of the motor will define the revs per volt of voltage applied to the motor.

But You have missed a few things. The first is that the Voltage of the battery drops as it depletes so the max also drops as it depletes.

Thank you for the reply, Yes, the props and and # of blades do affect the "speed" of the motor.  The data i showed is with no no prop on and fairly raw. Gets you in the ball park. Thank you again
2021-2-19
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bob37
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DJI Stephen Posted at 2-18 19:52
Hello there bob37. Thank you for reaching out and for these information you have posted. The DJI Mavic Air 2 has a hovering rotation speed ( average ) : 6000 rpm and a maximum rotation speed ( extreme test ) : 12300 rpm. Thank you.

Thank you everyone!  
2021-2-19
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DJI Stephen
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bob37 Posted at 2-19 07:14
Thank you everyone!

Hi there bob37. Thank you for the reply and you are very much welcome. If you have any other inquiries or any concerns with DJI. Please feel free to post it here at DJI Forum. We are all here to help and support you. Thank you.
2021-2-22
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djiuser_OsRvnoHlftN4
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Thanks for the information on this. I really enjoy the information.
2021-6-17
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