bjr981s
lvl.4
Flight distance : 139698 ft
Australia
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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
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