Built in RPM

alokbhargava

Premium Pilot
Joined
Sep 28, 2015
Messages
6,943
Reaction score
2,322
Location
San Francisco, CA
Where did you learn this from? Any reference?


Sent from my iPhone using PhantomPilots
 
Joined
Aug 24, 2016
Messages
157
Reaction score
24
Age
57
Location
Long Island, New York
Was flying yesterday Near Fire Island New York after looking on the Go App bottom left i was trying to find the orientation of my P4 clicked on the GPS and saw RPM of the 4 Motors each was slightly different in the 5350 area never seen this before.
 
Joined
Jun 26, 2015
Messages
6,027
Reaction score
2,687
Location
Yorba Linda, CA
Was flying yesterday Near Fire Island New York after looking on the Go App bottom left i was trying to find the orientation of my P4 clicked on the GPS and saw RPM of the 4 Motors each was slightly different in the 5350 area never seen this before.
Yep, and when you hit around 8000 RPM in thin air (12,000'MSL) and high winds, you'll get an RPM MAX warning.
 
Joined
Apr 6, 2016
Messages
87
Reaction score
29
Location
New Zealand
Being a brush-less motor, it is a simplified AC motor which is commutated by pulsing the winding pairs - therefore the speed of the motor can be very accurately and directly deduced by the number of commutations per second fed to the motor divided by the number of phases (assuming no slippage - unlikely to slip in this motor), not as per the calculation shown in your' link which talks of a normal or brush commutated DC motor.

Phantom 4 motor: Inside a Drone – Brushless Motors
 
  • Like
Reactions: Mike_Flys
Joined
Jan 4, 2016
Messages
7,828
Reaction score
3,087
Location
Australia
Being a brush-less motor, it is a simplified AC motor which is commutated by pulsing the winding pairs - therefore the speed of the motor can be very accurately and directly deduced by the number of commutations per second fed to the motor divided by the number of phases (assuming no slippage - unlikely to slip in this motor), not as per the calculation shown in your' link which talks of a normal or brush commutated DC motor.

Phantom 4 motor: Inside a Drone – Brushless Motors
Why do you say it's a simplified AC motor? It may have fixed magnets on the rotor but it is a typical AC induction motor.

The speed can be accurately determined for a given line frequency (suspect this is what you mean by "commutations") but not by simply dividing line frequency by number of phases. It is the number of poles that is important, the motor may be single phase and the speed can still be determined.

Your link shows 18 colis on the stator making it a 6 pole 3 phase motor. The motor speed in RPM will be line frequency * 60 divided by 2/number or poles.
 

alokbhargava

Premium Pilot
Joined
Sep 28, 2015
Messages
6,943
Reaction score
2,322
Location
San Francisco, CA
OP had assumed that there are built in RPM sensors in motors and my answer was NO as there are indirect ways to calculate motor RPM. I just picked up one article from the net as an example to show the calculations.


Sent from my iPhone using PhantomPilots
 
  • Like
Reactions: Aotearoa Kiwi
Joined
Apr 6, 2016
Messages
87
Reaction score
29
Location
New Zealand
Why do you say it's a simplified AC motor? It may have fixed magnets on the rotor but it is a typical AC induction motor.
The proper tech name for it is a BLDC motor or BrushlLess DC motor, but I think we are on the same wavelength just in different ways

For anyone interested, here is a wiki article that explains probably better than I did...
Brushless DC electric motor - Wikipedia
 
Joined
Jan 4, 2016
Messages
7,828
Reaction score
3,087
Location
Australia
The proper tech name for it is a BLDC motor or BrushlLess DC motor, but I think we are on the same wavelength just in different ways

For anyone interested, here is a wiki article that explains probably better than I did...
Brushless DC electric motor - Wikipedia
They arent BLDC motors on the current and recent DJI gear, these motors are driven by a sinusoidal waveform (sine wave). These are true synchronous AC induction motors where the speed is locked to and directly determined by line frequency rather than pulsed DC.
 
Last edited:
Joined
Nov 16, 2014
Messages
48
Reaction score
2
Was flying yesterday Near Fire Island New York after looking on the Go App bottom left i was trying to find the orientation of my P4 clicked on the GPS and saw RPM of the 4 Motors each was slightly different in the 5350 area never seen this before.

Are you talking about clicking on the Radar circle? If so when I click on that nothing happens...

Jacl
 
Joined
Jan 19, 2016
Messages
1,626
Reaction score
418
Age
45
Was flying yesterday Near Fire Island New York after looking on the Go App bottom left i was trying to find the orientation of my P4 clicked on the GPS and saw RPM of the 4 Motors each was slightly different in the 5350 area never seen this before.
Wouldn't the change of the RPMs be because of the ESCs being told by the flight board what to do based on the wind?
 

New Threads

Forum statistics

Threads
135,857
Messages
1,405,542
Members
98,908
Latest member
Tom Jennings