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--- searchwing-ardupilot-parameters [2020/03/03 01:35]
wf68spef
+++ searchwing-ardupilot-parameters [2020/07/04 02:21]
wf68spef
@@ Line 90: / Line 90: @@
 	1	BATT_VOLT_PIN	2	2
 	1	BATT_WATT_MAX	0	4
+===== RPM =====
+To measure the RPM of the motor we can use a BACK-EMF Measurement from 2 of the 3 motorcables. For more info check out the page:
+https://www.hobbywingdirect.com/products/rpm-sensor
+We connected the output pins to a AUX pin of the FC. Check out the info from Ardupilot for some info regarding the following config:
+https://ardupilot.org/copter/docs/common-rpm.html
+^Parametername      ^Value       ^Description                 ^Remark  ^
+|RPM_MAX	|100000.000000000000000000	| | |
+|RPM_MIN	|10.000000000000000000	| | |
+|RPM_MIN_QUAL	|0.100000001490116119	| | |
+|RPM_PIN	|Pin	| PIN | depending on FC |
+|RPM_SCALING	|0.143	|  |  check the hints below for this setting |
+|RPM_TYPE	|2	| AUX |  Type needs to be AUX to calc using the given sensor |
+The RPM in general can be calculated using the formula from https://www.radiocontrolinfo.com/brushless-motor-efficiency/measuring-motor-rpm/ :
+''RPM = ( 120 x Frequency ) / # of Motor Poles''
+Thats because:
+''The AC current that is produced alternates each time 2 magnetic poles pass by a winding in the stator.
+''
+As Ardupilot measures the periode duration ''dt_avg'' of the sensor rectangular signal, and calculates the RPM using
+''float rpm = scaling * (1.0e6 / dt_avg) * 60;''
+the scaling needs to correct this using
+''SCALING = ( 1 / # of Motor Poles ) * 2''
+For the Extron 800KV Motor , we have 14 Poles.
 ===== Tuning =====