Display ESC telemetry as real RPM in the OSD

The telemetry data provides eRPM/100.  Added a `motor_poles` parameter (defaulting to 14) that is used to calculate the physical RPM.

RPM = (telemetry_rpm * 100) / (motor_poles / 2)

Most motors we commonly use are 14 poles, but the user can adjust if needed for their setup.

Also calculate actual RPM for DEBUG_ESC_SENSOR_RPM, but to fit with in int16 the log value will be RPM/10.

src/main/flight/mixer.c

@@ -110,6 +110,8 @@ void pgResetFn_motorConfig(motorConfig_t *motorConfig)
             motorIndex++;
         }
     }
+
+    motorConfig->motorPolesCount = 14;   // Most brushes motors that we use are 14 poles
 }
 
 PG_REGISTER_ARRAY(motorMixer_t, MAX_SUPPORTED_MOTORS, customMotorMixer, PG_MOTOR_MIXER, 0);

src/main/flight/mixer.h

@@ -101,6 +101,7 @@ typedef struct motorConfig_s {
     uint16_t minthrottle;                   // Set the minimum throttle command sent to the ESC (Electronic Speed Controller). This is the minimum value that allow motors to run at a idle speed.
     uint16_t maxthrottle;                   // This is the maximum value for the ESCs at full power this value can be increased up to 2000
     uint16_t mincommand;                    // This is the value for the ESCs when they are not armed. In some cases, this value must be lowered down to 900 for some specific ESCs
+    uint8_t motorPolesCount;                // Magnetic poles in the motors for calculating actual RPM from eRPM provided by ESC telemetry
 } motorConfig_t;
 
 PG_DECLARE(motorConfig_t, motorConfig);

src/main/interface/settings.c

@@ -554,6 +554,7 @@ const clivalue_t valueTable[] = {
     { "motor_pwm_protocol",         VAR_UINT8  | MASTER_VALUE | MODE_LOOKUP, .config.lookup = { TABLE_MOTOR_PWM_PROTOCOL }, PG_MOTOR_CONFIG, offsetof(motorConfig_t, dev.motorPwmProtocol) },
     { "motor_pwm_rate",             VAR_UINT16 | MASTER_VALUE, .config.minmax = { 200, 32000 }, PG_MOTOR_CONFIG, offsetof(motorConfig_t, dev.motorPwmRate) },
     { "motor_pwm_inversion",        VAR_UINT8  | MASTER_VALUE | MODE_LOOKUP, .config.lookup = { TABLE_OFF_ON }, PG_MOTOR_CONFIG, offsetof(motorConfig_t, dev.motorPwmInversion) },
+    { "motor_poles",                VAR_UINT8 | MASTER_VALUE, .config.minmax = { 4, 32 }, PG_MOTOR_CONFIG, offsetof(motorConfig_t, motorPolesCount) },
 
 // PG_THROTTLE_CORRECTION_CONFIG
     { "thr_corr_value",             VAR_UINT8  | MASTER_VALUE, .config.minmax = { 0,  150 }, PG_THROTTLE_CORRECTION_CONFIG, offsetof(throttleCorrectionConfig_t, throttle_correction_value) },

src/main/io/osd.c

@@ -820,7 +820,7 @@ static bool osdDrawSingleElement(uint8_t item)
 
     case OSD_ESC_RPM:
         if (feature(FEATURE_ESC_SENSOR)) {
-            tfp_sprintf(buff, "%5d", escDataCombined == NULL ? 0 : escDataCombined->rpm);
+            tfp_sprintf(buff, "%5d", escDataCombined == NULL ? 0 : (escDataCombined->rpm * 100) / (motorConfig()->motorPolesCount / 2));
         }
         break;
 #endif

src/main/sensors/esc_sensor.c

@@ -264,7 +264,7 @@ static uint8_t decodeEscFrame(void)
 
         frameStatus = ESC_SENSOR_FRAME_COMPLETE;
 
-        DEBUG_SET(DEBUG_ESC_SENSOR_RPM, escSensorMotor, escSensorData[escSensorMotor].rpm);
+        DEBUG_SET(DEBUG_ESC_SENSOR_RPM, escSensorMotor, (escSensorData[escSensorMotor].rpm * 10) / (motorConfig()->motorPolesCount / 2)); // output actual rpm/10 to fit in 16bit signed.
         DEBUG_SET(DEBUG_ESC_SENSOR_TMP, escSensorMotor, escSensorData[escSensorMotor].temperature);
     } else {
         frameStatus = ESC_SENSOR_FRAME_FAILED;