AP_Soaring: added SOAR_ENABLE_CH parameter

libraries/AP_Soaring/AP_Soaring.cpp

@@ -117,6 +117,13 @@ const AP_Param::GroupInfo SoaringController::var_info[] = {
     // @Range: 0 1000.0
     // @User: Advanced
     AP_GROUPINFO("ALT_CUTOFF", 14, SoaringController, alt_cutoff, 250.0),
+    
+    // @Param: ENABLE_CH
+    // @DisplayName: (Optional) RC channel that toggles the soaring controller on and off
+    // @Description: Toggles the soaring controller on and off. This parameter has any effect only if SOAR_ENABLE is set to 1 and this parameter is set to a valid non-zero channel number. When set, soaring will be activated when RC input to the specified channel is greater than or equal to 1700.
+    // @Range: 0 16
+    // @User: Advanced
+    AP_GROUPINFO("ENABLE_CH", 15, SoaringController, soar_active_ch, 0),
 
     AP_GROUPEND
 };
@@ -382,5 +389,13 @@ float SoaringController::McCready(float alt)
 
 bool SoaringController::is_active()
 {
-    return soar_active;
+    if (!soar_active) {
+        return false;
+    }
+    if (soar_active_ch <= 0) {
+        // no activation channel
+        return true;
+    }
+    // active when above 1700
+    return hal.rcin->read(soar_active_ch-1) >= 1700;
 }

libraries/AP_Soaring/AP_Soaring.h

@@ -67,6 +67,7 @@ class SoaringController {
 
 protected:
     AP_Int8 soar_active;
+    AP_Int8 soar_active_ch;
     AP_Float thermal_vspeed;
     AP_Float thermal_q1;
     AP_Float thermal_q2;