Copter: add flight option to relase gripper on thrust loss

ArduCopter/Copter.h

@@ -606,6 +606,7 @@ private:
     enum class FlightOptions {
         DISABLE_THRUST_LOSS_CHECK     = (1<<0),   // 1
         DISABLE_YAW_IMBALANCE_WARNING = (1<<1),   // 2
+        RELEASE_GRIPPER_ON_THRUST_LOSS = (1<<2),  // 4
     };
 
     static constexpr int8_t _failsafe_priorities[] = {

ArduCopter/Parameters.cpp

@@ -1042,7 +1042,7 @@ const AP_Param::GroupInfo ParametersG2::var_info[] = {
     // @Param: FLIGHT_OPTIONS
     // @DisplayName: Flight mode options
     // @Description: Flight mode specific options
-    // @Bitmask: 0:Disable thrust loss check, 1:Disable yaw imbalance warning
+    // @Bitmask: 0:Disable thrust loss check, 1:Disable yaw imbalance warning, 2:Release gripper on thrust loss
     // @User: Advanced
     AP_GROUPINFO("FLIGHT_OPTIONS", 44, ParametersG2, flight_options, 0),
 

ArduCopter/crash_check.cpp

@@ -163,6 +163,12 @@ void Copter::thrust_loss_check()
         // enable thrust loss handling
         motors->set_thrust_boost(true);
         // the motors library disables this when it is no longer needed to achieve the commanded output
+
+#if GRIPPER_ENABLED == ENABLED
+        if ((copter.g2.flight_options & uint32_t(FlightOptions::RELEASE_GRIPPER_ON_THRUST_LOSS)) != 0) {
+            copter.g2.gripper.release();
+        }
+#endif
     }
 }