Plane: Add fwd. throttle cutoff voltage parameter

ArduPlane/Parameters.cpp

@@ -1309,7 +1309,16 @@ const AP_Param::GroupInfo ParametersG2::var_info[] = {
     // @User: Standard
     AP_GROUPINFO("RNGFND_LND_ORNT", 36, ParametersG2, rangefinder_land_orient, ROTATION_PITCH_270),
 #endif
-
+
+    // @Param: FWD_BAT_THR_CUT
+    // @DisplayName: Forward throttle cutoff battery voltage
+    // @Description: The estimated battery resting voltage below which the throttle is cut in auto-throttle modes. Measured on the battery used for forward throttle compensation (FWD_BAT_IDX). If set to zero, the throttle will not be cut due to low voltage, allowing the motor(s) to continue running until the battery is depleted. This should be set to the minimum operating voltage of you motor(s) or to a voltage level where minimal thrust is produced, to conserve the remaining battery power for the electronics and actuators.
+    // @Range: 0 35
+    // @Units: V
+    // @Increment: 0.1
+    // @User: Standard
+    AP_GROUPINFO("FWD_BAT_THR_CUT", 37, ParametersG2, fwd_batt_cmp.batt_voltage_throttle_cutoff, 0.0f),
+
     AP_GROUPEND
 };
 

ArduPlane/Parameters.h

@@ -556,6 +556,7 @@ class ParametersG2 {
 
         AP_Float batt_voltage_max;
         AP_Float batt_voltage_min;
+        AP_Float batt_voltage_throttle_cutoff;
         AP_Int8  batt_idx;
 
     private:

ArduPlane/servos.cpp

@@ -440,6 +440,19 @@ void ParametersG2::FWD_BATT_CMP::update()
 // Apply throttle scale to min and max limits
 void ParametersG2::FWD_BATT_CMP::apply_min_max(int8_t &min_throttle, int8_t &max_throttle) const
 {
+    // Cut off throttle if FWD_BAT_IDX battery resting voltage is below
+    // FWD_THR_CUTOFF_V (if set), to preserve battery life for the electronics
+    // and actuators. Only applies when the battery monitor is working and the
+    // current mode does auto-throttle.
+    if (is_positive(batt_voltage_throttle_cutoff) &&
+        plane.control_mode->does_auto_throttle() && AP::battery().healthy(batt_idx) &&
+        (AP::battery().voltage_resting_estimate(batt_idx) < batt_voltage_throttle_cutoff)) {
+        min_throttle = 0;
+        max_throttle = 0;
+
+        return;
+    }
+
     // return if not enabled
     if (!enabled) {
         return;