From 171da3dd08e3c70fa8b00e8355da504b8c7e9330 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Tue, 5 Mar 2024 08:04:53 +1100
Subject: [PATCH] AP_Motors: smoother ramp down in output_motor_mask

stop changing motors outside the given mask in output_motor_mask,
which gives smoother ramp down in tilt quadplanes when we are
transitioning to forward flight

thanks to Pete for the suggestion
---
 libraries/AP_Motors/AP_MotorsMulticopter.cpp | 11 ++++++-----
 libraries/AP_Motors/AP_MotorsTri.cpp         |  2 +-
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/libraries/AP_Motors/AP_MotorsMulticopter.cpp b/libraries/AP_Motors/AP_MotorsMulticopter.cpp
index e4a75ef330..cece6dd8cd 100644
--- a/libraries/AP_Motors/AP_MotorsMulticopter.cpp
+++ b/libraries/AP_Motors/AP_MotorsMulticopter.cpp
@@ -733,8 +733,8 @@ void AP_MotorsMulticopter::output_motor_mask(float thrust, uint16_t mask, float
     _motor_mask_override = mask;
 
     for (uint8_t i = 0; i < AP_MOTORS_MAX_NUM_MOTORS; i++) {
-        if (motor_enabled[i]) {
-            if ((mask & (1U << i)) && armed() && get_interlock()) {
+        if (motor_enabled[i] && (mask & (1U << i)) != 0) {
+            if (armed() && get_interlock()) {
                 /*
                  apply rudder mixing differential thrust
                  copter frame roll is plane frame yaw as this only
@@ -742,11 +742,12 @@ void AP_MotorsMulticopter::output_motor_mask(float thrust, uint16_t mask, float
                  */
                 float diff_thrust = get_roll_factor(i) * rudder_dt * 0.5f;
                 set_actuator_with_slew(_actuator[i], thrust + diff_thrust);
-                int16_t pwm_output = pwm_min + pwm_range * _actuator[i];
-                rc_write(i, pwm_output);
             } else {
-                rc_write(i, pwm_min);
+                // zero throttle
+                _actuator[i] = 0.0;
             }
+            int16_t pwm_output = pwm_min + pwm_range * _actuator[i];
+            rc_write(i, pwm_output);
         }
     }
 }
diff --git a/libraries/AP_Motors/AP_MotorsTri.cpp b/libraries/AP_Motors/AP_MotorsTri.cpp
index c109ade093..ab566944ae 100644
--- a/libraries/AP_Motors/AP_MotorsTri.cpp
+++ b/libraries/AP_Motors/AP_MotorsTri.cpp
@@ -92,7 +92,7 @@ void AP_MotorsTri::output_to_motors()
             // sends minimum values out to the motors
             for (uint8_t i = 0; i < AP_MOTORS_MAX_NUM_MOTORS; i++) {
                 if (motor_enabled_mask(i)) {
-                    rc_write(AP_MOTORS_MOT_1+i, output_to_pwm(0));
+                    _actuator[AP_MOTORS_MOT_1+i] = 0;
                 }
             }
             rc_write_angle(AP_MOTORS_CH_TRI_YAW, 0);