Differential spoilers support, elevon offset

Fixed differential spoilers support, added elevon offset
See PR #2935

ArduPlane/Attitude.cpp

@@ -680,6 +680,15 @@ void Plane::channel_output_mixer(uint8_t mixing_type, int16_t & chan1_out, int16
     c1 = chan1_out - 1500;
     c2 = chan2_out - 1500;
 
+    // apply MIXING_OFFSET to input channels using long-integer version
+    //  of formula:  x = x * (g.mixing_offset/100.0 + 1.0)
+    //  -100 => 2x on 'c1', 100 => 2x on 'c2'
+    if (g.mixing_offset < 0) {
+        c1 = (int16_t)(((int32_t)c1) * (-g.mixing_offset+100) / 100);
+    } else if (g.mixing_offset > 0) {
+        c2 = (int16_t)(((int32_t)c2) * (g.mixing_offset+100) / 100);
+    }
+
     v1 = (c1 - c2) * g.mixing_gain;
     v2 = (c1 + c2) * g.mixing_gain;
 
@@ -868,12 +877,6 @@ void Plane::set_servos(void)
         RC_Channel_aux::copy_radio_in_out(RC_Channel_aux::k_aileron_with_input);
         RC_Channel_aux::copy_radio_in_out(RC_Channel_aux::k_elevator_with_input);
 
-        if (g.mix_mode == 0 && g.elevon_output == MIXING_DISABLED) {
-            // set any differential spoilers to follow the elevons in
-            // manual mode. 
-            RC_Channel_aux::set_radio(RC_Channel_aux::k_dspoiler1, channel_roll->get_radio_out());
-            RC_Channel_aux::set_radio(RC_Channel_aux::k_dspoiler2, channel_pitch->get_radio_out());
-        }
     } else {
         if (g.mix_mode == 0) {
             // both types of secondary aileron are slaved to the roll servo out
@@ -1120,6 +1123,43 @@ void Plane::set_servos(void)
         channel_output_mixer(g.vtail_output, channel_pitch, channel_rudder);
     } else if (g.elevon_output != MIXING_DISABLED) {
         channel_output_mixer(g.elevon_output, channel_pitch, channel_roll);
+        // if (both) differential spoilers setup then apply rudder
+        //  control into splitting the two elevons on the side of
+        //  the aircraft where we want to induce additional drag:
+        if (RC_Channel_aux::function_assigned(RC_Channel_aux::k_dspoiler1) &&
+            RC_Channel_aux::function_assigned(RC_Channel_aux::k_dspoiler2)) {
+            int16_t ch3 = channel_roll->get_radio_out();    //diff spoiler 1
+            int16_t ch4 = channel_pitch->get_radio_out();   //diff spoiler 2
+            // convert rudder-servo output (-4500 to 4500) to PWM offset
+            //  value (-500 to 500) and multiply by DSPOILR_RUD_RATE/100
+            //  (rudder->servo_out * 500 / SERVO_MAX * dspoiler_rud_rate/100):
+            int16_t ruddVal = (int16_t)((int32_t)(channel_rudder->get_servo_out()) *
+                                        g.dspoiler_rud_rate / (SERVO_MAX/5));
+            if (ruddVal != 0) {   //if nonzero rudder then apply to spoilers
+                int16_t ch1 = ch3;          //elevon 1
+                int16_t ch2 = ch4;          //elevon 2
+                if (ruddVal > 0) {     //apply rudder to right or left side
+                    ch1 += ruddVal;
+                    ch3 -= ruddVal;
+                } else {
+                    ch2 += ruddVal;
+                    ch4 -= ruddVal;
+                }
+                // change elevon 1 & 2 positions; constrain min/max:
+                channel_roll->set_radio_out(constrain_int16(ch1, 900, 2100));
+                channel_pitch->set_radio_out(constrain_int16(ch2, 900, 2100));
+                // constrain min/max for intermediate dspoiler positions:
+                ch3 = constrain_int16(ch3, 900, 2100);
+                ch4 = constrain_int16(ch4, 900, 2100);
+            }
+            // set positions of differential spoilers (convert PWM
+            //  900-2100 range to servo output (-4500 to 4500)
+            //  and use function that supports rev/min/max/trim):
+            RC_Channel_aux::set_servo_out_for(RC_Channel_aux::k_dspoiler1,
+                                              (ch3-(int16_t)1500) * (int16_t)(SERVO_MAX/300) / (int16_t)2);
+            RC_Channel_aux::set_servo_out_for(RC_Channel_aux::k_dspoiler2,
+                                              (ch4-(int16_t)1500) * (int16_t)(SERVO_MAX/300) / (int16_t)2);
+        }
     }
 
     if (!arming.is_armed()) {

ArduPlane/Parameters.cpp

@@ -863,6 +863,22 @@ const AP_Param::Info Plane::var_info[] = {
     // @User: User
     GSCALAR(rudder_only,             "RUDDER_ONLY",  0),
 
+    // @Param: MIXING_OFFSET
+    // @DisplayName: Mixing Offset
+    // @Description: The offset for the Vtail and elevon output mixers, as a percentage. This can be used in combination with MIXING_GAIN to configure how the control surfaces respond to input. The response to aileron or elevator input can be increased by setting this parameter to a positive or negative value. A common usage is to enter a positive value to increase the aileron response of the elevons of a flying wing. The default value of zero will leave the aileron-input response equal to the elevator-input response.
+    // @Units: percent
+    // @Range: -1000 1000
+    // @User: User
+    GSCALAR(mixing_offset,          "MIXING_OFFSET",  0),
+
+    // @Param: DSPOILR_RUD_RATE
+    // @DisplayName: Differential spoilers rudder rate
+    // @Description: Sets the amount of deflection that the rudder output will apply to the differential spoilers, as a percentage. The default value of 100 results in full rudder applying full deflection. A value of 0 will result in the differential spoilers exactly following the elevons (no rudder effect).
+    // @Units: percent
+    // @Range: -1000 1000
+    // @User: User
+    GSCALAR(dspoiler_rud_rate,      "DSPOILR_RUD_RATE",  DSPOILR_RUD_RATE_DEFAULT),
+
     // @Param: SYS_NUM_RESETS
     // @DisplayName: Num Resets
     // @Description: Number of APM board resets

ArduPlane/Parameters.h

@@ -341,6 +341,9 @@ public:
         k_param_pidNavPitchAltitude, // unused
         k_param_pidWheelSteer, // unused
 
+        k_param_mixing_offset,
+        k_param_dspoiler_rud_rate,
+
         k_param_DataFlash = 253, // Logging Group
 
         // 254,255: reserved
@@ -463,6 +466,8 @@ public:
     AP_Int8 reverse_elevons;
     AP_Int8 reverse_ch1_elevon;
     AP_Int8 reverse_ch2_elevon;
+    AP_Int16 mixing_offset;
+    AP_Int16 dspoiler_rud_rate;
     AP_Int16 num_resets;
     AP_Int32 log_bitmask;
     AP_Int8 reset_switch_chan;

ArduPlane/config.h

@@ -220,6 +220,10 @@
  # define ELEVON_CH2_REVERSE     DISABLED
 #endif
 
+#ifndef DSPOILR_RUD_RATE_DEFAULT
+ #define DSPOILR_RUD_RATE_DEFAULT 100
+#endif
+
 //////////////////////////////////////////////////////////////////////////////
 // CAMERA TRIGGER AND CONTROL
 //