Plane: re-implement MIXING_OFFSET

this was lost in the conversion of SRV_Channels

ArduPlane/Parameters.cpp

@@ -710,8 +710,8 @@ const AP_Param::Info Plane::var_info[] = {
     // @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: d%
-    // @Range: -1000 1000
+    // @Units: %
+    // @Range: -100 100
     // @User: User
     GSCALAR(dspoiler_rud_rate,      "DSPOILR_RUD_RATE",  DSPOILR_RUD_RATE_DEFAULT),
 

ArduPlane/servos.cpp

@@ -148,6 +148,14 @@ void Plane::channel_function_mixer(SRV_Channel::Aux_servo_function_t func1_in, S
     // reversal as needed
     float in1 = SRV_Channels::get_output_scaled(func1_in);
     float in2 = SRV_Channels::get_output_scaled(func2_in);
+
+    // apply MIXING_OFFSET to input channels
+    if (g.mixing_offset < 0) {
+        in2 *= (100 - g.mixing_offset) * 0.01;
+    } else if (g.mixing_offset > 0) {
+        in1 *= (100 + g.mixing_offset) * 0.01;
+    }
+    
     float out1 = constrain_float((in2 - in1) * g.mixing_gain, -4500, 4500);
     float out2 = constrain_float((in2 + in1) * g.mixing_gain, -4500, 4500);
     SRV_Channels::set_output_scaled(func1_out, out1);
@@ -191,7 +199,8 @@ void Plane::dspoiler_update(void)
     }
     float elevon_left = SRV_Channels::get_output_scaled(SRV_Channel::k_elevon_left);
     float elevon_right = SRV_Channels::get_output_scaled(SRV_Channel::k_elevon_right);
-    float rudder = SRV_Channels::get_output_scaled(SRV_Channel::k_rudder);
+    float rudder_rate = g.dspoiler_rud_rate * 0.01f;
+    float rudder = SRV_Channels::get_output_scaled(SRV_Channel::k_rudder) * rudder_rate;
     float dspoiler1_left = elevon_left;
     float dspoiler2_left = elevon_left;
     float dspoiler1_right = elevon_right;