Track the output gain instead of amplitude so the measured values are

consistent if the settings are changed afterwards.

flight/Modules/Autotune/autotune.c

@@ -254,16 +254,13 @@ static void update_stabilization_settings()
 	const float gain_ratio_p = 1.0f / 5.0f;
 	const float zero_ratio_p = 1.0f / 5.0f;
 
-	float input = relaySettings.Amplitude * 4.0f / M_PI;      // amplitude of input (fundamental component of fourier series for the square wave)
-
 	// For now just run over roll and pitch
 	for (uint i = 0; i < 2; i++) {
-		float output = relayTuning.Amplitude[i];               // amplitude of sinusoidal oscillation in output
 		float wu = 1000.0f * 2 * M_PI / relayTuning.Period[i]; // ultimate freq = output osc freq (rad/s)
 
 		float wc = wu * gain_ratio_r;      // target openloop crossover frequency (rad/s)
 		float zc = wc * zero_ratio_r;      // controller zero location (rad/s)
-		float kpu = input / output;        // ultimate gain, i.e. the proportional gain for instablity
+		float kpu = 4.0f / M_PI / relayTuning.Gain[i];  // ultimate gain, i.e. the proportional gain for instablity
 		float kp = kpu * gain_ratio_r;     // proportional gain
 		float ki = zc * kp;                // integral gain
 

shared/uavobjectdefinition/relaytuning.xml

@@ -2,7 +2,7 @@
     <object name="RelayTuning" singleinstance="true" settings="false">
         <description>The input to the relay tuning.</description>
 	<field name="Period" units="ms" type="float" elementnames="Roll,Pitch,Yaw"/>
-	<field name="Amplitude" units="deg/s" type="float" elementnames="Roll,Pitch,Yaw"/>
+	<field name="Gain" units="(deg/s)/output" type="float" elementnames="Roll,Pitch,Yaw"/>
         <access gcs="readwrite" flight="readwrite"/>
         <telemetrygcs acked="false" updatemode="manual" period="0"/>
         <telemetryflight acked="false" updatemode="periodic" period="1000"/>