PWM: Add servo center setting & asymetric deflection (#25897)

Add PWM_*_CENTERx for each servo.
Use a bilinear transform to map actuator_servos to PWM signals.

This solution only works for PWM based servos. Other types of servos are not affected.

* PWM: Add servo trim option

* PWM: Improve documentation of PWM trim feature

* PWM: cleaner clamping and docs typo

* update documentation & safety

* add migration formula

* rename param from trim to center

* docs with center instead of trim

* move clamping and reorder values

* improve documentation

* adress failing range check

* improve documentation

* CA: add event for setting CENTER with TRIM

Signed-off-by: Silvan <silvan@auterion.com>

---------

Signed-off-by: Silvan <silvan@auterion.com>
Co-authored-by: Silvan <silvan@auterion.com>

src/modules/control_allocator/VehicleActuatorEffectiveness/ActuatorEffectivenessControlSurfaces.cpp

@@ -32,6 +32,7 @@
  ****************************************************************************/
 
 #include <px4_platform_common/log.h>
+#include <px4_platform_common/events.h>
 
 #include "ActuatorEffectivenessControlSurfaces.hpp"
 
@@ -74,6 +75,40 @@ void ActuatorEffectivenessControlSurfaces::updateParams()
 		return;
 	}
 
+	// Helper to check if a PWM center parameter is enabled, and clamp it to valid range
+	auto check_pwm_center = [](const char *prefix, int channel) -> bool {
+		char param_name[20];
+		snprintf(param_name, sizeof(param_name), "%s_CENT%d", prefix, channel);
+		param_t param = param_find(param_name);
+
+		if (param != PARAM_INVALID)
+		{
+			int32_t value;
+
+			if (param_get(param, &value) == PX4_OK && value != -1) {
+				// Clamp PWM center to valid range [800, 2200]
+				if (value < 800 || value > 2200) {
+					int32_t clamped = (value < 800) ? 800 : 2200;
+					PX4_WARN("%s_CENT%d (%d) out of range, clamping to %d", prefix, channel, (int)value, (int)clamped);
+					param_set(param, &clamped);
+				}
+
+				return true;
+			}
+		}
+
+		return false;
+	};
+
+	// Check if any PWM_MAIN or PWM_AUX center is configured
+	bool pwm_center_set = false;
+
+	for (int i = 1; i <= 8; i++) {
+		if (check_pwm_center("PWM_MAIN", i) || check_pwm_center("PWM_AUX", i)) {
+			pwm_center_set = true;
+		}
+	}
+
 	for (int i = 0; i < _count; i++) {
 		param_get(_param_handles[i].type, (int32_t *)&_params[i].type);
 
@@ -84,6 +119,20 @@ void ActuatorEffectivenessControlSurfaces::updateParams()
 		}
 
 		param_get(_param_handles[i].trim, &_params[i].trim);
+
+		// If PWM center is set and CA_SV_CS trim is non-zero, warn and reset to 0
+		if (pwm_center_set && fabsf(_params[i].trim) > FLT_EPSILON) {
+			/* EVENT
+			* @description Display warning in GCS when TRIM settings were present and now CENTER are set.
+			*/
+			events::send<uint8_t, float>(events::ID("control_surfaces_reset_trim"), events::Log::Warning,
+						     "CA_SV_CS{1}_TRIM ({2}) is reset to 0 as PWM CENTER is used", i, _params[i].trim);
+
+			_params[i].trim = 0.0f;
+			// Update the parameter storage
+			param_set(_param_handles[i].trim, &_params[i].trim);
+		}
+
 		param_get(_param_handles[i].scale_flap, &_params[i].scale_flap);
 		param_get(_param_handles[i].scale_spoiler, &_params[i].scale_spoiler);
 

src/modules/control_allocator/module.yaml

@@ -312,7 +312,11 @@ parameters:
         CA_SV_CS${i}_TRIM:
             description:
                 short: Control Surface ${i} trim
-                long: Can be used to add an offset to the servo control.
+                long: |
+                  Can be used to add an offset to the servo control.
+
+                  NOTE: Do not use for PWM servos. Use the PWM CENTER parameters instead (e.g., PWM_MAIN_CENT, PWM_AUX_CENT) instead.
+                  This parameter can only be set if all PWM Center parameters are set to default.
             type: float
             decimal: 2
             min: -1.0