update documentation & safety

docs/en/config/actuators.md

@@ -535,7 +535,27 @@ If you're using PWM servos, PWM50 is far more common.
 If a high rate servo is _really_ needed, DShot offers better value.
 :::
 
-#### Control surfaces that move both directions about a neutral point
+##### PWM: Control surfaces that move both directions about a neutral point
+
+To facilitate setting the neutral point of the servos, a bilinear curve function can be defined using the following parameters `PWM_MAIM_TRIMx` / `PWM_AUX_TRIMx` for each servo. This allows for unequal deflections in the positive and negative direction:
+![Asymetric Servo Deflections](../../assets/config/actuators/servo_pwm_trim.png)
+
+To set this up:
+
+1. Set all surface `Trim` to `0.00` for all surfaces:
+
+     ![PWM Trimming](../../assets/config/actuators/trim_GS.png)
+
+1. Set the `PWM_MAIN_TRIMx` / `PWM_AUX_TRIMx` value so that the surface will stay at the neutral position.
+This is usually around `1500` for PWM servos (near the center of the servo range).
+
+![Control Surface Trimming](../../assets/config/actuators/control_surface_trim.png)
+
+2. Gradualy increase the `Maximum` for each servo, while checking the deflection with the sliders or manual input with [`COM_PREARM_MODE`](../advanced_config/parameter_reference.md#COM_PREARM_MODE) parameter to `Always` until the desired deflection is reached.
+3. Gradualy decrease the `Minimum` for each servo, until the desired deflection is reached.
+4. Set `Disarmed` value to the desired value. It is usually desirable to have it the same as the `Trim` value.
+
+#### Non-PWM: Control surfaces that move both directions about a neutral point
 
 Control surfaces that move either direction around a neutral point include: ailerons, elevons, V-tails, A-tails, and rudders.
 
@@ -575,27 +595,7 @@ Another way to test without using the sliders would be to set the [`COM_PREARM_M
 
 :::
 
-##### Split Servo Deflections
 
-::: info
-This method is experimental, but much faster.
-
-:::
-To facilitate setting the neutral point of the servos, a bilinear curve function can be defined using the following parameters `PWM_MAIM_TRIMx` / `PWM_AUX_TRIMx` for each servo. This allows for unequal deflections in the positive and negative direction:
-![Split Servo Deflections](../../assets/config/actuators/servo_pwm_trim.png)
-
-To set this up:
-
-1. Set all surface `Trim` to `0.00` for all surfaces:
-
-     ![Control Surface Trimming](../../assets/config/actuators/control_surface_trim.png)
-
-1. Set `Minimum`, `Maximum`, `Trim` and `Disarm` value so that the surface will stay at neutral position approximately.
-This is usually around `1500` for PWM servos (near the centre of the servo range).
-
-2. Gradualy increase the `Maximum` for each servo, while checking the deflection with the sliders or manual input with [`COM_PREARM_MODE`](../advanced_config/parameter_reference.md#COM_PREARM_MODE) parameter to `Always` until the desired deflection is reached.
-3. Gradualy decrease the `Minimum` for each servo, until the desired deflection is reached.
-4. Set `PWM_MAIN_TRIMx` / `PWM_AUX_TRIMx` to the neutral point of each servo.
 
 #### Control surfaces that move from neutral to full deflection
 
@@ -616,6 +616,7 @@ One approach for setting these up is:
    - If the value was increased towards `Max`, then set `Max` to match `Disarmed`.
 4. The value that you did _not_ set to match `Disarmed` controls the maximum amount that the control surface can extend.
    Set the slider to the top of the control, then change the value (`Max` or `Min`) so that the control surface is fully extended when the slider is at top.
+5. (Only PWM servos) Set the `Trim` value to the middle between `Min` and `Max`.
 
 ::: info Special note for flaps
 In some vehicle builds, flaps may be configured such that both flaps are controlled from a single output.

src/lib/mixer_module/mixer_module.cpp

@@ -548,7 +548,8 @@ uint16_t MixingOutput::output_limit_calc_single(int i, float value) const
 	float output = _disarmed_value[i];
 
 	if (_function_assignment[i] >= OutputFunction::Servo1
-	    && _function_assignment[i] <= OutputFunction::ServoMax) {
+	    && _function_assignment[i] <= OutputFunction::ServoMax
+	    && _param_handles[i].trim != PARAM_INVALID) {
 
 		/* bi-linear interpolation */
 		if (value < 0.0f) {

src/modules/control_allocator/VehicleActuatorEffectiveness/ActuatorEffectivenessControlSurfaces.cpp

@@ -74,6 +74,27 @@ void ActuatorEffectivenessControlSurfaces::updateParams()
 		return;
 	}
 
+	// Helper to check if a PWM trim parameter is set to non-default value (1500 µs)
+	auto check_pwm_trim = [](const char *prefix, int channel) -> bool {
+		char param_name[20];
+		snprintf(param_name, sizeof(param_name), "%s_TRIM%d", prefix, channel);
+		param_t param = param_find(param_name);
+
+		if (param != PARAM_INVALID) {
+			int32_t value;
+			return (param_get(param, &value) == PX4_OK && value != 1500);
+		}
+
+		return false;
+	};
+
+	// Check if any PWM_MAIN or PWM_AUX trim is configured
+	bool pwm_trim_set = false;
+
+	for (int i = 1; i <= 8 && !pwm_trim_set; i++) {
+		pwm_trim_set = check_pwm_trim("PWM_MAIN", i) || check_pwm_trim("PWM_AUX", i);
+	}
+
 	for (int i = 0; i < _count; i++) {
 		param_get(_param_handles[i].type, (int32_t *)&_params[i].type);
 
@@ -84,6 +105,16 @@ void ActuatorEffectivenessControlSurfaces::updateParams()
 		}
 
 		param_get(_param_handles[i].trim, &_params[i].trim);
+
+		// If PWM trim is set and CA_SV_CS trim is non-zero, warn and reset to 0
+		if (pwm_trim_set && fabsf(_params[i].trim) > 0.001f) {
+			PX4_WARN("CA_SV_CS%d_TRIM (%.3f) should be 0 when PWM TRIM is used. Resetting to 0.",
+				 i, (double)_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 TRIM parameters instead (e.g., PWM_MAIN_TRIM, PWM_AUX_TRIM) instead.
+                  This parameter can only be set if all PWM Trim parameters are set to default.
             type: float
             decimal: 2
             min: -1.0