MultirotorMixer: hotfix [-1,1] scaling

After it was mistakenly rescaled in
26bac78#diff-899d35a48340c6065702d4fa77b70f0d
#15563

src/lib/mixer/MultirotorMixer/MultirotorMixer.cpp

@@ -93,7 +93,7 @@ MultirotorMixer::MultirotorMixer(ControlCallback control_cb, uintptr_t cb_handle
 	_tmp_array(new float[_rotor_count])
 {
 	for (unsigned i = 0; i < _rotor_count; ++i) {
-		_outputs_prev[i] = 0.f;
+		_outputs_prev[i] = -1.f;
 	}
 }
 
@@ -356,7 +356,7 @@ MultirotorMixer::mix(float *outputs, unsigned space)
 							_thrust_factor));
 		}
 
-		outputs[i] = math::constrain(outputs[i], 0.f, 1.f);
+		outputs[i] = math::constrain((2.f * outputs[i] - 1.f), -1.f, 1.f);
 	}
 
 	// Slew rate limiting and saturation checking
@@ -370,7 +370,7 @@ MultirotorMixer::mix(float *outputs, unsigned space)
 		// clipping if airmode==roll/pitch), since in all other cases thrust will
 		// be reduced or boosted and we can keep the integrators enabled, which
 		// leads to better tracking performance.
-		if (outputs[i] < 0.01f) {
+		if (outputs[i] < -0.99f) {
 			if (_airmode == Airmode::disabled) {
 				clipping_low_roll_pitch = true;
 				clipping_low_yaw = true;

src/lib/mixer/MultirotorMixer/test_mixer_multirotor.cpp

@@ -108,6 +108,11 @@ int main(int argc, char *argv[])
 			return -1;
 		}
 
+		// Account for MultirotorMixer outputing [-1,1] and python script [0,1]
+		for (unsigned i = 0; i < rotor_count; i++) {
+			actuator_outputs[i] = (actuator_outputs[i] + 1.f) * .5f;
+		}
+
 		// read expected outputs
 		count = 0;
 		float expected_output[output_max];