Change temperature curve to cubic

fantemp/controller.cpp

@@ -24,7 +24,14 @@ void Controller::callback()
 
 uint8_t Controller::mapTemperature(double temperature)
 {
-	double fanSpeed = (10 * temperature - 200) / 3;
+	[[maybe_unused]] constexpr auto linearCurve = [](double x) { return (10 * x - 200) / 3; };
+	constexpr auto cubicCurve = [](double x) {
+		if (x < 20)
+			return 0.0;
+		return 0.002246 * x * x * x - 0.09 * x * x + 0.91 * x;
+	};
+
+	double fanSpeed = cubicCurve(temperature);
 	return clamp<uint8_t>(fanSpeed, 0, 100);
 }