AC_AttitudeControl: Add minimum angle limit for get_althold_lean_angle_max

libraries/AC_AttitudeControl/AC_AttitudeControl.cpp

@@ -903,7 +903,7 @@ void AC_AttitudeControl::accel_limiting(bool enable_limits)
 float AC_AttitudeControl::get_althold_lean_angle_max() const
 {
     // convert to centi-degrees for public interface
-    return ToDeg(_althold_lean_angle_max) * 100.0f;
+    return MAX(ToDeg(_althold_lean_angle_max), AC_ATTITUDE_CONTROL_ANGLE_LIMIT_MIN) * 100.0f;
 }
 
 // Proportional controller with piecewise sqrt sections to constrain second derivative

libraries/AC_AttitudeControl/AC_AttitudeControl.h

@@ -34,6 +34,7 @@
 
 #define AC_ATTITUDE_CONTROL_ANGLE_LIMIT_TC_DEFAULT      1.0f    // Time constant used to limit lean angle so that vehicle does not lose altitude
 #define AC_ATTITUDE_CONTROL_ANGLE_LIMIT_THROTTLE_MAX    0.8f    // Max throttle used to limit lean angle so that vehicle does not lose altitude
+#define AC_ATTITUDE_CONTROL_ANGLE_LIMIT_MIN             10.0f   // Min lean angle so that vehicle can maintain limited control
 
 #define AC_ATTITUDE_CONTROL_MIN_DEFAULT                 0.1f    // minimum throttle mix default
 #define AC_ATTITUDE_CONTROL_MAN_DEFAULT                 0.5f    // manual throttle mix default