AP_HAL_PX4: ESC scaling

libraries/AP_HAL_PX4/RCOutput.h

@@ -29,6 +29,9 @@ public:
         _esc_pwm_min = min_pwm;
         _esc_pwm_max = max_pwm;
     }
+    float    scale_esc_to_unity(uint16_t pwm) override {
+        return 2.0 * ((float) pwm - _esc_pwm_min) / (_esc_pwm_max - _esc_pwm_min) - 1.0;
+    }
     void cork();
     void push();