allow configuration of motor arming condition

This allows the user to configure their own motor arming condition in
APM_Config.h. For example, the user could set it up for MODE1
transmitters, by using:

 #define MOTOR_ARM_CONDITION (g.rc_3.control_in == 0 && g.rc_1.control_in > 2700)
 #define MOTOR_DISARM_CONDITION (g.rc_3.control_in == 0 && g.rc_1.control_in < -2700)

You could also set it up to use the "throttle cut" switch on a
transmitter, by mapping that to a spare channel.

The default (throttle minimum and maximum/minimum yaw) is the same as
it was before

This patch also adds reporting of motor arming to the GCS, which can
be useful for testing.

git-svn-id: https://arducopter.googlecode.com/svn/trunk@1802 f9c3cf11-9bcb-44bc-f272-b75c42450872

ArduCopterMega/config.h

@@ -558,3 +558,16 @@
 #ifndef ALLOW_RC_OVERRIDE
 # define ALLOW_RC_OVERRIDE DISABLED
 #endif
+
+//////////////////////////////////////////////////////////////////////////////
+// Motor arming
+//
+// The default is for MODE2 setups. We wait for throttle to reach
+// zero, and rudder to be at maximum extent.
+#ifndef MOTOR_ARM_CONDITION
+# define MOTOR_ARM_CONDITION (g.rc_3.control_in == 0 && g.rc_4.control_in > 2700)
+#endif
+
+#ifndef MOTOR_DISARM_CONDITION
+# define MOTOR_DISARM_CONDITION (g.rc_3.control_in == 0 && g.rc_4.control_in < -2700)
+#endif

ArduCopterMega/motors.pde

@@ -6,25 +6,29 @@
 void arm_motors()
 {
 	static byte arming_counter;
-
+	// Serial.printf("rc3: %u  rc4: %u\n", g.rc_3.control_in, g.rc_4.control_in);
 	// Arm motor output : Throttle down and full yaw right for more than 2 seconds
-	if (g.rc_3.control_in == 0){
+	if (MOTOR_ARM_CONDITION) {
-		if (g.rc_4.control_in > 2700) {
 		if (arming_counter > ARM_DELAY) {
+			if (!motor_armed) {
+				gcs.send_text(SEVERITY_MEDIUM, "Arming motors");
+			}
 			motor_armed = true;
 		} else{
 			arming_counter++;
 		}
-		}else if (g.rc_4.control_in < -2700) {
+	} else if (MOTOR_DISARM_CONDITION) {
 		if (arming_counter > DISARM_DELAY){
+			if (motor_armed) {
+				gcs.send_text(SEVERITY_MEDIUM, "Dis-arming motors");
+			}
 			motor_armed = false;
-			}else{
+		} else {
 			arming_counter++;
 		}
-		}else{
+	} else {
 		arming_counter = 0;
 	}
-	}
 }