Refactor arming logic

Arm and disarm with gestures only: left stick right/down for arming, left/down for disarming.
Remove arming switch as it complicates arming gestures logic.
Remove MAV_CTRL_SCALE parameter as it complicates arming gestures logic, advise to decrease TILT_MAX when controlling with a smartphone.
Put some minimal thrust to motors to indicate armed state.
Rename build article to usage article, add flight instructions.

flix/cli.ino

@@ -14,6 +14,7 @@ extern double t;
 extern uint16_t channels[16];
 extern float controlRoll, controlPitch, controlThrottle, controlYaw, controlMode;
 extern int mode;
+extern bool armed;
 
 const char* motd =
 "\nWelcome to\n"
@@ -33,6 +34,8 @@ const char* motd =
 "ps - show pitch/roll/yaw\n"
 "psq - show attitude quaternion\n"
 "imu - show IMU data\n"
+"arm - arm the drone\n"
+"disarm - disarm the drone\n"
 "stab / acro - set mode\n"
 "rc - show RC data\n"
 "mot - show motor output\n"
@@ -109,6 +112,10 @@ void doCommand(String str, bool echo = false) {
 		printIMUInfo();
 		printIMUCalibration();
 		print("landed: %d\n", landed);
+	} else if (command == "arm") {
+		armed = true;
+	} else if (command == "disarm") {
+		armed = false;
 	} else if (command == "stab") {
 		mode = STAB;
 	} else if (command == "acro") {
@@ -121,6 +128,7 @@ void doCommand(String str, bool echo = false) {
 		print("\nroll: %g pitch: %g yaw: %g throttle: %g mode: %g\n",
 			controlRoll, controlPitch, controlYaw, controlThrottle, controlMode);
 		print("mode: %s\n", getModeName());
+		print("armed: %d\n", armed);
 	} else if (command == "mot") {
 		print("front-right %g front-left %g rear-right %g rear-left %g\n",
 			motors[MOTOR_FRONT_RIGHT], motors[MOTOR_FRONT_LEFT], motors[MOTOR_REAR_RIGHT], motors[MOTOR_REAR_LEFT]);

flix/control.ino

@@ -9,6 +9,7 @@
 #include "lpf.h"
 #include "util.h"
 
+#define ARMED_THRUST 0.1 // thrust to indicate armed state
 #define PITCHRATE_P 0.05
 #define PITCHRATE_I 0.2
 #define PITCHRATE_D 0.001
@@ -54,7 +55,7 @@ Vector torqueTarget;
 float thrustTarget;
 
 extern const int MOTOR_REAR_LEFT, MOTOR_REAR_RIGHT, MOTOR_FRONT_RIGHT, MOTOR_FRONT_LEFT;
-extern float controlRoll, controlPitch, controlThrottle, controlYaw, controlArmed, controlMode;
+extern float controlRoll, controlPitch, controlThrottle, controlYaw, controlMode;
 
 void control() {
 	interpretControls();
@@ -65,14 +66,14 @@ void control() {
 }
 
 void interpretControls() {
-	armed = controlThrottle >= 0.05;
-	if (controlArmed < 0.5) armed = false;
-
 	// NOTE: put ACRO or MANUAL modes there if you want to use them
 	if (controlMode < 0.25) mode = STAB;
 	if (controlMode < 0.75) mode = STAB;
 	if (controlMode > 0.75) mode = STAB;
 
+	if (controlThrottle < 0.05 && controlYaw > 0.95) armed = true; // arm gesture
+	if (controlThrottle < 0.05 && controlYaw < -0.95) armed = false; // disarm gesture
+
 	thrustTarget = controlThrottle;
 
 	if (mode == STAB) {
@@ -137,8 +138,17 @@ void controlRates() {
 void controlTorque() {
 	if (!torqueTarget.valid()) return; // skip torque control
 
-	if (!armed || thrustTarget < 0.05) {
-		memset(motors, 0, sizeof(motors)); // stop motors if no thrust
+	if (!armed) {
+		memset(motors, 0, sizeof(motors)); // stop motors if disarmed
+		return;
+	}
+
+	if (thrustTarget < 0.05) {
+		// minimal thrust to indicate armed state
+		motors[0] = ARMED_THRUST;
+		motors[1] = ARMED_THRUST;
+		motors[2] = ARMED_THRUST;
+		motors[3] = ARMED_THRUST;
 		return;
 	}
 

flix/failsafe.ino

@@ -10,19 +10,9 @@ extern double controlTime;
 extern float controlRoll, controlPitch, controlThrottle, controlYaw;
 
 void failsafe() {
-	armingFailsafe();
 	rcLossFailsafe();
 }
 
-// Prevent arming without zero throttle input
-void armingFailsafe() {
-	static double zeroThrottleTime;
-	static double armingTime;
-	if (!armed) armingTime = t; // stores the last time when the drone was disarmed, therefore contains arming time
-	if (controlTime > 0 && controlThrottle < 0.05) zeroThrottleTime = controlTime;
-	if (armingTime - zeroThrottleTime > 0.1) armed = false; // prevent arming if there was no zero throttle for 0.1 sec
-}
-
 // RC loss failsafe
 void rcLossFailsafe() {
 	if (t - controlTime > RC_LOSS_TIMEOUT) {
@@ -37,5 +27,8 @@ void descend() {
 	controlPitch = 0;
 	controlYaw = 0;
 	controlThrottle -= dt / DESCEND_TIME;
-	if (controlThrottle < 0) controlThrottle = 0;
+	if (controlThrottle < 0) {
+		armed = false;
+		controlThrottle = 0;
+	}
 }

flix/flix.ino

@@ -13,7 +13,7 @@
 double t = NAN; // current step time, s
 float dt; // time delta from previous step, s
 float controlRoll, controlPitch, controlYaw, controlThrottle; // pilot's inputs, range [-1, 1]
-float controlArmed = NAN, controlMode = NAN;
+float controlMode = NAN;
 Vector gyro; // gyroscope data
 Vector acc; // accelerometer data, m/s/s
 Vector rates; // filtered angular rates, rad/s

flix/mavlink.ino

@@ -12,11 +12,10 @@
 #define PERIOD_FAST 0.1
 #define MAVLINK_CONTROL_YAW_DEAD_ZONE 0.1f
 
-float mavlinkControlScale = 0.7;
 String mavlinkPrintBuffer;
 
 extern double controlTime;
-extern float controlRoll, controlPitch, controlThrottle, controlYaw, controlArmed, controlMode;
+extern float controlRoll, controlPitch, controlThrottle, controlYaw, controlMode;
 
 void processMavlink() {
 	sendMavlink();
@@ -99,11 +98,10 @@ void handleMavlink(const void *_msg) {
 		if (m.target && m.target != SYSTEM_ID) return; // 0 is broadcast
 
 		controlThrottle = m.z / 1000.0f;
-		controlPitch = m.x / 1000.0f * mavlinkControlScale;
-		controlRoll = m.y / 1000.0f * mavlinkControlScale;
-		controlYaw = m.r / 1000.0f * mavlinkControlScale;
+		controlPitch = m.x / 1000.0f;
+		controlRoll = m.y / 1000.0f;
+		controlYaw = m.r / 1000.0f;
 		controlMode = NAN;
-		controlArmed = NAN;
 		controlTime = t;
 
 		if (abs(controlYaw) < MAVLINK_CONTROL_YAW_DEAD_ZONE) controlYaw = 0;

flix/parameters.ino

@@ -70,12 +70,7 @@ Parameter parameters[] = {
 	{"RC_PITCH", &pitchChannel},
 	{"RC_THROTTLE", &throttleChannel},
 	{"RC_YAW", &yawChannel},
-	{"RC_ARMED", &armedChannel},
 	{"RC_MODE", &modeChannel},
-#if WIFI_ENABLED
-	// MAVLink
-	{"MAV_CTRL_SCALE", &mavlinkControlScale},
-#endif
 };
 
 void setupParameters() {

flix/rc.ino

@@ -14,7 +14,7 @@ float channelZero[16]; // calibration zero values
 float channelMax[16]; // calibration max values
 
 // Channels mapping (using float to store in parameters):
-float rollChannel = NAN, pitchChannel = NAN, throttleChannel = NAN, yawChannel = NAN, armedChannel = NAN, modeChannel = NAN;
+float rollChannel = NAN, pitchChannel = NAN, throttleChannel = NAN, yawChannel = NAN, modeChannel = NAN;
 
 void setupRC() {
 	print("Setup RC\n");
@@ -42,7 +42,6 @@ void normalizeRC() {
 	controlPitch = pitchChannel >= 0 ? controls[(int)pitchChannel] : NAN;
 	controlYaw = yawChannel >= 0 ? controls[(int)yawChannel] : NAN;
 	controlThrottle = throttleChannel >= 0 ? controls[(int)throttleChannel] : NAN;
-	controlArmed = armedChannel >= 0 ? controls[(int)armedChannel] : NAN;
 	controlMode = modeChannel >= 0 ? controls[(int)modeChannel] : NAN;
 }
 
@@ -58,8 +57,7 @@ void calibrateRC() {
 	calibrateRCChannel(&yawChannel, center, max, "5/9 Move sticks [3 sec]\n...     ...\n..o     .o.\n...     ...\n");
 	calibrateRCChannel(&pitchChannel, zero, max, "6/9 Move sticks [3 sec]\n...     .o.\n...     ...\n.o.     ...\n");
 	calibrateRCChannel(&rollChannel, zero, max, "7/9 Move sticks [3 sec]\n...     ...\n...     ..o\n.o.     ...\n");
-	calibrateRCChannel(&armedChannel, zero, max, "8/9 Switch to armed [3 sec]\n");
-	calibrateRCChannel(&modeChannel, zero, max, "9/9 Disarm and switch mode to max [3 sec]\n");
+	calibrateRCChannel(&modeChannel, zero, max, "9/9 Put mode switch to max [3 sec]\n");
 	printRCCalibration();
 }
 
@@ -94,6 +92,5 @@ void printRCCalibration() {
 	print("Pitch     %-7g%-7g%-7g\n", pitchChannel, pitchChannel >= 0 ? channelZero[(int)pitchChannel] : NAN, pitchChannel >= 0 ? channelMax[(int)pitchChannel] : NAN);
 	print("Yaw       %-7g%-7g%-7g\n", yawChannel, yawChannel >= 0 ? channelZero[(int)yawChannel] : NAN, yawChannel >= 0 ? channelMax[(int)yawChannel] : NAN);
 	print("Throttle  %-7g%-7g%-7g\n", throttleChannel, throttleChannel >= 0 ? channelZero[(int)throttleChannel] : NAN, throttleChannel >= 0 ? channelMax[(int)throttleChannel] : NAN);
-	print("Armed     %-7g%-7g%-7g\n", armedChannel, armedChannel >= 0 ? channelZero[(int)armedChannel] : NAN, armedChannel >= 0 ? channelMax[(int)armedChannel] : NAN);
 	print("Mode      %-7g%-7g%-7g\n", modeChannel, modeChannel >= 0 ? channelZero[(int)modeChannel] : NAN, modeChannel >= 0 ? channelMax[(int)modeChannel] : NAN);
 }