public void update(ref double[] servos, ArdupilotMega.GCSViews.Simulation.FGNetFDM fdm)
        {
            for (int i = 0; i < servos.Length; i++)
            {
                if (servos[i] <= 0.0)
                {
                    motor_speed[i] = 0;
                }
                else
                {
                    motor_speed[i] = scale_rc(i, (float)servos[i], 0.0f, 1.0f);
                    //servos[i] = motor_speed[i];
                }
            }
            double[] m = motor_speed;

            /*
             * roll = 0;
             * pitch = 0;
             * yaw = 0;
             * roll_rate = 0;
             * pitch_rate = 0;
             * yaw_rate = 0;
             */

            //            Console.WriteLine("\nin m {0:0.000000} {1:0.000000} {2:0.000000} {3:0.000000}", m[0], m[1], m[2], m[3]);
            //            Console.WriteLine("in vel {0:0.000000} {1:0.000000} {2:0.000000}", velocity.X, velocity.Y, velocity.Z);
            //Console.WriteLine("in r {0:0.000000} p {1:0.000000} y {2:0.000000}    - r {3:0.000000} p {4:0.000000} y {5:0.000000}", roll, pitch, yaw, roll_rate, pitch_rate, yaw_rate);


            //            m[0] *= 0.5;

            //# how much time has passed?
            DateTime t          = DateTime.Now;
            TimeSpan delta_time = t - last_time; // 0.02

            last_time = t;

            if (delta_time.TotalMilliseconds > 100) // somethings wrong / debug
            {
                delta_time = new TimeSpan(0, 0, 0, 0, 20);
            }

            // rotational acceleration, in degrees/s/s, in body frame
            double roll_accel  = 0.0;
            double pitch_accel = 0.0;
            double yaw_accel   = 0.0;
            double thrust      = 0.0;

            foreach (var i in range((self.motors.Length)))
            {
                roll_accel  += -5000.0 * sin(radians(self.motors[i].angle)) * m[i];
                pitch_accel += 5000.0 * cos(radians(self.motors[i].angle)) * m[i];
                if (self.motors[i].clockwise)
                {
                    yaw_accel -= m[i] * 400.0;
                }
                else
                {
                    yaw_accel += m[i] * 400.0;
                }
                thrust += m[i] * self.thrust_scale; // newtons
            }

            // rotational resistance
            roll_accel  -= (self.pDeg / self.terminal_rotation_rate) * 5000.0;
            pitch_accel -= (self.qDeg / self.terminal_rotation_rate) * 5000.0;
            yaw_accel   -= (self.rDeg / self.terminal_rotation_rate) * 400.0;

            //Console.WriteLine("roll {0} {1} {2}", roll_accel, roll_rate, roll);

            //# update rotational rates in body frame
            self.pDeg += roll_accel * delta_time.TotalSeconds;
            self.qDeg += pitch_accel * delta_time.TotalSeconds;
            self.rDeg += yaw_accel * delta_time.TotalSeconds;

            // Console.WriteLine("roll {0} {1} {2}", roll_accel, roll_rate, roll);

            // calculate rates in earth frame

            var answer = BodyRatesToEarthRates(self.roll, self.pitch, self.yaw,
                                               self.pDeg, self.qDeg, self.rDeg);

            self.roll_rate  = answer.Item1;
            self.pitch_rate = answer.Item2;
            self.yaw_rate   = answer.Item3;

            //self.roll_rate = pDeg;
            //self.pitch_rate = qDeg;
            //self.yaw_rate = rDeg;

            //# update rotation
            roll  += roll_rate * delta_time.TotalSeconds;
            pitch += pitch_rate * delta_time.TotalSeconds;
            yaw   += yaw_rate * delta_time.TotalSeconds;

            //            Console.WriteLine("roll {0} {1} {2}", roll_accel, roll_rate, roll);

            //Console.WriteLine("r {0:0.0} p {1:0.0} y {2:0.0}    - r {3:0.0} p {4:0.0} y {5:0.0}  ms {6:0.000}", roll, pitch, yaw, roll_rate, pitch_rate, yaw_rate, delta_time.TotalSeconds);

            //# air resistance
            Vector3d air_resistance = -velocity * (gravity / terminal_velocity);

            //# normalise rotations
            normalise();

            double accel = thrust / mass;

            //Console.WriteLine("in {0:0.000000} {1:0.000000} {2:0.000000} {3:0.000000}", roll, pitch, yaw, accel);

            Vector3d accel3D = RPY_to_XYZ(roll, pitch, yaw, accel);

            //Console.WriteLine("accel3D " + accel3D.X + " " + accel3D.Y + " " + accel3D.Z);
            accel3D += new Vector3d(0, 0, -gravity);
            accel3D += air_resistance;

            Random rand = new Random();

            //velocity.X += .02 + rand.NextDouble() * .03;
            //velocity.Y += .02 + rand.NextDouble() * .03;

            //# new velocity vector
            velocity  += accel3D * delta_time.TotalSeconds;
            this.accel = accel3D;

            //# new position vector
            old_position = new Vector3d(position);
            position    += velocity * delta_time.TotalSeconds;

            //            Console.WriteLine(fdm.agl + " "+ fdm.altitude);

            //Console.WriteLine("Z {0} halt {1}  < gl {2} fh {3}" ,position.Z , home_altitude , ground_level , frame_height);

            if (home_latitude == 0 || home_latitude > 90 || home_latitude < -90 || home_longitude == 0)
            {
                this.home_latitude  = fdm.latitude * rad2deg;
                this.home_longitude = fdm.longitude * rad2deg;
                this.home_altitude  = fdm.altitude * ft2m;
                this.ground_level   = this.home_altitude;

                this.altitude  = fdm.altitude * ft2m;
                this.latitude  = fdm.latitude * rad2deg;
                this.longitude = fdm.longitude * rad2deg;
            }

            //# constrain height to the ground
            if (position.Z + home_altitude < ground_level + frame_height)
            {
                if (old_position.Z + home_altitude > ground_level + frame_height)
                {
                    //                    Console.WriteLine("Hit ground at {0} m/s", (-velocity.Z));
                }
                velocity   = new Vector3d(0, 0, 0);
                roll_rate  = 0;
                pitch_rate = 0;
                yaw_rate   = 0;
                roll       = 0;
                pitch      = 0;
                position   = new Vector3d(position.X, position.Y,
                                          ground_level + frame_height - home_altitude + 0);
                // Console.WriteLine("here " + position.Z);
            }

            //# update lat/lon/altitude
            update_position();

            // send to apm
#if MAVLINK10
            ArdupilotMega.MAVLink.mavlink_gps_raw_int_t gps = new ArdupilotMega.MAVLink.mavlink_gps_raw_int_t();
#else
            ArdupilotMega.MAVLink.mavlink_gps_raw_t gps = new ArdupilotMega.MAVLink.mavlink_gps_raw_t();
#endif

            ArdupilotMega.MAVLink.mavlink_attitude_t att = new ArdupilotMega.MAVLink.mavlink_attitude_t();

            ArdupilotMega.MAVLink.mavlink_vfr_hud_t asp = new ArdupilotMega.MAVLink.mavlink_vfr_hud_t();

            att.roll       = (float)roll * deg2rad;
            att.pitch      = (float)pitch * deg2rad;
            att.yaw        = (float)yaw * deg2rad;
            att.rollspeed  = (float)roll_rate * deg2rad;
            att.pitchspeed = (float)pitch_rate * deg2rad;
            att.yawspeed   = (float)yaw_rate * deg2rad;

#if MAVLINK10
            gps.alt       = ((int)(altitude * 1000));
            gps.fix_type  = 3;
            gps.vel       = (ushort)(Math.Sqrt((velocity.X * velocity.X) + (velocity.Y * velocity.Y)) * 100);
            gps.cog       = (ushort)((((Math.Atan2(velocity.Y, velocity.X) * rad2deg) + 360) % 360) * 100);
            gps.lat       = (int)(latitude * 1.0e7);
            gps.lon       = (int)(longitude * 1.0e7);
            gps.time_usec = ((ulong)DateTime.Now.Ticks);

            asp.airspeed = gps.vel;
#else
            gps.alt      = ((float)(altitude));
            gps.fix_type = 3;

            gps.lat  = ((float)latitude);
            gps.lon  = ((float)longitude);
            gps.usec = ((ulong)DateTime.Now.Ticks);

            //Random rand = new Random();
            //gps.alt += (rand.Next(100) - 50) / 100.0f;
            //gps.lat += (float)((rand.NextDouble() - 0.5) * 0.00005);
            //gps.lon += (float)((rand.NextDouble() - 0.5) * 0.00005);
            //gps.v += (float)(rand.NextDouble() - 0.5) * 1.0f;

            gps.v   = ((float)Math.Sqrt((velocity.X * velocity.X) + (velocity.Y * velocity.Y)));
            gps.hdg = (float)(((Math.Atan2(velocity.Y, velocity.X) * rad2deg) + 360) % 360);;

            asp.airspeed = gps.v;
#endif

            MainV2.comPort.sendPacket(att);

            MAVLink.mavlink_raw_pressure_t pres = new MAVLink.mavlink_raw_pressure_t();
            double calc = (101325 * Math.Pow(1 - 2.25577 * Math.Pow(10, -5) * gps.alt, 5.25588));
            pres.press_diff1 = (short)(int)(calc); // 0 alt is 0 pa

            MainV2.comPort.sendPacket(pres);

            MainV2.comPort.sendPacket(asp);

            if (framecount % 120 == 0)
            {// 50 / 10 = 5 hz
                MainV2.comPort.sendPacket(gps);
                //Console.WriteLine(DateTime.Now.Millisecond + " GPS" );
            }

            framecount++;
        }
        public void update(ref double[] servos, ArdupilotMega.GCSViews.Simulation.FGNetFDM fdm)
        {
            for (int i = 0; i < servos.Length; i++)
            {
                if (servos[i] <= 0.0)
                {
                    motor_speed[i] = 0;
                }
                else
                {
                    motor_speed[i] = scale_rc(i, (float)servos[i], 0.0f, 1.0f);
                    //servos[i] = motor_speed[i];
                }
            }
            double[] m = motor_speed;

            /*
            roll = 0;
            pitch = 0;
            yaw = 0;
            roll_rate = 0;
            pitch_rate = 0;
            yaw_rate = 0;
            */

            //            Console.WriteLine("\nin m {0:0.000000} {1:0.000000} {2:0.000000} {3:0.000000}", m[0], m[1], m[2], m[3]);
            //            Console.WriteLine("in vel {0:0.000000} {1:0.000000} {2:0.000000}", velocity.X, velocity.Y, velocity.Z);
            //Console.WriteLine("in r {0:0.000000} p {1:0.000000} y {2:0.000000}    - r {3:0.000000} p {4:0.000000} y {5:0.000000}", roll, pitch, yaw, roll_rate, pitch_rate, yaw_rate);

            //            m[0] *= 0.5;

            //# how much time has passed?
            DateTime t = DateTime.Now;
            TimeSpan delta_time = t - last_time; // 0.02
            last_time = t;

            if (delta_time.TotalMilliseconds > 100) // somethings wrong / debug
            {
                delta_time = new TimeSpan(0, 0, 0, 0, 20);
            }

            // rotational acceleration, in degrees/s/s, in body frame
            double roll_accel = 0.0;
            double pitch_accel = 0.0;
            double yaw_accel = 0.0;
            double thrust = 0.0;

            foreach (var i in range((self.motors.Length)))
            {
                roll_accel += -5000.0 * sin(radians(self.motors[i].angle)) * m[i];
                pitch_accel += 5000.0 * cos(radians(self.motors[i].angle)) * m[i];
                if (self.motors[i].clockwise)
                {
                    yaw_accel -= m[i] * 400.0;
                }
                else
                {
                    yaw_accel += m[i] * 400.0;
                }
                thrust += m[i] * self.thrust_scale; // newtons
            }

            // rotational resistance
            roll_accel -= (self.pDeg / self.terminal_rotation_rate) * 5000.0;
            pitch_accel -= (self.qDeg / self.terminal_rotation_rate) * 5000.0;
            yaw_accel -= (self.rDeg / self.terminal_rotation_rate) * 400.0;

            //Console.WriteLine("roll {0} {1} {2}", roll_accel, roll_rate, roll);

            //# update rotational rates in body frame
            self.pDeg += roll_accel * delta_time.TotalSeconds;
            self.qDeg += pitch_accel * delta_time.TotalSeconds;
            self.rDeg += yaw_accel * delta_time.TotalSeconds;

            // Console.WriteLine("roll {0} {1} {2}", roll_accel, roll_rate, roll);

            // calculate rates in earth frame

            var answer = BodyRatesToEarthRates(self.roll, self.pitch, self.yaw,
                                                     self.pDeg, self.qDeg, self.rDeg);
            self.roll_rate = answer.Item1;
            self.pitch_rate = answer.Item2;
            self.yaw_rate = answer.Item3;

            //self.roll_rate = pDeg;
            //self.pitch_rate = qDeg;
            //self.yaw_rate = rDeg;

            //# update rotation
            roll += roll_rate * delta_time.TotalSeconds;
            pitch += pitch_rate * delta_time.TotalSeconds;
            yaw += yaw_rate * delta_time.TotalSeconds;

            //            Console.WriteLine("roll {0} {1} {2}", roll_accel, roll_rate, roll);

            //Console.WriteLine("r {0:0.0} p {1:0.0} y {2:0.0}    - r {3:0.0} p {4:0.0} y {5:0.0}  ms {6:0.000}", roll, pitch, yaw, roll_rate, pitch_rate, yaw_rate, delta_time.TotalSeconds);

            //# air resistance
            Vector3d air_resistance = -velocity * (gravity / terminal_velocity);

            //# normalise rotations
            normalise();

            double accel = thrust / mass;

            //Console.WriteLine("in {0:0.000000} {1:0.000000} {2:0.000000} {3:0.000000}", roll, pitch, yaw, accel);

            Vector3d accel3D = RPY_to_XYZ(roll, pitch, yaw, accel);
            //Console.WriteLine("accel3D " + accel3D.X + " " + accel3D.Y + " " + accel3D.Z);
            accel3D += new Vector3d(0, 0, -gravity);
            accel3D += air_resistance;

            Random rand = new Random();

            //velocity.X += .02 + rand.NextDouble() * .03;
            //velocity.Y += .02 + rand.NextDouble() * .03;

            //# new velocity vector
            velocity += accel3D * delta_time.TotalSeconds;
            this.accel = accel3D;

            //# new position vector
            old_position = new Vector3d(position);
            position += velocity * delta_time.TotalSeconds;

            //            Console.WriteLine(fdm.agl + " "+ fdm.altitude);

            //Console.WriteLine("Z {0} halt {1}  < gl {2} fh {3}" ,position.Z , home_altitude , ground_level , frame_height);

            if (home_latitude == 0 || home_latitude > 90 || home_latitude < -90 || home_longitude == 0)
            {
                this.home_latitude = fdm.latitude * rad2deg;
                this.home_longitude = fdm.longitude * rad2deg;
                this.home_altitude = fdm.altitude * ft2m;
                this.ground_level = this.home_altitude;

                this.altitude = fdm.altitude * ft2m;
                this.latitude = fdm.latitude * rad2deg;
                this.longitude = fdm.longitude * rad2deg;
            }

            //# constrain height to the ground
            if (position.Z + home_altitude < ground_level + frame_height)
            {
                if (old_position.Z + home_altitude > ground_level + frame_height)
                {
                    //                    Console.WriteLine("Hit ground at {0} m/s", (-velocity.Z));
                }
                velocity = new Vector3d(0, 0, 0);
                roll_rate = 0;
                pitch_rate = 0;
                yaw_rate = 0;
                roll = 0;
                pitch = 0;
                position = new Vector3d(position.X, position.Y,
                                               ground_level + frame_height - home_altitude + 0);
                // Console.WriteLine("here " + position.Z);
            }

            //# update lat/lon/altitude
            update_position();

            // send to apm
            #if MAVLINK10
            ArdupilotMega.MAVLink.mavlink_gps_raw_int_t gps = new ArdupilotMega.MAVLink.mavlink_gps_raw_int_t();
            #else
            ArdupilotMega.MAVLink.mavlink_gps_raw_t gps = new ArdupilotMega.MAVLink.mavlink_gps_raw_t();
            #endif

            ArdupilotMega.MAVLink.mavlink_attitude_t att = new ArdupilotMega.MAVLink.mavlink_attitude_t();

            ArdupilotMega.MAVLink.mavlink_vfr_hud_t asp = new ArdupilotMega.MAVLink.mavlink_vfr_hud_t();

            att.roll = (float)roll * deg2rad;
            att.pitch = (float)pitch * deg2rad;
            att.yaw = (float)yaw * deg2rad;
            att.rollspeed = (float)roll_rate * deg2rad;
            att.pitchspeed = (float)pitch_rate * deg2rad;
            att.yawspeed = (float)yaw_rate * deg2rad;

            #if MAVLINK10

            gps.alt = ((int)(altitude * 1000));
            gps.fix_type = 3;
            gps.vel = (ushort)(Math.Sqrt((velocity.X * velocity.X) + (velocity.Y * velocity.Y)) * 100);
            gps.cog = (ushort)((((Math.Atan2(velocity.Y, velocity.X) * rad2deg) + 360) % 360) * 100);
            gps.lat = (int)(latitude* 1.0e7);
            gps.lon = (int)(longitude * 1.0e7);
            gps.time_usec = ((ulong)DateTime.Now.Ticks);

            asp.airspeed = gps.vel;

            #else
            gps.alt = ((float)(altitude));
            gps.fix_type = 3;

            gps.lat = ((float)latitude);
            gps.lon = ((float)longitude);
            gps.usec = ((ulong)DateTime.Now.Ticks);

            //Random rand = new Random();
            //gps.alt += (rand.Next(100) - 50) / 100.0f;
            //gps.lat += (float)((rand.NextDouble() - 0.5) * 0.00005);
            //gps.lon += (float)((rand.NextDouble() - 0.5) * 0.00005);
            //gps.v += (float)(rand.NextDouble() - 0.5) * 1.0f;

            gps.v = ((float)Math.Sqrt((velocity.X * velocity.X) + (velocity.Y * velocity.Y)));
            gps.hdg = (float)(((Math.Atan2(velocity.Y, velocity.X) * rad2deg) + 360) % 360); ;

            asp.airspeed = gps.v;
            #endif

            MainV2.comPort.sendPacket(att);

            MAVLink.mavlink_raw_pressure_t pres = new MAVLink.mavlink_raw_pressure_t();
            double calc = (101325 * Math.Pow(1 - 2.25577 * Math.Pow(10, -5) * gps.alt, 5.25588));
            pres.press_diff1 = (short)(int)(calc); // 0 alt is 0 pa

            MainV2.comPort.sendPacket(pres);

            MainV2.comPort.sendPacket(asp);

            if (framecount % 120 == 0)
            {// 50 / 10 = 5 hz
                MainV2.comPort.sendPacket(gps);
                //Console.WriteLine(DateTime.Now.Millisecond + " GPS" );
            }

            framecount++;
        }