-- Copter descends very rapidly in a spiral pattern to a preset altitude above home
--
-- CAUTION: This script only works for Copter 4.2 (and higher)
-- this script waits for the vehicle to be changed to Guided mode and then:
-- a) flies a spiral pattern using the velocity and acceleration control
-- b) slows the spiral and stops at the preset altitude
-- c) switches to RTL
-- constants
local copter_guided_mode_num = 4 -- Guided mode is 4 on copter
local copter_rtl_mode_num = 6 -- RTL is 6 on copter
local circle_radius_rate_max_ms = 1 -- radius expands at max of this many m/s
local circle_radius_accel_mss = 1 -- radius expansion speed accelerates at this many m/s/s
local accel_xy = 1 -- horizontal acceleration in m/s^2
local accel_z = 1 -- target vertical acceleration is 1m/s/s
local speed_z_slowdown = 0.1 -- target vertical speed during final slowdown
-- timing and state machine variables
local stage = 0 -- stage of descent
local last_update_ms -- system time of last update
local dt = 0.01 -- update rate of script (0.01 = 100hz)
local interval_ms = 1 -- update interval in ms
local last_print_ms = 0 -- pilot update timer
local auto_last_id = -1 -- unique id used to detect if a new NAV_SCRIPT_TIME command has started
-- control related variables
local circle_center_pos = Vector3f()-- center of circle position as an offset from EKF origin
local circle_radius = 0 -- target circle's current radius (this is slowly expanded to circle_radius_max)
local circle_radius_rate_ms = 0 -- target circle's radius is increasing at this rate in m/s
local circle_angle_rad = 0 -- current target angle on circle (in radians)
local target_alt_D = 0 -- target altitude in m from EKF origin (Note: down is positive)
local speed_xy = 0 -- target horizontal speed (i.e. tangential velocity or horizontal speed around the circle)
local speed_z = 0 -- target descent rate currently
local target_yaw_deg = 0 -- target yaw in degrees (degrees is more convenient based on interface)
-- create and initialise parameters
local PARAM_TABLE_KEY = 75 -- parameter table key must be used by only one script on a particular flight controller
assert(param:add_table(PARAM_TABLE_KEY, "FDST_", 6), 'could not add param table')
assert(param:add_param(PARAM_TABLE_KEY, 1, 'ACTIVATE', 0), 'could not add FDST_ACTIVATE param') -- 0:active in Guided, 1:active in Auto's NAV_SCRIPT_TIME command
assert(param:add_param(PARAM_TABLE_KEY, 2, 'ALT_MIN', 50), 'could not add FDST_ALT_MIN param') -- copter will stop at this altitude above home
assert(param:add_param(PARAM_TABLE_KEY, 3, 'RADIUS', 10), 'could not add FDST_RADIUS parameter') -- target circle's maximum radius
assert(param:add_param(PARAM_TABLE_KEY, 4, 'SPEED_XY', 5), 'could not add FDST_SPEED_XY param') -- max target horizontal speed
assert(param:add_param(PARAM_TABLE_KEY, 5, 'SPEED_DN', 10), 'could not add FDST_SPEED_DN param') -- target descent rate
assert(param:add_param(PARAM_TABLE_KEY, 6, 'YAW_BEHAVE', 0), 'could not add FDST_YAW_BEHAVE param') -- 0:yaw does not change 1:yaw points toward center
-- bind parameters to variables
function bind_param(name)
local p = Parameter()
assert(p:init(name), string.format('could not find %s parameter', name))
return p
end
local activate_type = bind_param("FDST_ACTIVATE") -- activate type 0:Guided, 1:Auto's NAV_SCRIPT_TIME
local alt_above_home_min = bind_param("FDST_ALT_MIN") -- copter will stop at this altitude above home
local circle_radius_max = bind_param("FDST_RADIUS") -- target circle's maximum radius
local speed_xy_max = bind_param("FDST_SPEED_XY") -- max target horizontal speed
local speed_z_max = bind_param("FDST_SPEED_DN") -- target descent rate
local yaw_behave = bind_param("FDST_YAW_BEHAVE") -- 0:yaw is static, 1:yaw points towards center of circle
-- the main update function
function update()
-- update dt
local now_ms = millis()
if (last_update_ms) then
dt = (now_ms - last_update_ms):tofloat() / 1000.0
end
if (dt > 1) then
dt = 0
end
last_update_ms = now_ms
-- determine if progress update should be sent to user
local update_user = false
if (now_ms - last_print_ms > 5000) then
last_print_ms = now_ms
update_user = true
end
-- reset stage until activated in Guided or Auto mode
if (activate_type:get() == 0) then
-- activate_type 0: reset stage when disarmed or not in Guided mode
if not arming:is_armed() or (vehicle:get_mode() ~= copter_guided_mode_num) then
stage = 0
if (update_user) then
gcs:send_text(0, "Fast Descent: waiting for Guided")
end
return update, interval_ms
end
else
-- activate_type 1: reset stage when disarmed or not in Auto executing NAV_SCRIPT_TIME command
auto_last_id, cmd, arg1, arg2 = vehicle:nav_script_time()
if not arming:is_armed() or not auto_last_id then
stage = 0
if (update_user) then
gcs:send_text(0, "Fast Descent: waiting for NAV_SCRIPT_TIME")
end
return update, interval_ms
end
end
if (stage == 0) then -- Stage0: initialise
local home = ahrs:get_home()
local curr_loc = ahrs:get_location()
if home and curr_loc then
circle_center_pos = ahrs:get_relative_position_NED_origin()
circle_radius_rate_ms = 0 -- reset circle radius expandion rate to zero
circle_radius = 0 -- reset circle radius to zero
if yaw_behave:get() == 0 then
-- yaw does not move so reset starting angle to current heading
circle_angle_rad = ahrs:get_yaw()
else
-- yaw points towards center so start 180deg behind vehicle
circle_angle_rad = ahrs:get_yaw() + math.pi
if (circle_angle_rad >= (math.pi * 2)) then
circle_angle_rad = circle_angle_rad - (math.pi * 2)
end
end
target_yaw_deg = math.deg(ahrs:get_yaw()) -- target heading will be kept at original heading
target_alt_D = circle_center_pos:z() -- initialise target alt using current position (Note: down is positive)
speed_xy = 0
speed_z = 0
stage = stage + 1 -- advance to next stage
gcs:send_text(0, "Fast Descent: starting")
end
elseif (stage == 1) then -- Stage1: descend
-- get current position
local rel_pos_home_NED = ahrs:get_relative_position_NED_home()
-- increase circle radius
circle_radius_rate_ms = math.min(circle_radius_rate_ms + (circle_radius_accel_mss * dt), circle_radius_rate_max_ms) -- accelerate radius expansion
circle_radius = math.min(circle_radius + (circle_radius_rate_ms * dt), circle_radius_max:get()) -- increase radius
-- calculate horizontal and vertical speed
if (circle_radius < circle_radius_max:get()) then
speed_xy = math.max(speed_xy - (accel_xy * dt), 0) -- decelerate horizontal speed to zero
speed_z = math.max(speed_z - (accel_z * dt), 0) -- decelerate vertical speed to zero
else
-- determine if below slowdown point
local slowdown = false
local stopping_distance_z = 0.5 * speed_z_max:get() * speed_z_max:get() / accel_z
if (rel_pos_home_NED) then
if (-rel_pos_home_NED:z() <= alt_above_home_min:get() + stopping_distance_z) then
slowdown = true
end
end
if (slowdown) then
-- slow down vertical and then horizontal speed
speed_z = math.max(speed_z - (accel_z * dt), math.min(speed_z_slowdown, speed_z_max:get())) -- decelerate to 0.1m/s vertically
if speed_z <= speed_z_slowdown then
speed_xy = math.max(speed_xy - (accel_xy * dt), 0)
end
else
-- normal speed
speed_xy = math.min(speed_xy + (accel_xy * dt), speed_xy_max:get()) -- accelerate horizontal speed to max
speed_z = math.min(speed_z + (accel_z * dt), speed_z_max:get()) -- accelerate to max descent rate
end
end
-- calculate angular velocity
local ang_vel_rads = 0
if (circle_radius >= circle_radius_max:get()) then
ang_vel_rads = speed_xy / circle_radius;
end
-- increment angular position
circle_angle_rad = circle_angle_rad + (ang_vel_rads * dt)
if (circle_angle_rad >= (math.pi * 2)) then
circle_angle_rad = circle_angle_rad - (math.pi * 2)
end
-- calculate target position
local cos_ang = math.cos(circle_angle_rad)
local sin_ang = math.sin(circle_angle_rad)
local target_pos = Vector3f()
target_pos:x(circle_center_pos:x() + (circle_radius * cos_ang))
target_pos:y(circle_center_pos:y() + (circle_radius * sin_ang))
target_alt_D = target_alt_D + (speed_z * dt)
target_pos:z(target_alt_D)
-- calculate target velocity
target_vel = Vector3f()
target_vel:x(speed_xy * -sin_ang)
target_vel:y(speed_xy * cos_ang)
target_vel:z(speed_z)
-- calculate target acceleration
local centrip_accel = 0
if (circle_radius > 0) then
centrip_accel = speed_xy * speed_xy / circle_radius
end
target_accel = Vector3f()
target_accel:x(centrip_accel * -cos_ang)
target_accel:y(centrip_accel * -sin_ang)
-- calculate target yaw
if yaw_behave:get() == 1 then
target_yaw_deg = math.deg(circle_angle_rad + math.pi)
if target_yaw_deg > 360 then
target_yaw_deg = target_yaw_deg - 360
end
end
-- send targets to vehicle with yaw target
vehicle:set_target_posvelaccel_NED(target_pos, target_vel, target_accel, true, target_yaw_deg, false, 0, false)
-- advance to stage 2 when below target altitude
if (rel_pos_home_NED) then
if (-rel_pos_home_NED:z() <= alt_above_home_min:get()) then
stage = stage + 1
end
if (update_user) then
gcs:send_text(0, string.format("Fast Descent: alt:%d target:%d", math.floor(-rel_pos_home_NED:z()), math.floor(alt_above_home_min:get())))
end
else
gcs:send_text(0, "Fast Descent: lost position estimate, aborting")
stage = stage + 1
end
elseif (stage == 2) then -- Stage2: done!
stage = stage + 1
gcs:send_text(0, "Fast Descent: done!")
if (activate_type:get() == 0) then
-- if activated from Guided change to RTL mode
vehicle:set_mode(copter_rtl_mode_num)
else
-- if activated from Auto NAV_SCRIPT_TIME then mark command as done
vehicle:nav_script_time_done(auto_last_id)
end
end
return update, interval_ms
end
return update()