AP_Scripting: add copter-circle-speed.lua example

Co-authored-by: Iampete1 <iampete@hotmail.co.uk>

libraries/AP_Scripting/examples/copter-circle-speed.lua

@@ -0,0 +1,36 @@
+-- Maintain a constant ground speed while flying in Circle mode even if the pilot adjusts the radius
+--
+-- CAUTION: This script only works for Copter
+-- this script waits for the vehicle to be armed and in circle mode and then
+-- updates the target rate around the circle (in degrees / sec) to maintain the desired ground speed
+
+local circle_ground_speed = 6 -- the ground speed in circle mode (m/s)
+
+function update() -- this is the loop which periodically runs
+
+  -- must be armed, flying and in circle mode
+  if (not arming:is_armed()) or (not vehicle:get_likely_flying()) or (vehicle:get_mode() ~= 7) then
+    return update, 1000 -- reschedules the loop, 1hz
+  end
+
+  -- get circle radius
+  local radius = vehicle:get_circle_radius()
+  if not radius then
+    gcs:send_text(0, "speed-circle.lua: failed to get circle radius")
+    return update, 1000
+  end
+
+  -- set the rate to give the desired ground speed at the current radius
+  local new_rate = 360 * (circle_ground_speed / (radius*math.pi*2))
+  new_rate = math.max(new_rate, -90)
+  new_rate = math.min(new_rate, 90)
+  if not vehicle:set_circle_rate(new_rate) then
+    gcs:send_text(0, "speed-circle.lua: failed to set rate")
+  else
+    gcs:send_text(0, string.format("speed-circle.lua: radius:%f new_rate=%f", radius, new_rate))
+  end
+
+  return update, 100 -- reschedules the loop, 10hz
+end
+
+return update()