AP_Scripting: copter-wall-climber accel limiting

reduces climb rate slowly so it can stop before next interval
also fixup formatting of altitude output to user

libraries/AP_Scripting/examples/copter-wall-climber.lua

@@ -58,6 +58,11 @@ local roll_speed = 0                -- target horizontal roll speed in m/s
 local pitch_speed = 0               -- target horizontal pitch speed in m/s
 local wall_dist_target = 5          -- target distance to wall
 
+-- get the maximum speed in order to decelerate to zero within the given distance
+function get_speed_max(distance, accel_max)
+  return math.sqrt(2.0 * math.max(0, distance) * accel_max)
+end
+
 -- the main update function that uses the takeoff and velocity controllers to fly a rough square pattern
 function update()
 
@@ -152,8 +157,9 @@ function update()
       climb_total = climb_total + climb_chg
 
       -- determine if we should pause
-      if (math.abs(climb_interval_total) >= climb_stop_interval) then
-        gcs:send_text(0, "WallClimb: pausing at " .. tostring(climb_total) .. "m")
+      local dist_to_interval = climb_stop_interval - math.abs(climb_interval_total)
+      if (dist_to_interval <= 0) then
+        gcs:send_text(0, "WallClimb: pausing at " .. string.format("%3.1f", climb_total) .. "m")
         climb_pause_counter = climb_pause_counter_max
         climb_interval_total = 0
 
@@ -169,6 +175,12 @@ function update()
       -- default target climb rate to lane climb rate
       local climb_rate_target = lane_climb_rate
 
+      -- limit target speed so vehicle can stop before next interval
+	  -- speed limit is always at least 0.1m/s so copter doesn't get stuck near interval
+      local speed_max = math.max(get_speed_max(dist_to_interval, climb_accel_max), 0.1)
+      climb_rate_target = math.max(climb_rate_target, -speed_max)
+      climb_rate_target = math.min(climb_rate_target, speed_max)
+
       -- if paused set target climb rate to zero
       if (climb_pause_counter > 0) then
         climb_pause_counter = climb_pause_counter - 1