AP_Scripting: add motor failure testing applet

libraries/AP_Scripting/applets/forward_flight_motor_shutdown.md

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+# Forward flight motor shutdown script for tailsitters and tiltrotors
+
+This allows to shutdown selected motors to be stopped once in forward flight for efficiency.
+
+Set the motors to shutdown in with the `stop_motors` variable. Enable and disable the functionality with a RC switch with options 300 (Scripting1).
+
+Motors will automatically be shutdown if forward throttle is lower than the value set in `throttle_off_threshold` (50% by default) the motors will then be re-enabled if the throttle goes above the value set in `throttle_on_threshold` (75% by default).
+
+Time for stopped motors to go from throttle value to 0 and 0 back to throttle can be set with `slew_down_time` and `slew_up_time`.

libraries/AP_Scripting/applets/motor_failure_test.lua

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+-- This is a script that stops motors in flight, for use testing motor failure handling
+
+-- add new param MOT_STOP_BITMASK
+local PARAM_TABLE_KEY = 75
+assert(param:add_table(PARAM_TABLE_KEY, "MOT_", 1), "could not add param table")
+assert(param:add_param(PARAM_TABLE_KEY, 1, "STOP_BITMASK", 0), "could not add param")
+
+local stop_motor_bitmask = Parameter()
+assert(stop_motor_bitmask:init("MOT_STOP_BITMASK"), "could not find param")
+
+-- find rc switch with option 300
+local switch = assert(rc:find_channel_for_option(300),"Lua: Could not find switch")
+
+-- read spin min param, we set motors to this PWM to stop them
+local pwm_min
+if quadplane then
+  pwm_min = assert(param:get("Q_M_PWM_MIN"),"Lua: Could not read Q_M_PWM_MIN")
+else
+  pwm_min = assert(param:get("MOT_PWM_MIN"),"Lua: Could not read MOT_PWM_MIN")
+end
+
+local stop_motor_chan
+local last_motor_bitmask
+
+-- find any motors enabled, populate channels numbers to stop
+local function update_stop_motors(new_bitmask)
+  if last_motor_bitmask == new_bitmask then
+    return
+  end
+  stop_motor_chan = {}
+  for i = 1, 12 do
+    if ((1 << (i-1)) & new_bitmask) ~= 0 then
+      -- convert motor number to output function number
+      local output_function
+      if i <= 8 then
+        output_function = i+32
+      else
+        output_function = i+81-8
+      end
+
+      -- get channel number for output function
+      local temp_chan = SRV_Channels:find_channel(output_function)
+      if temp_chan then
+        table.insert(stop_motor_chan, temp_chan)
+      end
+    end
+  end
+  last_motor_bitmask = new_bitmask
+end
+
+function update()
+
+  update_stop_motors(stop_motor_bitmask:get())
+
+  if switch:get_aux_switch_pos() == 2 then
+    for i = 1, #stop_motor_chan do
+      -- override for 15ms, called every 10ms
+      -- using timeout means if the script dies the timeout will expire and all motors will come back
+      -- we cant leave the vehicle in a un-flyable state
+      SRV_Channels:set_output_pwm_chan_timeout(stop_motor_chan[i],pwm_min,15)
+    end
+  end
+
+  return update, 10 -- reschedule at 100hz
+end
+
+return update() -- run immediately before starting to reschedule

libraries/AP_Scripting/applets/motor_failure_test.md

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+# Motor Failure testing Lua script
+
+This script allows testing failure of motors on copter and quadplane (VTOL only). Vehicles with eight or more motors should be able to fly easily with a single failed motor. Hexacopters can also cope with motor failure if they have sufficient thrust.
+
+Motor failure is triggered by a RC switch configured to option 300 (Scripting1). Switch low all motors will run, switch high will stop motors.
+
+Configure which motors stop with the param MOT_STOP_BITMASK, this is added by the script so will only show up once the script is loaded on the SD card. The parameters is a bitmask of motors to stop. A value of 1 will stop motor 1, value of 2 stop motor 2, a value of 3 stops both motors 1 and 2.