sensor range X = something;
velocity Y = something;
weight limit = something;

if 'actor(from own team)' is 'within sensor range X' and is 'within weight limit' then
   'open doors';
      if 'something present in inventory' then
         'direction of travel(velocity Y)' = 'opposite of last direction of travel(velocity Y)'; //this way you won't be needing to add extra code, it will travel in the opposite direction of the last travel (if it went up, it will go down and so on) - only problem is, how will it know where to travel if used for the first time?
         'release cargo';
      end
else 'close doors';
end