The idea was to use the front gondola to get above an enemy wall and shoot into the areas behind..the second gondola was for another archer /crossbowman to provide covering fire.
It was a real device..honest!!! . The only actual link I´ve found with an explantion is in German or French...HERE
|Wnding gear from florists wire.|
|The hinges for the front barrel and the roller for the rope on the "mast" were made using the inner from a biro (proving usefull ) Slightly heat one end and then pressed against a flat surface, it flattens out. For the roller, both ends.|