I found on the web some drawings from da Vinci’s Atlantic Codex, folio 155. They seem to show a built in spanning lever for some crossbows. However, the only copies I can find of this are at the Getty Images site at: (http://www.gettyimages.com/detail/photo/crossbow-from-atlantic-codex-by-leonardo-da-high-res-stock-photography/103727705 ) and they are so small and faint that it is difficult to make out detail. Scroll down on that page to see the other five drawings.
I have tried Photoshopping them, but that was of little help.
Does anyone know of a source of larger copies of these drawings?