Sort of a historical reconstruction.
Idea is to build a simple wooden crossbow that would have been worth to bother to carry to a 12th century battlefield.
So as minimum recuirement this has to have at least matching ballistics with a Mary Rose type longbow and preferably do better in some aspect.
Bow here pulls 60kg with 25 cm draw, the full power stroke 38 cm, that makes ca, 90kg total draw weight
(200#/15") so energy capacity should be about same as 120-150 pound longbow
Rowan bow 55 x 35 mm middle 130 cm string, 20cm deflex, limbs are barely bend at brace height.
I trust rowan to take 0.14 J/cm^3 , yew bow of equal power could be about 1/3 smaller.
I roughed out the tiller with chain saw, so it needs some cleaning up. Thus temporary junk rope bridling and polypropylene string.Just to test the bow and trigger before proceeding any further.
pin-lock with Lillöhus-style flexible tickler should be appropriate for period.