How can i detect collision in melee combat?

Hi to all In my game i have two group of ai characters(i.e. red and blue)and red ai could attack to blue's.my npc's have a "charactercontroler" component and their attack animation is melee type such as punching or Spurn attack without any weapon.Since my npc's collider is a capsule like(charactercontroler)and their hand or leg dose not had collider,how can i detect colliding with other npc's? I try adding a separate collider(capsule collider) to their hand and leg,but it did'nt work. any suggestion or help would be appreciated. excuse me for my bad english.