I have a character with two weapons now. When I export the fbx file and put into unity. Here is a group to group the character , bones, and weapons up. Then I drag the group into hierarchy and put their animations in this model. So that it can run and jump. But I find that it only affect the group model position when the character is running. I just want to see the weapon position. It doesn't change anything in position X,Y,Z. But it is really moveing with the whole character. So how can I get the real weapon position now? I want to do the trail renderer on the weapon.
Take a look at this Unity Answer.
What you need to do is basically loop through your models children until you find the weapon, then once you have that weapon object, you can add the trail renderer to it.