It doesn't have a trigger like the other ones because i found out that you can't use the full power of the crossbow then.
It uses the wheels to spread the power across the rubber bands to make it shoot further.
I recently joined and therefore this is my first Instructable and i've tried to make it as detailed as possible.(I'm trying to make a new trigger very soon)
Finally after like 2 years I made a proper trigger xD. It is buildable from the pictures in this topic: