An olive harvester has a nonrotatable outer cap, a rotatable inner cap which is driven by compressed air supplied to the outer cap and which generates a swirl through the olive tree below the inner cap which dislodges the olives so that they can be collected in a skirt which is fixed to the outer cap and surrounds the tree. Upon activation of the group bonus event, a first one of the players playing at one of the gaming devices can challenge one or more other players to participate in the group bonus event. A linkage structure having two degrees of freedom is used for supporting the tension roller, so that the tension roller can automatically move to a position where it does not interfere with either pulley at any transmission ratio. The liquid flows in the housing and sprays from the housing to impact the coverture, so as to make the coverture and the light-emitting device rotate coaxially.