Many popular designs in the current Mix and Match season include:
Number 1: The Revolver: uses a conveyor to place pins inside of a “revolver” that can hold up to four stacks of three. It is difficult to build but is easy to drive.
Number 2: (I call it Uptake) It has a conveyor similar to the revolver, but the storage only uses one stack of 3 in the back claw. It is a bit difficult to build but is easy to drive.
Number 3: Pintex: It uses a 180 degree claw that can flip pins over and place them onto a beam. (A claw in the back is also used to pick up a beam.) It is a simple build but is more difficult to drive.
Number 4: Pinhead: Pinhead uses a large intake consisting of tires that have a good grip on the pin. These tires boost the pin up to the top of a compartment that stacks a stack from the bottom. The Intake is also connected to a 4-bar lift that is used to place the pin back down onto a goal or on the field.
I would also recommend watching this video for more information.
