[PAR_WIG1350]

I know this has already been said, but you CANNOT use more than 2 fisher price motors this year.

That being said, AM-0912 and banebots' RS-550 have the same dimensions and mounting geometries and similar power ratings. You can have up to 2 of the Andy mark motors and 4 Banebots motors. Since you haven't used any Banebots motors yet, you can use 4 550s or some other combination of allowed banebots motors. The RS-775-18 motors are nice, but they are heavier than 550 sized motors and have a greater shaft diameter and different mounting features.