Have you noticed that many advanced FIRST Lego League (FLL) robots spend very little time in the robot game "Base" to switch-out attachments? They tend to use a quick-connect system whereby a "shell" can go on top of a motorized platform in a few seconds. This Lego Mindstorms EV3 robot uses the "Dog Gear" idea shown in Builderdude35's YouTube video https://www.youtube.com/watch?v=NZbt3tnySyI . Two EV3 Medium Motors have Power Take Off (PTO) pegs onto which an upper "shell" can interface to drive attachments. In my "Lego EV3 Robot Designs" Flickr album, this render of the yellow layer is the "shell": https:[email protected]/17706676898/in/dateposted-public/ . One EV3 Medium Motor is driving FuzzyCow's DualGrabber attachment ( rebrickable.com/mocs/DavidLuders/dualgrabber-clawgripper ), and the other one is driving the yellow hook. This "Fllying Turtle" design illustrates what is possible with a "Shell" design; there are many ways of routing the motor power to attachments that you design. The LDD .lxf file for the Fllying Turtle + yellow shell is at www.bricksafe.com/files/dluders/Fllying%20Turtle%20EV3%20... ; design your own shell!