How do I connect 6+ controllers at once to the RPI 3b+?

[Landspyker]

G'day, was just wondering how I connect more than 4 controllers via usb to the Raspberry pi 3b+? I wanna have 2 sets of joysticks/buttons, 2 snes controllers and 2 gun controllers.

Is there a way I can plug them all in at once via one of those usb things that allows multiple usb inputs with 1 output or would I just have to plug in the controller i wanna use as I play?

I'm interested in adding a trackball and a flight joystick too.

[Landspyker]

Also thought, would it maybe be possible to add the two traditional arcade controllers to the same usb encoder?

[mahuti]

You can use a USB hub of course. The problem has to do with making one of each set of controllers attached to player 1, and the other work for player 2. By default linux will see each USB port as 1 player.  In your case for instance, player 1 & 2 might have joysticks and buttons and player 3 and 4 would have the SNES controllers, and I'm guessing the gun controllers would be ignored in most emulators since they don't support more than 4 players. MAME is easy enough to configure to use both joysticks as well as the gamepads, but other emulators aren't configurable in the same way.

Anyway, that said, if your goal is to use joysticks and buttons for MAME and SNES controllers for other systems like NES, SNES, Genesis, etc, you could use this:
https://github.com/meleu/RetroPie-joystick-selection

It allows you to set a default controller for the whole system, and override that selection on a per-emulator basis.