Ok, so firstly, I'm not suggesting you go out and buy a Kensington Expert, Slimblade or Perixx Periboard just to get a 55mm trackball to use with this system. That wouldn't make sense as you could buy an X-Arcade or Ultimarc (or many other) arcade trackball setups for that. The idea is that you own one of these trackballs already or maybe that you can get hold of just the 55mm ball part for a cheap price. With the aforementioned ball, six 5mm ball bearings, some rubber bands and a spare optical mouse (plus a 3D printer, obviously) you can put together a small footprint, control panel-mounted trackball to get shooting those Centipedes or Goldening those Tees (?!). Do make sure to test whatever 55mm ball you are going to utilise with your spare optical mouse first tho'. Not all Optical rodents are made the same and I have come across red lasered Microsoft versions that do not like certain spherical surfaces. There is an issue that using an upturned mouse presents tho'; it will reverse one of your axis depending on which way around you mount it. With MAME this isn't a problem as you can just reverse the axis in the games settings menu but if you want to use this trackball for general use then you will find this software useful: Sakasa Mouse (reverses X or Y mouse axis in windows): http://hp.vector.co.jp/authors/VA026826/ Good luck and may your heavy balls spin freely. 4415H means: 4 top layers, 4 bottom layers, 15% infill and H is Hex infill. 4420L means: 4 top layers, 4 bottom layers, 20% infill and L is Line infill. Please consider supporting me on Patreon: https://www.patreon.com/3DFreeman Here's a non-affiliate ebay link to the 5mm ball bearings I use: https://www.ebay.com.au/itm/292968111398?var=591758252496 Thanks for checking out my designs. Print Settings Printer: Aquila X2 Rafts: No Supports: No Filament brand: Voxelab Filament material: PLA