Never really built a gearbox before but knew the basics of a 2 and 4 speed boxes so i smashed them together and build this kinda small 8 speed gearbox : r/legotechnic
Ultra Compact 8 Speed Sequential Gearbox - LEGO Technic, Mindstorms, Model Team and Scale Modeling - Eurobricks Forums
LEGO MOC 3-speed gearbox with comfortable manual step switch by Don_Santos | Rebrickable - Build with LEGO