I am building a RC version of the Lego Land Rover Defender (42119) and it will include a 3 speed sequential Transmission.
It will be operated from the Powered-Up Lego app. using 3 buttons and it includes a dial that shows the selected gear. I am using a Technic Hub (88012) and a Technic Medium Angular Motor (45603). The Remote Control has 3 buttons; up-shift, down-shift and neutral. When the application is started it calibrates the shifting axle to be at the "neutral" gear and sets the angle to 0. Pressing the up-shift button will engage the 1st gear, then if pressed again the 2nd until it reaches the 3rd gear. If you press the up-shift button more times it will not move the shifting mechanism but will make a "clanking" noise. Pressing the down-shift button will sequentially shift to the next lower gear until it gets to neutral where again will make a "clanking" noise trying to go lower. To the right of the 3 buttons there is a dial that indicates the gear is selected.
[Media]