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4-speed Sequential Transmission With Chiron Selectors

Idea for a 4-speed remotely controlled transmission using the new selector pieces from the Bugatti Chiron set. Instructions available.

One of the major new things about the LEGO 42083 Bugatti Chiron set was the brand new selector piece, that allows to shift Lego transmission rings by rotating an axle – a perfect solution for shifting a transmission remotely using a motor. I found, however, that it’s not so easy to design a brand new transmission with these pieces, because the new selectors are designed to control two transmission rings with some spacing between them, not two adjacent rings like in the older design. This makes things much more complicated, and as a result most transmissions designed specifically for the new selectors are large, complex, and not overly effective. For that reason, I’ve decided to adapt my older 4-speed sequential transmission with a stepper shifter design, and make each Chiron selector only control one ring in it. The result is a transmission that is fairly small, simple and effective (few idle gears, no overdrive), but requires two Chiron selectors for 4 speeds, whereas two selectors can control up to 8 speeds, if meshed with two rings instead of just one.

The building instructions for the transmission are available here: http://sariel.pl/downloads/

The transmission uses a total of 10 gear wheels, plus extra 4 for coupling the two selectors together, it offers gear ratios from 5:1 to 1:1, and its input and output axles are aligned, just 1 stud apart, and two-sided, meaning that they can be used in front or in the back of the transmission unit. In other words, the input and output axles go through the entire transmission unit. The stepper mechanism makes sure that every rotation of the shifter motor (which can be any motor, but PF M is recommended for its small size) only shifts the transmission by 1 speed, up or down, depending on the motor’s direction. The transmission can be shifted while driving, endlessly, up or down. Being a sequential transmission, it’s endlessly looped so if you shift up from the 4th speed, you get back to the 1st speed and so on. It also needs to shift through all speeds, so you can go 2-3-4-1-4-3 but you can’t go 2-4.

Finally, not that while the transmission unit is built to withstand plenty of stress, it needs to be braced on the sides. The pins that stick out on the sides should be put into beams or bricks, so that the transmission unit is braced lenghtwise and the two 5×7 frames in it are kept together.


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