Simple Continuously Variable Transmission
A simple CVT.
Having recently designed a number of efficient remotely controlled sequential transmissions, I wanted to try out a very simple idea for a CVT – a continuously variable transmission. Such a type of transmission doesn’t have fixed speeds and ratios but instead shifts steplessly between the minimum and maximum ratio. My mechanism was a very simple representation of real life’s CVT design that uses two cones facing in opposite directions and connected by an elastic belt. One cone is located on the input shaft and the other on the output shaft, and by moving the belt along the cones’ length we effectively change the section of the cone that is driving and being driven by the belt – and different cone sections have different diameters. Thus by driving a thick cone section by a thin cone section we can gear down, and by driving a thin cone section by a thick cone section we can gear up.
My very simple mechanism used cones extending from 1 stud wide to 3 studs wide, effectively producing minimum and maximum gear ratios of 1:3 and 3:1. Shifting was done using a very simple sliding guide which forced a rubber band connecting the two cones to move along their length. The mechanism demonstrated basic principles of the real CVT transmissions, but also suffered from the same problems that they do – namely, from being ill-suited for high-torque applications. High torque inevitably causes the rubber band connecting the cones to start slipping.
There are no instructions for this variant of the transmission as it’s dead simple and can be easily built from the video.
Video:
