Continuously Variable Transmission is a transmission type that has infinite speed ratio between two ratio limits (maximum ratio and minimum).
The system is based in two cones conected by other element (usually a belt), and moving this element along the cone you can change the transmission ratio in infinite positions.
It doesn't need clutch to change the ratio, but it have a problem, it cann't have reverse, you need add a transmission reserver.
Obviously the maximum allowed torque is limited by the cone connector.
This transmission is very used in scooters and low fuel consumption cars, as the Toyota Prius, because it can keep the engine in the optimal rpm range.
Based in the original desing I had developed a Lego version. In this model de minimum ratio is 1:0.5 and de maximum ratio 1:2
Note: I had use a big linear actuator but the system only need 4-studs displaciment and you can use a mini-LA (I dont have one...)
It uses two opposing cones, with 4-stud maximum diameter and 2-studs minimum.
You can get other limited ratios using other cones size.
The cone connect element is a 30.4x14 tyre
With this tyre the maximum allowed torque is 4 Ncm, this is a M motor torque, or a XL motor with 1:3 external ratio torque
A little video:
You can see more pictures here:
And download step by step instructions here:
I hope you like it!!!