Continuously variable transmission
The belt between the two cones needs to be the same length to stay taught.
As long as the rate that the distance between the 2 cones changes is the same speed and in the opposite direction, it is clear that the belt length does not change.
This shows that it is possible to have an engine that can increase the gear ratio without pausing to switch out one gear for another.
No matter how you change the cones (shape, size, distance apart, etc) the belt will stay taught if the following rules are followed:
1) Cones (triangles here) are congruent
2) Rate of change between blue cones is the same magnitude, but opposite direction of red cones
