A Coach Fit for a King
Besides his designs for the bicycle and paddleboat, Leonardo also created a number of drawings of other vehicles. He was very interested in increasing the efficiency of civilian jobs and, as a result, he designed vehicles for nonmilitary usage.
Cars on Springs
While Leonardo designed several horse-drawn carriages, he also leapt into the future with some sketches for a spring-driven vehicle, which could actually be forebearers of the modern automobile. One of Leonardo's drawings shows self-propelling vehicles that used a wheeled platform and coiled springs that were attached to gears, which had to be “wound” by the user. This design is actually similar to those of early automobiles in which drivers had to manually crank the car.
The winding only took care of half the problem, though, since the driver also had to steer. Do you know anyone coordinated enough to sit, steer, stand, and wind all at the same time? We can breathe a collective sigh of relief that Henry Ford didn't steal Leonardo's design.
Give It a Lift
Leonardo also thought about how to make construction easier. As architectural technology developed, the construction trade had to keep up. Lifting heavy materials to increasing heights was a well-documented problem throughout the medieval period (just think about all those cathedrals!) and even earlier; consider the issues that arose with building the Pyramids of Giza. Cranes had been developed by earlier cultures; the Romans used a type of crane in building their monumental buildings and arches, and medieval cathedral builders designed lifting cranes with varying success.
Leonardo came up with several ideas to improve the situation. He sketched a number of designs for cranes that could be used for quarrying. The crane would lift a stone block out of the ground, and then a mechanism would automatically release once the load was out.
Leonardo also drew three-dimensional designs for cranes that pivoted on a platform, which would have been useful for constructing tall buildings. One design was actually mounted onto a trolley. One of the most interesting aspects of Leonardo's crane design is that, while there don't appear to have been any crane models built during Leonardo's lifetime, later engineers have built them from his specifications and found them to be nearly flawless.
So Little Product
You might wonder why so few of Leonardo's designs were ever built during his lifetime, if so many of them have been built in modern times and found to work. Part of the story is probably Leonardo's secrecy—he just didn't want to share his ideas with anyone. And the other part of the story is probably that Leonardo's designs were just ahead of his time—while we can build them today with modern techniques, many of them would have been impossible to actually build during the Renaissance.