So they invented the lawnmower. At first, they used “reel” type lawnmowers, which drove a helical set of blades around a horizontal axis parallel to the ground. As the mower pushed, the motion of the wheel made the blades turn. The blades shear against a platen or second blade. These make beautiful lawns, and are still used on golf courses. However, they jam horribly if you try to mow over a stick as big a pencil. Also, they are hard to push, which is an advantage to people who want exercise, which means it is a disadvantage to most Americans.
So they added gasoline powered motors, which manage to pollute about us much as an entire cars while producing fractional horsepower, because they don’t have the sophisticated pollution controls on cars.
But they still had to bend down to pick up sticks so they wouldn’t jam the reel. And, being Americans, they don’t like bending over. So they invented the rotary motor, which spins the blades parallel to the ground around an axis perpendicular to the ground. Rotary motors are so powerful you can mow right over sticks and it just turns them into shorter sticks, leaving the Americans time to go to yoga classes, since they avoided all that bending over.
But very slowly it dawned on Americans that using gasoline to do something like this and then using gasoline to drive to the gym to make up for their lack of exercise was perhaps a situation which could be made more efficient. That’s where this project comes in.
When I was a boy, I mowed a lot of lawns to make money. We had a Yazoo mower, which was vastly superior to other mowers because it gigantic back wheels, almost bicycle wheels. This made it a pleasure to push.
I propose that we develop a human-powered rotary mower that provides exercise and is also able to chop up whatever you want.
By building a chassis with great big back wheels, we can extract power from the pushing to drive a generator. We will have onboard a super capacitor that can store a few seconds worth of power; possibly we will need a battery.
We will drive the blade as an independent action controlled by a a computer and the operator. Either the computer or the operator can tell the blades to go maximum speed when they sense it is time to do some chopping. But when you are just pushing the thing across the driveway to the grass, the blades stop and consume no power, making it easier to push.
Since it may be quite strenuous to provide enough power, we can simply make the cutting size of the blade smaller than a regular mower. This will mean the mower will have to make more walks back and forth across the lawn, but it will not be too hard to push the mower at any one point in time.
We may be able to build a detection system that can sense when we are in high grass and when it is time to start chopping. Similarly, we can detect when we have little chunks of wood flying around and keep up the power until they are all chopped up to a small size.
Like all project of Public Invention, we seek no intellectual property right on this idea — anyone may do freely what they want with it, though this text is released under a Creative Commons Share-alike Attribution license. If you are interested in working on this project, please contact me at <firstname.lastname@example.org>. You may wish to peruse the 30 project ideas at github: https://github.com/PubInv/PubInv/tree/master/ideas.
And by the way, this story is fictitious. You can read about the true history of the lawnmower at Wikipedia.