If they are using smaller blades, those blades are most certainly spinning much faster than the large blades of a riding or push mower. Thus you're just trading mass for speed and the energy exchange can remain largely the same. You can see this for yourself if you drop items (like a handful of sunflower seeds to simulate rocks) through a spinning ceiling fan or a smaller table fan spinning significantly faster; both can easily throw those seeds that get hit by the blades around a large room. This is how the smaller blades on a lawn mower would even be able to do the same work as the larger blades of a mower.

Also many devices, like table saws, chainsaws, and lawn mowers and considered inherently dangerous to operate. Lawsuits over injury as a result of misuse (like letting children or pets into the yard while mowing) usually have to factor in this inherent danger. There are certain safety measures in place, but I guarantee no mower operator manual suggests letting kids or pets play around a mobile set of spinning metal blades. If you fail to follow the basic instructions in an operators manual while operating a dangerous device, you don't have much ground in a lawsuit.

[–] gamermanh@lemmy.dbzer0.com 3 points 1 month ago

If they are using smaller blades, those blades are most certainly spinning much faster than the large blades of a riding or push mower

No, why would they need to? Grass is insanely easy to cut, so long as you have a decent amount of blades, torque, and can get the cut grass out of the way of the blades then you absolutely don't need speed

See: scythes

[–] Noobnarski@lemmy.world 3 points 1 month ago* (last edited 1 month ago)

The difference with all those other tools is that you are always there when it runs. You are not there when the robot lawnmower is running and some cat jumps your fence, which is why it should not harm the cat.

You are kind of correct that the rpm of the robot mower blades are faster, but the blades are much lighter and most mowers even have swiveling blades that are only held straight by the centrifugal force, so they will just swivel away when they hit something.

The blades are not much more than razor blades that are mounted on a plastic disc with one screw each. You wouldn't want to put your hand into the spinning blade, which is very hard to do anyway, but there is just not enough power to throw rocks with any significant force.

I would be able to put my finger in the way of the blades if they were completely blunt and I would not get hurt very much if at all, doing the same thing on a normal mower would be a very different story.