Are Robot Lawn Mowers Safe To Use?
It would be wrong to say that robot mowers were completely safe.
However, because robot lawn mowers operate unattended, multiple safety features are present making robot mowers reasonably safe. My chihuahua-sized dog has had no problems for years and even this one field mouse is still around. Compared to a manual lawn mower, robot mowers are extremely safe. That doesn’t mean the risk isn’t around however.
Built-In Robot Mower Safety Measures
What better way to illustrate the safety of robot lawn mowers than to compare them to regular lawn mowers.
Regular lawn mowers can be extremely dangerous to use. In one quick move, you could lose a limb or your life entirely, even as an adult. In comparison to that, robot mowers can be considered extremely safe. The reason for that is not just the much smaller size of the robot mower, it’s also to do with several built-in safety features for they operate unattended.
These safety features include, but are not limited to: a different cutting system, collision detection, lift and tilt sensors, easily accessible highly visible emergency stop button, perimeter wire to define the cutting area, low ground clearance, more clearance between chassis and blades, blade exposure preventive plastic shield, less powerful motor, smaller blade(s).
1) The Cutting System Is Different
Conventional lawn mowers use a more powerful motor and also bigger cutting blades generating more air flow. There’s more room down there allowing excess grass (or rocks) to either fly out to the side or into the container and not clog up in the process. However, that clearance leaves the blades more exposed to things not meant to cross paths with the blades, but in dealing with those the mower is plenty powerful.
Now compare that to what robot mowers are rocking. The electric motor running on a battery is weak in comparison, the blades almost as small as razor blades, not needing to generate an air flow but simply just nibbling away at grass blades, dropping them down onto the soil as fertilizer right there and then. The blades themselves tucked deeper under the chassis of the robot mower, leaving them less exposed. In some models the blades are surrounded by an extra layer of protective shell of plastic just before the blades, only allowing grass to slip into the blades’ way.
In a simplified manner, there are 2 types of cutting blades I’ve come come across when dealing with these autonomous creatures. One’s a solid cutting blade, the other is what looks like razor blades attached to a rotating disc. The first is less safe than the latter, but both are considerably safer than a conventional lawn mower still.
2) Sensors – Its Window to the Environment
Robot lawn mowers make decisions based on sensor information. As such, most if not all these sensors are designed with safety in mind. The more a robot “knows” about its environment, the better it will be able to suit its intended purpose.
Touch / Collision / Bump / Contact sensor
More expensive models can detect obstacles and navigate around them using, for example, an ultrasonic sensor. Most robot mowers aren’t that sophisticated and rely on touch sensors a lot more. There are many solutions to measuring impact. For one, when the floating chassis around a robot mower becomes displaced when it bumps into something, the movement of that floating chassis will signal the robot mower that it has encountered an obstacle. Some models might only have a front bumper collision detection sensor instead. Either way, that’s a collision sensor at work. And when a robot mower does bump into something, the robot mower stops on its tracks, turns off its blades, recalculates, turns around and drives off to a different direction and after a short while activates its blades again. These processes vary from model to model.
Every robot lawn mower has one of these. A lift sensor detects whether the mower is being lifted. If it determines it is being lifted, everything, including the blades, become to an emergency stop almost immediately.
Another sensor similar to lift sensor. However, this one, the tilt sensor, makes the robot mower stop when it’s beyond a certain angle, usually at 20 to 30 degrees. So were it to drive up a ramp-like obstacle and leave the blades more exposed, the chances are it will come to a stop. Usually at the very same time it usually physically has bumped into the ramp itself a little making it double-stop in its tracks.
There are way more features and things to robot mowers, so I don’t blame you for thinking like you didn’t quite get the full picture you might have been looking for. For a better overview of things, check out this article on how robot mowers work.
Learning From Past Incidents With Robot Mowers
Most accidents are preventable. We can learn a lot from past documented accidents and tests without having to learn about them ourselves the hard way.
PS! The robot mower can still “try” to drive over or up the obstacle at the perfect angle (little animals, feet, etc) before it senses an actual bump or registers the tilt, and with a very unlucky slice things can still go south if the damage is not treated on time.
You can read here about an accident with a cat named Sputnik in Finland when it got injured by the landowner’s acquired new robot lawn mower some time ago. Of course safety standards are a thing too (for example ANSI/OPEI, at least in Europe). There have also been studies on the safety of robot lawn mowers, such as this one, that conclude the obvious: not safe for pets and children.
So what’s the takeaway? Apart from the very super obvious, here’s a few derivations:
- Be mindful about the little ones
- teach them about the mower if you have to, make them aware of it.
- Set it to mow preferably during daylight
- nocturnal animals are active during night; poor visibility for everybody else.
- Check the lawn before you start the mower
- if a child is laying on the grass, maybe it’s NOT so good of an idea to start up the mower?!
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