are robot mowers safe my kids

Are Robot Lawn Mowers Safe?

For most people, one of the main concerns about robot lawn mowers is safety. How can automatic robots with spinning blades be safe? The statistics speak volumes in this case.

In 2017, there were zero emergency room visits involving robot lawn mowers in the USA. This compares to more than 80 000 visits involving conventional lawn mowers. Obviously, there are many fewer robotic lawn mowers in operation, compared to conventional lawn mowers. Even still, this is an astonishing statistic.

Having researched this further, I have struggled to find any evidence of serious injury involving a domestic robotic lawn mower. This would certainly back up my personal experience that they are dramatically more safe compared to conventional mowers.

Conventional Mowers Are The Most Dangerous Piece Of Garden Equipment

Today, if you cut your own lawn, rather than paying a gardener to cut your grass, you will mow your lawn somewhere in the region of 30 times per year. It is important to remember that each time you use a lawn mower, you are operating a highly dangerous and powerful piece of machinery. Most lawn mowers use flammable fuel, get extremely hot during operation and use a blade to cut your grass that rotates at more than 3000 rpm that produces three times the kinetic energy of a bullet.

Serious accidents most commonly occur when body parts come into contact with the spinning blades of the mower. Severe limb damage or amputation is all too common. Another common injury occurs when debris or stones are expelled from the cutting blades and hit the operator. Other serious injuries can occur from body contact with the hot surfaces of the mower or ignition of the flammable fuel.

Despite considerable technological advances, conventional lawn mowers still cause 6500 accidents in the UK each year, and over 80 000 emergency room attendances in the USA. Last year there were 95 reported fatalities in the USA due to lawn mower accidents. Looking at the UK statistics, lawn mower accidents are consistently the number one cause of accidents in the garden. The statistical likelihood of being involved in a lawn mower accident if you are a male is 1 in 2,626 and if you are a female 1 in 7,248.

Robot Lawn Mowers Are Remarkably Safe

Robot lawn mowers on the other hand, use completely different cutting systems and technology which reduces the risk of injury massively. They have collision, tilt and lift sensors which cause the mower to stop the blades in a fraction of a second if it is interrupted. The blades also use much less energy than conventional mowers, so that even if a person was to come into contact with a moving blade, the resulting injuries would be much less significant.

Overall, there is no comparison between the two types of machine. Robot lawn mowers are extremely safe and this fact alone is likely to drive market growth of robot mowers in the coming years.

Robot Lawn Mowers Must Be Safe To Be Accepted By The Public

Robot lawn mowers have been in development for well over 30 years, with the first domestic models appearing in the mid 1990s. The developers who hoped to commercialise the technology of robot lawn mowers knew there was considerable public apprehension regarding automated machines with sharp spinning blades. I certainly wouldn’t want to own one unless I knew for sure that the safety aspects were well developed.

Safety Features Of Robot Lawn Mowers Explained

Collision Sensors

Robot mowers move very slowly along the ground, so the impact of a collision is very low. There would be no possibility of injury from a robot mower colliding with a person due to the low speed of impact.

There are four main technologies that robot mowers use for collision detection. 

1. Floating Shell

Many robot mowers use a floating shell surrounding the mower chassis that becomes displaced if an obstacle is encountered, and a Hall Effect sensor that detects shell movement.

2. Accelerometers

Alternatively, some robotic mowers use a soft front bumper along with one or more accelerometers mounted to the mower’s outer shell. Accelerometers detect obstacles when there is an impact, and spikes in accelerometer readings have been used to measure contact.

3. Changes In Wheel Speed

Some robotic mowers detect sudden drops in wheel speed or changes in the control effort required to maintain wheel speed as indications of a bump.

4. Sonar And Lidar

More models now incorporate sonar or lidar detection for ranging into their robot lawn mower models. This enables the mower to detect obstacles as they approach and slow down and stop, prior to coming into contact with the obstacle, or to navigate away from the obstacle. Models such as the Honda Miimo uses this technology to both improve collision detection and to increase the efficiency and reduce the time it takes to mow your lawn.

Overall, robot mowers have been developed with fairly advanced collision detection systems, which enable them to avoid or stop immediately on contact with an obstacle. This prevents any damage to the obstacle or to the robot mower. 

Lift Sensor

Every robot mower on the market is fitted with lift sensors. If the mower’s wheels are lifted off the ground, either by someone lifting the mower intentionally or due to the mower becoming stuck and tilting, resulting in one of the wheels losing contact with the ground, the emergency stop is activated, which stops the blades from spinning in a fraction of a second. This is an important safety feature particularly for curious pets or young children, who may try to move, lift or tilt the mower. Immediate stop of the blades will result in avoidance of injury in these circumstances.

Tilt Sensor

The tilt sensor complements the lift sensor in preventing access to the cutting blades during operation. If the mower is tilted beyond a set angle, the emergency stop is activated and the blades stop immediately. This is useful in situations where the mowers wheels remain in contact with the ground or another object, but there is a risk of the cutting blades being exposed. The lift and tilt sensors in combination make it virtually impossible to access the cutting blades of a robot lawn mower while it is in operation.

Cutting Technology

The cutting technology of robot lawn mowers is significantly different from conventional mowers. Robot mowers typically use one of two cutting techniques to do the job.

Models from Husqvarna and Bosch among others use a spinning disc with small blades attached to it. These blades are similar in size to razor blades and are mounted to the spinning disc with screws which allow them to rotate freely on the mounting. This is apparently a very efficient way of cutting the grass and uses very little power.

The blades are very sharp, allowing them to slice through the grass with ease, but due to the small size, have very little individual power. If the blades encounter a more substantial object, rather than cutting it, they are forced backwards on their mounting and spin round, avoiding damage to the object.

razor cutting disc my robot mower

Robot lawn mowers from companies like robomow on the other hand, use larger, rigid spinning blades. These are solitary in the smaller models and are in pairs in the larger models. These mowers typically have a wider cutting diameter, but the blades require more power to function. This type of cutting system is usually more noisy in operation. Typically, there is a 10 decibel difference in noise output between models that use freely mounted razor blades and those that use rigid spinning blades.

robomow robot mower showing blades

The blades of all robot lawn mowers are tucked well underneath the body of the mower. They usually have minimal ground clearance, ensuring that there is no risk of inadvertent exposure to the blades. As mentioned above, the lift and tilt sensors ensure that if the mower is intentionally or accidentally lifted, the cutting blades will stop virtually instantly. Without exception, the power of the cutting blades of robotic lawn mowers is considerably less than that of conventional mowers and this makes them much safer, even without the the other safety features.

Prevention Of Expulsion Of Stones

The motors of the cutting systems for robot lawn mowers are surprisingly weak. They are normally designed with sufficient power to cut blades of grass, but not to damage more substantial objects. If a robot mower comes into contact with a stone, it is unlikely to have sufficient power to move it far. Due to the enclosed shell around the blades and low ground clearance, it is highly unlikely to expel a stone from under the machine. This largely eliminates the risk of being hit by a foreign object from a robot lawn mower.

Perimeter Wire

Almost all robot lawnmowers on the market today work within the confines of a perimeter wire which is laid out by the owner prior to operating the robot lawn mower. The robot mower uses the wire to know where the edge of the lawn is and prevents it from escaping from the confines of the grass. Therefore, you need not worry about the mower bumping into objects that are on your patio or driveway.

Ability To Handle Significant Gradients

Robot lawn mowers are designed with a low centre of gravity. This ensures that when they are mowing the lawn on a slope, that the risk of them or toppling over and exposing cutting blades remains very small. Some consumer models can manage slopes of up to 25 degrees, or 46%. Although the cutting system of a robotic lawn mower would stop immediately if it did tip on a particularly steep slope, it is definitely preferable that the cutting blades remain underneath the mower, tucked out of the way.

Child Safety

Although robot lawn mowers have many safety features built-in, I would still strongly recommend that you do not leave small children unsupervised in the presence of a working robot lawn mower. If a small child did try to tip or reach underneath a robot lawn mower, the cutting blades would immediately stop and the risk of injury would be very small.

However a very curious child may tip the machine to look underneath it and potentially cut themselves on the stationary blades. Most robot lawn mowers have blades that are designed to be quite sharp, which differs from a lot of conventional lawn mowers. Conventional rotary lawn mowers are designed to knock the top off the blades of grass, so the blades are usually fairly blunt.

Personally, I have two small children aged 4 and 2. I sometimes allow the robot lawn mower to continue operation while I am in the garden playing with my children. I only do this when the children are supervised very closely. If they are spending a longer amount of time in the garden or are going to be unsupervised at all, I simply open the hatch of my robot lawn mower, press the home button and it will return to its docking station to charge until it is reactivated.

are robot mowers safe my kids
My kids love the mower, but supervision is recommended. Harry is demonstrating the location of the emergency stop button.

Pet Safety

Pets can often be even more curious than small children. For cats, I don’t think there is much chance of an injury, as a cat would be unlikely to show sufficient interest in a robot lawn mower. For dogs, in my experience, they typically show a little bit of curiosity at first, but I have never seen a dog try to topple or interfere with a robot lawn mower.

To be honest, it would depend on the individual dog and the preference of the owner.  You will have to decide if your dog would be safe in the garden with a robot mower. The manufacturers of robot lawn mowers have been aware of the issue of pets ever since they started designing them. Therefore, a lot of the safety features that have been developed have been done with pets in mind as well.

In Summary

Safety has been at the forefront in the development of robot lawn mowers for many years. They would not be accepted by home owners unless the safety standards were very high. As discussed above, there is no comparison between the safety of robot lawn mowers and conventional lawn mowers.

I think safety alone is quite a compelling reason to consider switching to a robot lawn mower. There are lots of other things to consider as well that are important in the decision making process. If you would like to read more please follow the link for a comparison between conventional lawn mowers and robot lawn mowers.