How many blades does a robot mower need?

1. From 4 to 6 blades: maximising cutting efficiency

Generally speaking, the ideal number depends on the specific cutting system a machine uses. While standard market options typically feature three to six rotating razor-style blades or a single solid mulching disc with two to four blades. STIGA models optimize this layout by utilizing 4 blades on smaller robots and 6 blades on larger models.

Robot mowers operate on a completely different principle than standard push mowers. Because they trim the lawn a little bit every day, this continuous mulching strategy demands a cutting system built for exactness and frequency rather than brute force.

By placing several small, pivoting blades around the cutting disc, the mower ensures uniform coverage, multiplies the cutting action per spin, and eases the mechanical strain on each individual blade.

This 4 to 6 blade setup is crucial for the overall quality of the cut. STIGA blades are designed with a deeply sharpened edge, ensuring a larger active cutting area that cleanly slices through the grass stem rather than just scraping the tips. This clean action avoids the harmful tearing often caused by dull or poorly arranged blades.

A clean cut matters for your lawn, since torn grass leaves jagged wounds that stress the plant and make it highly vulnerable to diseases. A sharp, precise cut, on the other hand, allows the grass to seal and heal rapidly, ultimately fostering a thicker, greener, and healthier lawn over time.

The rotating speed of the motor is a vital component of cutting quality. STIGA robots utilize high-speed blades driven by powerful brushless motors that can rotate at impressive speeds, up to 2850 rpm. To put that into perspective, that is a blistering 47.5 full rotations every single second. This extremely rapid rotation is critical because it ensures that more energy is provided to the blades to grant a sharp cut. This high-speed energy transfer guarantees that the grass is severed cleanly and instantly, which is particularly important during the robot's frequent daily mulching sessions.

Carbon steel is an exceptionally effective material for robot mower blades, as it can be engineered to deliver a precise, long-lasting cut, even though its extreme hardness requires specialized blade geometry. 

The material used for STIGA blades is a high-carbon steel (1.2-1.3) alloyed with chromium, generally used for making cutting tools and springs. Our custom blade weighs 4 grams and has a hardness of 60 HRC. A high-carbon steel, tempered to achieve the hardness mentioned, sacrifices all (or almost all) flexibility for hardness. It's therefore very hard, but very rigid, not flexible. 

One unique and specific point, that speaks for the quality of STIGA robots' blades is the geometry of the double-angle cutting edge, or compound bevel. The blade has a primary bevel with a 7.5° semi-angle, which ensures precision and clean cutting (prevents fraying of the grass), and then, in the last 2 tenths of a millimeter, a secondary bevel with a 17.5° semi-angle. This second, wider bevel strengthens the cutting edge (prevents it from chipping too easily) and ensures longer-lasting sharpness.

A highly appreciated benefit of robotic lawnmowers is how quietly they operate. However, a fast-spinning cutting disc equipped with several steel blades can easily produce loud metallic sounds if the engineering isn't spot-on.

STIGA tackles this issue by utilizing a specialized carbon steel mixture that delivers both durability and built-in resonance-dampening qualities. By perfectly balancing structural strength with vibration absorption, the blades are prevented from vibrating at frequencies that cause the irritating metallic clinking or rattling typically found in lower-quality blades or uneven cutting mechanisms.

Ultimately, this ensures an exceptionally quiet mowing experience where the only thing you hear is the gentle snipping of the grass. STIGA autonomous robot mowers operate at a noise level of just 59 dB(A). To put this into perspective, the robot is as quiet as a standard household refrigerator. Consequently, you can run your STIGA robot mower at any hour without worrying about bothering the neighbors or ruining the tranquility of your garden.

The design of a robotic mower's cutting mechanism is far more than a simple technicality; it is the absolute core of the machine's overall performance. STIGA's strategy is built on four deliberate design choices: employing 4 to 6 blades to guarantee optimal lawn coverage, selecting a high-carbon steel alloy engineered for maximum hardness and edge retention, shaping the blades with extra weight and a deeply sharpened edge for clean slicing, and utilizing a powerful brushless motor capable of reaching 2850 RPM to maintain a rapid, high-energy spin. Ultimately, this combination ensures that each time a STIGA robot trims your garden, it does much more than just reduce the height of the grass—it actively promotes a thicker, more robust, and vibrant lawn over time.