Yard Force Compact 400Ri review: An affordable robot lawn mower with collision detection

Robot lawn mowers take one of two approaches to obstacles: either bump into them and turn around, or “see” them using some kind of sensor and avoid them completely. The Yard Force Compact 400Ri is the latter type and uses ultrasound technology to detect when it’s approaching an obstacle before it hits.

This feature is usually reserved for more expensive lawn mowers, with even mowers that cost twice the price still normally relying on the bump-and-turn method.

Yard Force Compact 400Ri review: What do you get for the money?

For under £500, that’s an impressive inclusion, but otherwise the Yard Force Compact 400Ri has a fairly standard design. It has two large wheels at the back and two coasters at the front and is orange and black, measuring 384 x 440 x 206mm (WDH) and weighing 7.4kg. As well as the mower itself, the box contains its charging station, which has a 9m power cable, 100m of perimeter wire and 120 plastic pegs.

It also comes with three spare blades for its cutting system, which uses three blades attached to a spinning disk on the underside of the mower. This has a cutting width of 16cm and, depending on how short you like your grass, the height of the blades can be adjusted to between 20mm and 55mm.

The mower is recommended for gardens up to 400m² in area with a maximum incline of 30%.

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Yard Force Compact 400Ri review: Is it difficult to set up?

Setting up the Yard Force Compact 400Ri is relatively straightforward. One end of the perimeter cable attaches to one of two input clips on the back of the charging station, then tucks underneath the parking plate and runs around the perimeter of the area you want to cut.

The wire has to be 50cm away from the edge of your lawn on the side that has the docking station attached, but 30cm on all other edges. That’s quite a gap and will leave a strip of about 22cm of uncut grass around the edge of your lawn that you’ll need to decide how to deal with separately.

To get the mower going you can simply set it off with the control panel on the top, by choosing how many hours per day you’d like it to run. The choices are four, six, eight or ten hours. Alternatively, you can, over Wi-Fi, control it via a simple Android or iOS app, setting it off and sending it home remotely.

The app adds a few more features, letting you add time zones in which you want the mower to operate, but that’s about it. It’s very light on features compared to the apps that come with the Bosch Indego S+ 500 and Worx Landroid S300 mowers.

Yard Force Compact 400Ri review: How well does it mow the lawn?

Like most robot mowers around this price, the Yard Force Compact 400Ri moves around the lawn randomly. This effectively means that it sets off in one direction and, when it reaches the boundary wire you’ve laid, it stops, turns and heads off in a new direction. While this negates the need for expensive navigation hardware, keeping the price down, it also runs the risk of missing bits of your lawn.

The standard solution to this problem is to keep the mower going and hope for the best. In our tests it did work, with no patch of lawn left unmowed. However, because the mower keeps going, whether it needs to or not, there’s a risk that it will travel repeatedly over the same areas, which can result in unnecessary wear and tear on your lawn.

It’s also worth noting that the shortest 20mm setting on this mower’s cutter is very short indeed. If your lawn isn’t perfectly flat, you might find that a very low setting hits the dirt in places, which can leave your grass looking patchy.

The strength of the Compact 400Ri is its collision detection system. This worked really well in our tests, avoiding everything from plant pots to passing humans, although it can’t detect low-lying objects such as frisbees or dropped clothes pegs.

The downside is that, by default, the invisible barrier it creates between itself and any object it detects is 30cm. You can extend this to 60cm in the app if you want it to be particularly cautious, but you can’t reduce it any further. As with the edges, this will leave an unmowed area around objects such as your rotary washing line, which other less careful mowers would get closer to. This also applies to the docking station, which the mower can’t get close to unless it’s coming home to charge.

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Yard Force Compact 400Ri review: Should I buy it?

The Yard Force Compact 400Ri is the mower to go for if you seek collision detection but don’t want to spend over £500. Its ability to detect objects is genuinely impressive, making it one of the safest robot mowers for owners of busy, well-used gardens.

However, it still uses a basic random movement pattern in an attempt to cut every blade of grass, which means it needs to be operating for hours and risks going over the same ground repeatedly. If this doesn’t appeal, the Bosch Indego S+ 500 maps an area and mows it in vastly more efficient stripes and, if you don’t mind losing the collision detection, the Worx Landroid S300 does a better job of trimming closer to obstacles, although it will bump into them as it does so.