Robot lawn mowers for hills and slopes: how to choose

Slope percent is rise divided by horizontal run, multiplied by 100. Degrees measure the angle. A 45 percent grade is about 24 degrees, not 45 degrees. Compare like with like, and use a reliable level or measurement method rather than estimating by sight.

Measure the steepest part the mower must actually traverse, including short ramps, ditch edges, and transitions. A published maximum may assume dry, firm grass and a straight climb rather than wet turf, side-hill travel, or a turn at the limit.

Driven wheels, tire design, weight distribution, articulation, ground clearance, cutting-deck movement, braking, and control software all affect hill behavior. Four-wheel drive can add capability, but it does not make every steep or slippery area safe.

Look for official guidance on maximum slope at the boundary as well as inside the work area. The allowed grade near a perimeter can be lower because stopping or turning room is limited.

Water, retaining walls, roads, steps, and open drop-offs deserve a physical risk assessment. Virtual mapping and obstacle sensing are useful features, not substitutes for the manufacturer's required setbacks or barriers where a navigation error could cause damage or injury.

Plan drainage and avoid mowing when the surface is too wet. Repeated wheel slip can damage turf even when the mower eventually completes the route.

A mower rated exactly at your measured maximum leaves little room for measurement error, wet conditions, side slopes, or surface change. Shortlist models above the requirement, then compare credible owner reports from similarly shaped properties.