A robot lawn mower is a high-risk DIY project because it combines autonomy with a spinning blade. The safe beginner version copies early commercial mowers: low speed, perimeter wire, bumpers, tilt cutoff and a blade motor that shuts down aggressively. Do not start with GPS-only navigation.
The perimeter wire is the secret that keeps the project tractable. A buried or pegged loop emits a signal the robot can sense, so it knows when to turn around. This avoids needing centimeter GPS or vision that fails in rain and sunlight. Coverage can be random at first; lawns tolerate inefficient paths.
The cutting deck should use small replaceable razor blades on a disk rather than a heavy mower blade. Lower inertia means faster stopping and less energy. Add a physical kill switch before writing any autonomy code.