Robot mowers frighten me. It's one thing to have a vacuum cleaner blindly stumble around - there's only so much damage it can do. But whirling blades up the let

Robot mowers frighten me. It's one thing to have a vacuum cleaner blindly stumble around - there's only so much damage it can do. But whirling blades up the lethality stakes a lot. The navigational and object-avoidance prowess of Roombas do not convince me that arming them with samurai swords is wise.