Whether you have kids, pets, or just want a helping hand around the house, robot vacuums are useful tools for keeping your home clean. If you pay extra for a model with a self-emptying bin, you don’t even have to touch it for days, if not weeks. But there are hidden costs associated with robot vacuums that first-time buyers might not be familiar with. Not only do you need to empty the bins every so often, you also need to buy replacement parts–especially if, like most owners, you use your robot vacuum every day. If you don’t replace its worn-out parts on a regular basis, your robot vacuum may …