self-braking trolley
Terrible idea. I would expect that the brakes would probably slam on at least 20 times during an average supermarket trawl, leaving your arms feeling like you've just danced with a cyberman.
Invent one that can fish itself out of canals and rivers, or just take itself back to the store after being left half a mile away and I might be impressed.
Biting the hand that feeds IT
