HW: Midterm Project Thinking

My thought process for my project has been less than conclusive. I want to create some kind of robot that interacts with outside objects. My original idea was to create a robot that became happy or annoyed when presented with different items, but I realized that there was no real way I could differentiate between items. My current idea is to have the robot lift things. The robot could hold onto a small cardboard panel with copper tape on it, and then have small plastic items with copper tape on the bottoms to complete a circuit when the object is placed, triggering the robot to lift with the small motors. If it can lift it successfully it reacts positively, and if the object is too heavy and drops off the panel, the robot reacts negatively However, currently I'm unsure of how I can have the objects complete the circuit, and how to trigger a response from the robot if the object falls. Also I am unsure of how much weight the motors are able to hold.