What distinguishes a robot from other mechanisms such as a drone or ROV (remotely operated vehicle) ?
What distinguishes a robot from other mechanisms such as a drone or ROV (remotely operated vehicle) ?
To my knowledge robots are named after a Czech word for forced labour. Therefore my definition would be "A machine which carry out work autonomous." (very much like peteroakes definition). Workshopshed: the word "autonomous" rules out your lawn mower 
Drones are unmaned air vehicles traditionally used as target for aiming exercises. They always are remote operated. Nowadays the carry sensors and weapons, too. Use was to my knowledge only military until recently. I personally would not call my qadrocpter a Drone, because of the military implication. A drone is a flying military ROV.
I'm not sure that there's any distinct difference between robots and machinery. As crjeder says, the word "robot" comes from a Czech play, and was invented as a futuristic word for slave.
That said, there is a difference between robots and androids, which are machines that are designed to mimic the shape and appearance of a man. So C-3PO could be considered an android, but R2-D2 couldn't 
When Obi Wan said "These aren't the droids you're looking for," he was half telling the truth!
Also, it's worth knowing (for pub quiz purposes) that android is a masculine term; the female equivalent is a gynoid.
It's also worth noting that this doesn't help you in the slightest, Workshopshed.
Respect the first comments, a robot that do things completely self-referential like moving but totally autonomously without doing nothing else it is not a robot and can be classified in the range of the useless machines 
So if a robot should do something, we have a couple of different approaches to find the answer.
The first is bare mechanical, so anything that can do a series of coordinate actions maybe considered a robot, including some complex yet efficient engines from the previous centutires. By this point of view for example a self-playing piano is a robot that we program with a punched belt then he can repeat what a human can do.
The second approach is that should do something of intelligent and interactive. I mean from the bare concept of answering to a question up to making very complex action sequences.
As the game theory teach us, we should never be distracted by the complexity of the situation, but the moving algorithm. By this point of view it is less "robot" a machine able to do thousand of actions with a super sophisticate program than a simple engine (i.e. a keyboard and a monitor) able to make complex inferences.
The final point in this though is that none of these can be considered robot in terms of "human like things". Independently by the complexity these are knowledge systems and not thinking systems. Cognitive psychologists can enjoy a lot but these are always lifeless dolls. So in a commonly accepted vision the large meaning of the term robot can be covered by any knowledge system able to manage correctly the links of its internal cognitive base (I don't use the term database because it is minimising the concept). Well all these are robots.
So we can define as robot in a generic definition as a mimic system with a - more or less - complex cognitive engine able to interact with the real world depending on some input conditions. No matter is are sensors, a keyboard or a banana. The point is that all these systems out of their context are simply (again) lifeless dolls.
IMO we use the term robot to generically distinguish fully controlled machines (like an excavator) by autonomous ones (in specific and restricted conditions). What I consider as robot it does no matter, my opinion is that this is one of those terms that should be reviewed and their meaning rewritten periodically to update the word to the actual context.
How do you think that the term robot will match with an experiencing system instead of a knowledge based ?
Enrico