Hey there, I registered an account to ask this, and possibly many more questions to come. This is my first 'true' experiment with electronics, aside from computer building, and a short lab I did last year in college.
I'm trying to build a simple robot, whose only function right now is to move forward. I have two servos (modified for continuous rotation, and such) connected to a plastic sheet with wheels attached to them. The servos were connected to the 5 and 9 pin, and I wrote a program that made them spin in a loop. I was ready to see the robot move portably, so on a breadboard, I added a 6V NiMH battery, and I connected the power wires from the servos. On the Arduino, I had wires going to the 9 and 5 pins, and wires coming from the 5V, and GND to the breadboard, hooked up to the correct polarity.
The thing started to smoke quickly, and feel warm, so I unplugged it quickly. I removed everything from the Arduino, waited a few minutes for it to cool down, and then plugged the USB cable into my computer. The Arduino didn't smoke, but it had a faint 'smoking' smell, so once again, I unplugged it. I felt along the bottom, and the only places where it was warm were the two external power connections (USB and DC ones)
..What did I do wrong? I'm sorry if this question has been answered before, but I'm still pretty new to this, and I honestly don't know how to search for a problem like this. Other people talk about their 5V regulators being the hot parts, but mine is cool. It doesn't help that 'burning' has another meaning when we're talking about these things, haha.
Oh, also, I connected a LED to pin 13 and GND, and it stays lit,even when the board is heating up... I'm not sure if that information is useful, but there you go.