This may be more of a "servo" question than an Arduino question so if I'm in the wrong place let me know.
I have been working on a simple robotic arm as a learning project. I have some standard HiTec servos (HS-311 salvaged from an RC plane I don't fly much any more) controlling the lower joints and two HS-55 servos controlling the hand. My sketch reads the value from a potentiometer on analog 2, maps it, and writes to digital pin 10 using servo.write. Similar to the "knob" example sketch. I'm also using an external power source to run the servos and I have a common ground between the servo power and the Arduino board.The servo power is a 600mA NiCad pack and the voltage from the pack according to my multi-meter is 5.4v. I've checked and double checked the connections.
I was testing the joints two at a time (because I only have two potentiometers at this point) and it works perfect with the standard servos. When I hooked it up to the HS-55 they BOTH actually glowed in the back, smoked, and got hot - within seconds of powering them up. I went back to the standard servos and they worked. What could be going on here...any thoughts or suggestions?
The only thing different is my battery pack. I was running a larger 6v pack (1400mA) but it died so I switched to the smaller pack and the problem seemed to emerge...but it still works with the standard servos so that might be a red herring.