Powering the Robot Arm through a wall socket

I haven't been using the Robotic Arm that much lately due to the hassle of getting and installing new batteries. However, since I'm going to make a presentation about the robotic arm tomorrow, I've modified it to take most of its power through a wall socket DC adapter.

The main power source goes through a JST 2-pin connector (it seems common enough, but finding its name was quite a task just given its appearance). Adding 4 D-type batteries in series gives approximately 6V, however I noticed that there was a small cable linking the middle of the 2 batteries to the board. I measured it using my multimeter and sure enough, it was a 3V supply which I guess powers most of the electronics and logic. The main 6V source probably powers the motors, probably through an H-bridge. But without the 3V supply, it's unlikely that the robotic arm would work at all.

I bought a cheap DC adapter with regulated voltage outputs of 3V - 12V with a maximum current of 600mA, which I guessed would be enough current to power the motors. Since I could only set it to one voltage at a time, I selected 6V since the motors would draw more current and drain the batteries more than the logic circuits. I'm planning to create a small circuit to regulate this voltage down to 3V and provide it as a parallel supply. However, now I'm confident the batteries will now last much longer due to the fact that the motors are now drawing their power from the wall socket.

I'll have to post more details next time as it's currently 10pm and I haven't eaten dinner yet (was too busy hacking the robotic arm). Tutorial soon!