The Devalbo Robot Journal: Battery Blanks - a Lego Mindstorms NXT Power Supply

One of the things I want to do is leave my robot running while I'm not at home. Robot systems typically assume you will use batteries, which is fine if the robot's only on when you're actively engaging it or if you've invested time/energy for a charging station. However, for some of the work I'm doing, I'm willing to tolerate a tethering solution so that I have an "always on" option without having to figure out tethering logistics.

I want to do this "always on" option with a Lego Mindstorms robot - I looked online and could not find a power supply to buy. I did some googling for other solutions, and the only relevant links I could find were this project, which was more involved than I wanted, and this Kickstarter project that didn't go anywhere.

So it was up to me to come up with a solution. The NXT brick uses 6 AA batteries, which means the NXT brick uses 9 volts. So I did a little thinking - all I really need is to get 9 volts between the battery terminals inside the brick. I didn't want to alter the NXT brick in any way, which meant soldering to the brick wasn't an option. I realized that as long as I'm careful, I can get away with something that has the form factor of a battery. (Warning, if you decide to do this, make sure you make your connections properly and don't get the polarity wrong! I can't be held responsible if you plug things in backwards or don't use the right voltages! Do this at your own risk!)

This path led me to wooden dowels, and I did a little research - AA batteries have a roughly 1/2" diameter, so I got a 1/2" dowel and cut it into a couple of battery length pieces. Wood won't carry current, but screws and washers will. With this knowledge, I devised a plan...