NOTE: This is for a non-FRC application.
I have a robot that I would like to power from a Battery (3S LiPo with a Traxxas Female Connector) or a Power Supply (12V with a Traxxas Female Connector). Among the electronics on the robot is a linux board that would not do very well with removing power without a proper shutdown process. While in development the robot would be powered off the power supply, and when testing would run off the battery. So switching between the two would be common. I don't want to run the power supply and battery in parallel as that would not have very good consequences, so I'm looking for some type of power switch that can switch between either the power supply or the battery but acts as a "make before break", so power is never interrupted to the rest of the robot.
Does anyone have any recommendations for a switch like this? The cost ideally would be around $20-$30, the robot sees at most 30A @ 12V and can't be too big, maybe an inch or two. Here are some reference pictures:
https://github.com/dgitz/icarus_rover/wiki