I don's seem to be able to get any battery power from Create 2. I spliced the original cable it came with, and tried to use the power from red/purple(+) and yellow/orange(-) to power a Raspberry Pi2, with no luck. While the serial-to-USB cable still works, and I am able to command the robot via Python, there seems to be no power coming on the red/purple cables. I tried with a multimeter with no luck, even as I moved the device from passive/safe/full modes. There is no power even when Create 2 is charging/docked.
First off, there's no guarantee the wire colors in the iRobot cable match the colors in the cable made by Tensility. Step one is to get an ohm meter and see if the colors match the pins you expect. If they do, I wonder if you accidentally blew the resettable fuse? See the discussion at the end of the section entitled External Serial Port Mini-DIN Pinout on page 3. Depending on what you've plugged in, you may have pulled more than 200mA. Wait a bit for the fuse to cool, and then with nothing connected to the robot, (carefully) jam a multimeter between pins 6 and 1 on the connector and see if you get battery voltage. If you do, plug your cable in, with nothing attached to the cable but the voltmeter, and see if you get battery voltage where you'd expect it. If that checks out, put an ammeter between the battery power wires and your Pi, preferably in peak detect mode.
Good luck; I hope you have a multimeter.
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