I'm addicted to building flying things and have my own port of Arducopter 3.1.5 for Atmega Multiwii boards (https://github.com/alphacharlie/bleedupilot)
What good is any mad scientist without a Tesla Coil???
My home-built eBike using a Bafang 750W motor and a NuVinci n360 rear hub and a 48V LiFePO4 battery.
Built a mini-kossel 3D printer for use in my projects. Video build log of this project starts here - https://www.youtube.com/watch?v=rRxY7Sw2EXE
A Dog Wheelchair for a disabled corgi friend of mine. (Video at https://www.youtube.com/watch?v=krbjR8BKX-Y )