I have long been a fan of Adafruit. They offer some really amazing kits, complete with specs, schematics, examples and all kinds of wonderful code and instructions for the tinkering. I’ve had many hours of fun building and tweaking projects consisting largely of their components.
I have built robots in the past but they had turned out to be more cumbersome than expected. They were heavy and buggy. A lot of this was due to designs that were overkill (a bit too ambitious). Since that time I’ve wanted to build something a bit more lean, simple and fun to operate.