If you’re really interesting in the many details that separate functional PCB designs from professionally designed boards, you can’t do much better in the free department than reading Tom Hausherr’s Blog (Mentor Graphics). There’s some exceptionally good info in there. Find any favorites … please post them up in the comments below for other people to benefit from them!
Make a robot friend with Adafruit’s CRICKIT – A Creative Robotics & Interactive Construction Kit. It’s an add-on to our popular Circuit Playground Express, FEATHER and other platforms to make and program robots with CircuitPython, MakeCode, and Arduino. Start controlling motors, servos, solenoids. You also get signal pins, capacitive touch sensors, a NeoPixel driver and amplified speaker output. It complements & extends your boards so you can still use all the goodies on the microcontroller, now you have a robotics playground as well.