The first project I did was a turtle, with a Lego frame, Raspberry Pi plus 74HC595 serial parallel latch, ULN2801A darlington ampplifiers powering two stepper motors, with a Wifi connection to another RPi application where you can type in commands. It was all powered by a 7.4v Lithium Ion battery via a LDO Switching regulator.
This was done very much step by step, using much of the same circuitry from 25 years ago when I did one at school driven by a BBC Micro, starting first with driving LEDs, then progressing to steppers and then finally seating it in a Lego Techic body.
The commands are sent over a TCP connection from the control machine to the turtle. The turtle was powered by a LiPo battery. If you want more details, click on the TurtlePi category on the right.
I ended up buying lots of little bits of Lego from ebay to get the best combination of gears etc to ensure the large torque needed by the wheels didn’t break the gears or their axles. But one piece didn’t exist: a flat yellow flat dome to drag on the floor under the batteries. At some point, I got hold of a clear yellow one which was ‘good enough’ for the moment but my OCD – every programmer must have OCD to some extent – wouldn’t let it go until I had the correct one in the matching opaque yellow as the rest of the Turtle. One turned up on ebay the other day – I’d kept the watch running – and I couldn’t believe it!
So now I’m a very happy person, and can concentrate 100% on Phoebe!
P.S. I had intended to show a video here, but as I powered up the Turtle, the circuitry heated up, and I think I’ve just blown the 3 stacked ULN2801 darlington drivers – hopefully the 74HC595 survived . Definitely the end of the project for the mo’ though! Oops