Solenoid engines are nothing new, though they still seem to be a fairly common project among the curious. Using a hard drive makes such a project much more simple and straight forward, that is if you want to keep it that way.
This solenoid engine uses a software control loop (code below) running on a 16MHz Adafruit Trinket to adjust its speed. The program specifically alternates between a modest 180RPM to a smashing 3000RPM every five or ten seconds! Watch the video below!
I pulled a couple 4Ah 3S LiPos from my tricopter’s stash and soldered together a little series adapter to give me an effective 4Ah 6S LiPo pack. The effective range has been cut in half to around 5miles compared to the original 13lb 10Ah SLA pack, but that’s still plenty enough to get someone around a college campus.