I got so many comments and questions about the watt balance illustration that I thought I would make a separate post to cover them all.
How long have you been drafting?/Where did you learn to draw?
I have never been formally taught hand drafting, but I did take a couple of CAD (Computer Aided Drafting) classes in college. Some of my colleagues at work can draw really well, so I've been slowly trying to teach myself. I still have a long way to go, but I really like doing technical drawings by hand. It is definitely a lost art in the age of CAD, and I don't think anyone teaches it anymore.
What is the process you used?
I did the rough layout for the drawing using DraftSight, which is a free 2D CAD package. I am much quicker on the computer than by hand, so I prefer to start there. Then I penciled the drawing to scale using my architectural scale and straight edges. I inked the drawing (shown on the video). Finally I did some cleanup using GIMP for the final print. I made a few mistakes during inking, and I wasn't too proud of my lettering. I ended up replacing the callouts with a "font" of my own letters. Hopefully I'll get good enough at lettering that I don't have to do that next time, but for now I still need some practice!
Why didn't you show the pencil part in the video?
I did the pencil work over the course of a few weeks in my spare time, so it would have been challenging to set up the lights and cameras over and over again. Plus I wasn't sure if I would be proud of the results (i.e. if it would even be worth filming).
Where can I purchase a reasonably-priced print of the drawing and support your channel at the same time?
Funny you should ask. I have prints available in the Practical Engineering Shop.