Mechanisms
How The Retracable Pen Works
From the Engineer Guy.
Using the Parker Pen that started it all.
Incredible Engineering Resource
1700 mechanical mechanisms. In 3D. On video so that you can see how they work.
http://makezine.com/2015/04/20/understand-1700-mechanical-linkages-helpful-animations/
The YouTube Channel.
https://www.youtube.com/user/thang010146/videos
This is a huge resource for engineers and makers
A random video.