A quick doodle in photoshop, I need the easiest way to turn a normal 3d cylinder mesh and render it in line art form.
Edited: I have no idea why the image is this big so sorry...
Here is one way:
Render your scene
Using a completely transparent material, so that only the background color shows
with an orthographic camera, to remove perspective and make it like a diagram
Using Freestyle to draw the lines.
First, the material. This will be in blender internal, not cycles. Just make a normal material, turn on transparency, and turn the alpha to zero. This will make the object completely invisible. You can set the background color by changing the "Horizon Color" in the World tab in the Settings window.
And finally, to draw the lines, first turn on freestyle: there's a checkbox at the bottom of the Render tab of the Settings window. The default settings will create lines at the creases of your object and around the silhouette. To also draw the occluded lines, like the back bottom half of the cylinder, turn off the "visibility" selection criteria for your freestyle line (render layers tab of the properties window):