The single most important thing I’ve learned about arcs is:
They are soooo important!
No joke, tracking your arcs and making them look pretty can really elevate the level of your animation. Have you ever wondered why your animation looks clunky? You probably don’t track your arcs. That was my problem for awhile.
So, you may ask, how do you track your arcs? It’s simple. If your tracking the arcs of your character’s wrists you place a dot at each frame on top of the wrist. Then you look to see if you have a smooth arc. Here’s an example where I tracked the arcs from live footage:
If you’re using Maya you can use the Grease Pencil to track your arcs or my preferred method of using the BHGhost script that you can get here. It’s a pretty nifty tool that tracks your arcs quickly.
As a side note, if you are animating for VFX you don’t need to worry about your arcs being as clean. If you are animating for something more cartoony you need to have clean, smooth arcs. I learned that from one of my mentors and wanted to pass it along. ;)