For this animation the primary points are the apex of the first arch, the point of impact, and the apex of the next arch, for a full cycle. (Tip: turn on Onion-Skinning so that you can see previous and future frames in outline while you work.) I started by copying my first frame to the very end of my cycle; I chose 13 frames, as an odd number makes it easier to divide at key points with the same number of frames to either side--and this lets me set it at one frame over a second. Once I copied that frame I moved it to the point that the ball would bounce to on its next cycle.
At my midpoint, Frame 7, I drew another circle--flattened from impact, resting to the ground at a point halfway between the two arc apexes. This is my midpoint, and the point where the ball strikes the ground.
