I've been trying to get my head around the biomechanics of throwing for a while now. recently I've shared some of the ideas at a few dojo and it seems helpful.
It centres (no pun intended) on looking at the base of support, centre of mass and the optimum angle to apply(the toppling vector). I've put together 2 videos, the first is 10mins of your life you may never get back where i've annotated some film with commentary on a simple example, there are stick figures and some vectors, the second is some outages of free play with toppling.
Pardon my own poor posture in them , as the focus is on looking at uke. It may be helpful or not for some recent aikiweb discussions (but is sufficiently off topic i think to put separately)
Some short text and the video plugins are on
hope you like