here's the pendulum in action- note the ARC it creates...
2 frames or the extremes
define the tweens upping the frame count to 4
introduce the timing for the weighting of the orb by adding 4 additional ease in and out frames as it goes into the extremes.
These illustrate the basic principles of pendulums, you can extrapolate this concept and now apply it to limbs.
Extremes
Define the Crossover (I'm using a technique here called 'breaking joints' where (in this case) the knee is subtly overextended - this priniciple is used to great effect in a lot of cartoon animation usually a great deal more pronounced - it's a way of adding 'snap' and hidden movement in a short amount of time)
This illustrates the tweening process the purple dotted lines show the leg positions before and after (a crude form of 'onion skinning') - this allows you to pick a point (between the two) to place your next plotted position for you knees, ankles/heel, hip, and foot position - once you've decided those you can then fillin the lines. This is where understanding the pendulum, arcs, and weights come into play.
then you start applying form and mass starting with the calf muscles and bottom
then fill in the lines...
You can do the smae with arms too... just remember to work in opposites, (arm back, leg forward)
Admittedly, this process is very technical in application - and to be honest as you get better you don't need to do all these steps, you will just DO... as it's all in your head... but in order to run you have to learn to walk (pun intended) - regardless of the style of what your end piece looks like these prinicples still apply... and there by no means fixed - all of them can be bent and manipulated to suit your own needs - in fact I'd openly encourage you to find your own method. This works for me in some cases... not all - but like I said the understanding is there regardless.
Finally I thought I'd throw this in to illustrate strectch and squash...
Squash on impact - Stretch on release
The same sequence with added frames (tweens) adds weight with the ease in and out at the top of the sequence
The slightly modified sequence with secondary motion and slightly different timing... incorporating secondary motion (on the tail) and additional stretch, and aniticipation (again on the tail [it delays for 1 frame before pinginig up])
Enjoy...
