A simple rig with constraints
Sometimes, there are issues that come up when animating that do not require a simple solution. While there may be more elegant or complex ways to solve the problem (which may be necessary in some instances) often, any solution that works is valid. In this case, the need is a basic motion when the object (an R2D2 type robot) has its foot pulled foreword, the leg should seem attached to both foot and body, and the body should stay aligned with the top rotational point on the leg. Check out the video to see how a few constraints can solve the problem.
You can download the sample file for free on Gumroad here: