The hip joints of today's popular bipedal robots have many limitations. More articulation in this area would allow much greater range of motions.

After playing around a bit, I have come up with a design which I intend to use in my RoboDo project. Here's a rough picture...

The "stride" servos (the topmost ones) are connected to their respective legs with either chain or gears, which allows us to reduce the 180 degree servo motion to 120 degrees. This will produce a modest gain in power while limiting the travel in this joint to 75 degrees forward and 45 degrees backwards.

The main benefit however, is that this allows us to have the leg joint supported by a solid shaft and 2 bearings.

The leg rotate servos are also supported by 2 bearings. I just don't like the idea of hanging the whole leg off of a single, cantilevered support point.

At first glance, the "leg lift" servos (the lowest ones pictured) may seem redundant, but these servos will allow RoboDo to kick higher when the legs are rotated to their normal walking position, and allow freedom of motion in this area when the legs are rotated to other positions.

More soon...