This is my last biped creation: the idea started as emprovement

of Alpharex walking mechanism: in fact, since I built the original humanoid,

I disliked the "rubber" grip lever on right foot to make it turn.

(who has built Alpharex, knows well what I mean!)  

Here, each motor controls a leg and robot can turn quickly left or right.

When program is started, legs must be 180 degrees out of phase.

To walk straight, motors move at the same speed and in the same direction;

to turn, motors turn in opposite directions.

This biped can be slightly modified to be built only with NXT set parts:

it is enough to replace 1x2 Technic liftarms (the cams) with two 24z gears.

Motor shaft speed is reduced by 8:24 before being applied to walking  cams, made with Technic 1x2 liftarms.

The mechanism allows each leg to move forward, backward and to shift weight of robot.

  I must admit that the foot design is heavily based on Alpharex one.

As you can notice, I used motor as structural part of the leg,

allowing weight shifting.