Hi everyone!The problem of the biped walker has exicted every robot maker at least once! But one problem that is not often very well known is the one of the "dynamic" biped walker... Let me explain:
Most of lego biped are "static" walkers : their stability criteria is to keep their center of gravity (COG) inside their footprints. It works pretty good, but if you just look at the way you walk, you'll realise that you actually don' t move your own COG( which is approximately located behind your navel) on top of your feet.
That is because your body is embedded in its own movement, it' s the phenomen of inertia. It is the same kind of forces that pushes you when you suddenly slow down whith your car.
A "dynamic" biped is a walker that masters inertia (like any humanoid robot today). When the robot is moving, the point to keep inside the footprints is not exactly the COG, but a point called ZMP ( Zero Moment Point). If some of you are interested, it is the point on the floor where the sum of the torques of the forces of inertia and of the weight is equal to zero.
You can find more iformation about the ZMP here.
I skip all the boring math stuff I had to perform to make sure to keep BiBob's ZMP inside its footprints, just note that I had to modelise BiBob whith the software SolidWorks (my school owned it) to get the properties of mass, as shown on this picture.I was so able to know what trajctory give to the robot to have a good enough tajectory of the ZMP.
And finally, the robot walks pretty good, here is a video of BiBob walking :
Bobly yours.
