CoM polygon constraint#
Statically, it is known that keeping the center of mass of a mobile robot within its support polygon (the convex hull of the contact points) is necessary to prevent the robot from tilting over.
The CoMPolygonConstraint can be used to enforce the (2D) CoM
to stay within a given polygon.
Creating the constraint#
Adding this constraint can be done as follows:
# Support polygon (must be clockwise)
polygon = np.array([
[-0.15, 0.],
[0.02, 0.15],
[0.02, -0.15]
])
# Adding the constraint, with 1.5 cm margin
com_constraint = solver.add_com_polygon_constraint(polygon, 0.015)
com_constraint.configure("com_constraint", "hard")
Here, the polygon is a list of 2D points (on the ground) defining the clockwise support polygon. Clockwise means that the points are ordered in such a way that the interior of the polygon is on the right of the line going from one point to the next.
Updating the constraint#
The constraint can be updated at any time, by setting the polygon
and the margin attributes of the constraint:
# Updating the polygon and margin
com_constraint.polygon = polygon
com_constraint.margin = 0.015
Example#
The CoMPolygonConstraint is used in the following example, where a quadruped
robot is trying to reach targets while not tilting over:
Quadruped reaching targets while not tilting