Ramp It Up
Introductory Presentation
Opening Activity
With a partner, attempt the following:
1. Stand against a wall facing out
2. Have your partner stand in front of you to catch
you if needed
3. Be sure your feet and waist are touching the
wall the entire time
4. Try to touch your toes without falling over
Opening Activity
As you found out, it is impossible to touch your
toes. The reason you can’t is because once you
bent over you’ve moved your center of mass
outside of your support polygon.
Don’t worry, we’ll define both of these for you.
Preview: Center of Mass
The center of mass is the
average position of an object’s
weight. Your center of mass is
located approximately in the
center of your body above
your waist.
Preview: Center of Mass
Another way to think about center of mass is as
the point in an object where:
• The mass above the point =
AND…
the mass below it
• The mass in front of the point =
AND…
the mass behind it
• The mass to the left of the point =
the mass to its right
Preview: Center of Mass
If these weights are all
identical, then the center of
mass would be where the
three lines intersect.
Preview: Support Polygon
Your center of mass could move all around with
no problem, if it weren’t for its support polygon.
A support polygon is the shape formed by
connecting all the points where an object
touches the ground.
Preview: Support Polygon
If you’re standing up, your support
polygon is formed by the place
your feet touch the ground.
Preview: Support Polygon
Suppose you’re on your hands and knees,
like a baby. What shape is your support polygon?
It would be a square, because
each hand and foot touches
the ground. So there are four
points. Connect them, and you
have a square.
Preview
Let’s think back to our wall
exercise. There, your feet were
against the wall and created
your support polygon. Your
center of mass was above your
waist and you were fine.
Preview
However, once you bent over
you moved everything above
your waist, including your
center of mass. You lost your
balance once your center of
mass went outside of your
support polygon.
Preview
It’s important to consider your robot’s
support polygon is, and where its
center of mass may go while running.
If not, you may end up
with something like this…
Good Luck!
Now you have the necessary knowledge to get
started in the Ramp It Up Activity.