Specifications

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The pedal seems to be located in the middle of the pelvis, which is really a symptom of the warning that the
model contains too few kinematic constraints. We have not made any specifications yet of how everything in
the model is connected. This will be the topic of Lesson 7: Making Ends Meet
.
Lesson 7: Making Ends Meet
So far we have accomplished to define an environment model with a simple pedal and a body model
containing a pelvis and the right leg. What the application is still missing is specifications of how the
different elements are connected and how the model moves. With kinematics it is usually a good idea to
begin with an inventory of degrees of freedom (DOFs) in the model.
The pedal is simple: It is hinged to the global reference frame and therefore just has just one movement
capability, namely a rotation about the hinge. The body model is more complicated. It is disconnected from
everything and is therefore floating around in space. Furthermore it has a number of internal degrees of
freedom that must be controlled: Three rotations in the hip, one rotation in the knee, and two rotations in
the ankle. With the six DOFs of the entire body model in space and the single DOF of the pedal, this adds up
to 13 DOFs. In other words, we need 13 constraints before the model is kinematically determinate.
This is what we plan to do:
1. The pelvis will be fixed completely at a point corresponding to the contact to a seat. This will do
away with 6 DOFs leaving us with 7 more to specify.