Specifications

188
Here's some emergency help if you are having problems making the model work: HandPump.2.zip
contains
the three modified files from this lesson.
The next step is to hook the hands up to the handles and get the arms moving in Lesson 3: Kinematics
.
Lesson 3: Kinematics
So far we have added a revolving segment - a hand wheel - to the standing model. In this lesson we shall
deal with the kinematics in the sense that we are hooking the hand up to the handles on the wheel. This will
make the arms move with the wheel as it turns and it is a convenient and simple way of realizing what
would otherwise be a rather complex movement.
Before we begin it is worth noticing that we did a successful kinematic analysis at the end of the preceding
lesson. This shows us that the model is kinematically determinate, so there is a balance between joint
degrees of freedom and constraints in the model. So now that we wish to add constraints by hooking the
hands up to the handles we must remove a similar number of the existing constraints. Otherwise the model
will have redundant and mutually incompatible kinematic constraints and refuse to move or even assemble.
The model's arms are currently driven by:
• three joint angles in the shoulder (the gleno-humeral joint)
• one joint angle in the elbow
• one pronation angle of the forearm
• two joint angles in the wrist
If we attach a hand to a handle by a spherical joint we will be adding three constraints to the model, and we
must correspondingly remove three of the constraints mentioned above. We cannot just remove three
random constraints. For instance, we know that the model is going to have a variation of the elbow angle, so