You assemble mechanisms (called kinematic-chains, or linkages) with the Parts and Joints - the basic kinematic elements.
Kinematics and Kinematic-Chains
A series of rigid-bodies and joints such that all move in a predictable way given the motion of a minimum of one rigid-body. One rigid-body in a kinematic-chain is the Reference Frame - called the Base-Part in MechDesigner.
A rigid-body is not a real body. It is an ideal-body.
|•||does not stretch|
|•||does not bend|
|•||does not twist|
|•||does not vibrate|
|•||does not expand with heat|
|•||has an exact and specified length|
A Joint allows the relative motion between Rigid-Bodies. It is an ideal-joint.
|•||does not have backlash|
|•||does not resist the motion with friction or other deleterious force.|
|•||does not have a dimension - other than the location of an axis in an ideal-body.|
Machines versus Mechanisms
Machines are those kinematic-chains that do useful work, that transmit forces to transmit power from an input to an output
Mechanisms are those kinematic-chains that transmit motion, or information.
In MechDesigner, there is no distinction. However, there is often a semantic debate as to when a mechanism becomes a machine, and vice versa. The distinction is usually made as the design intent
|•||Machines transmit force. But they also transmit motion from part to part.|
|•||Mechanisms transmit motion. But they also transmit force from part to part.|
Reference Frame: a Frame of reference to identify the relative motion of moving Parts.
Binary Links, Ternary Links, Quaternary Links... Parts with two, three, four and more Points.
We do not 'add' Binary, Ternary and Quaternary Parts. We edit a Part to add any number of Points.
For completeness, Parts with two, three and four Points are shown below.
Joints constrain Parts to move relative to each other in a predefined way. Different types of joint give different relative motion.
A Joint is also known as a 'Kinematic-Pair'. There are three types of Kinematic-Pairs; each gives a different relative motion.
These use Points, Lines and Planes to constrain contact between two Parts with Points, Lines and Planes.
There are six Lower Kinematic Pairs. We have three in MechDesigner.
The other three are: Screw, Cylindrical and Plane on Plane. We do not have these in MechDesigner.
Constrains contact between two Parts with Curves or Surfaces - also called a 'Half-Joint'.
Constrains Points to be in contact with a sketch. It can be used to model belts, chains, and other such devices.
There are two elements for which we specify a motion.
Motion-Parts: You specify the motion of a Part with motion-values at the input to a Motion-Dimension FB.
Motion-Points: You specify the motion of a Point with motion-values at the input to a Motion-Path FB.
The parameter that the Motion-Dimension FB specifies is:
- or -
The parameter the Motion-Path FB specifies is: