Lab 6 Kinematics & Constraints

Make 2 and 3-D models

Work as individuals but refer to lab partners

Read Doug Blanding’s booklet for ideas

Start with 2-D models out of manila folders

Punch works well for making holes for joints

Stick pins for grounded joints

Thumbtacks for free joints

Suggested models – single constraint

One grounded joint – only rotationOne swivel joint – rotation and translation

Dual in-line constraints

Ground joints 1 & 4 and make 2 & 3 a little longWhat happens? Toggle or oil can effect

Dual constraints – not parallel – virtual pivot

Dual constraints - parallel

Instantaneous center of rotation is at infinityBut translational modes constrainedAdd second set of parallel constraints

Cascading constraints

Practical application – Drafting machine – parallel motion in 2-D

Exact 2-D constraints

Design a “tangent bar” constraint for a circular diskThis is often used for the radial constraint of a telescope mirror

Practical examples of 2-D exact constraints

2-D exact constraint table

3-D exact constraint table

Build 3-D constraint systems

Use swab sticks, capplugs and hot glue gun to make modelsCareful with the glue gun – the glue can burn if it is still hot

Make some compound connections

Use manila folder sheet material and glue gun

Investigate stiffening sheets

2-D Trusses

Rigid 3-D structures