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

Statically Deterministic Introduction Statically Deterministic Force Moment Two force member Degree of Freedom Kinematic constraint

Suggested models – single constraint One grounded joint – only rotation One swivel joint – rotation and translation

Dual in-line constraints Ground joints 1 & 4 and make 2 & 3 a little long What happens? Toggle or oil can effect

Dual constraints – not parallel – virtual pivot

Dual constraints - parallel Instantaneous center of rotation is at infinity But translational modes constrained Add 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 disk This 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 models Careful 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

Tangent Arm

Tangent Arm

Example of Kinematic Constraint

Example of Virtual Pivot

Example of Vee

Example of “Canoe Ball” Large contact surface radius to reduce Hertzian contact stress

Example of mechanical 3D constraint

Example of 3D Constraint

Example of 3D Constraint