Fourbar Mechanism Kit

The fourbar mechanism is the simplest pin-jointed linkage that gives a single degree of freedom of controlled motion. It is also one of the most common mechanisms in machinery, and one of the most versatile in terms of the kinds of motion it can produce.

This kit introduces the fourbar pin-jointed mechanism to mechanical engineering students. The link lengths are interchangeable, so the same panel can be reconfigured to demonstrate the double crank, double rocker, and crank-rocker variants.

Specifications

Working panel	40 × 40 cm with 4 supports
Links	2 × 50 mm, 70 mm, 100 mm, 150 mm
Special link	1 triangular link
Joints	2 bearing joints, 2 screws, 2 nuts
Bearings	6 plastic ball bearings (22 mm OD / 6 mm ID)

Learning outcomes

• Identify the main types of fourbar mechanism: double crank, double rocker, and crank rocker.
• Measure the position of different links from an input position.
• Draw the angular position curve of the output (θ3 and θ4) as a function of the input θ2.
• Draw the path of an arbitrary point on the mechanism.
• Discuss, propose, and apply the modifications needed to transform a fourbar mechanism from one type to another (for example double rocker to crank rocker).