Four Bar Linkage Simulator

What Is a Four Bar Linkage?

A four bar linkage is one of the most basic and widely used mechanisms in mechanical engineering. It consists of four rigid links connected by four rotating joints, forming a closed loop.

The four links are:

1. Ground Link (Link 1) – Fixed base of the mechanism
2. Input Crank (Link 2) – Rotates to drive the system
3. Coupler Link (Link 3) – Transfers motion between links
4. Output Rocker (Link 4) – Produces the final motion

This mechanism converts rotary motion into rotary or oscillating motion, which is why it is found in engines, pumps, presses, and robotic systems.

Why Use a Four Bar Linkage Simulator?

Understanding four bar mechanisms using formulas alone can be difficult. A simulator makes learning easier and faster by providing:

• Real-time motion visualization
• Instant kinematic calculations
• Easy testing of different link combinations
• Clear identification of mechanism type
• Better intuition of transmission angles and motion quality

This simulator bridges the gap between theory and practical understanding.

Overview of the Four Bar Linkage Simulator

The Four Bar Linkage Simulator you provided is an interactive, browser-based kinematic tool with visual animation and analytical outputs.

It includes:

• Adjustable link lengths
• Crank speed control
• Simulation speed control
• Canvas-based mechanism animation
• Automatic kinematic analysis
• Grashof condition detection
• Transmission angle monitoring

All results update instantly as inputs change, making it ideal for experimentation.

Input Parameters Explained

1. Link Length Inputs

The simulator allows you to enter four link lengths within practical ranges:

• Link 1 – Ground Link: Defines the fixed distance between base joints
• Link 2 – Input Crank: Drives the mechanism
• Link 3 – Coupler Link: Connects crank and rocker
• Link 4 – Output Rocker: Produces output motion

Changing these values helps you study different mechanism behaviors.

2. Crank Speed (RPM)

This input controls how fast the input crank rotates.

• Measured in revolutions per minute (RPM)
• Affects time-based motion and animation speed
• Used to calculate the time period of rotation

Higher RPM results in faster motion and shorter cycle time.

3. Simulation Speed Control

Simulation speed does not affect calculations. It only controls visual playback speed.

Options include:

• Slow
• Normal
• Fast
• Very Fast

This is useful for studying motion carefully or quickly previewing behavior.

Visual Mechanism Animation

The simulator uses a canvas-based drawing system to display the mechanism.

Key Visual Features

• Ground link shown as a fixed reference
• Color-coded links for clarity
• Clearly marked joints (A0, A, B, C)
• Crank rotation path visualization
• Transmission angle arc display

This visual feedback makes motion paths easy to understand, even for beginners.

Kinematic Analysis Results

The simulator provides live kinematic data in a dedicated results panel.

1. Output Angle

• Shows the angular position of the output rocker
• Updates continuously during simulation
• Helps study output motion characteristics

2. Transmission Angle

The transmission angle is one of the most important quality indicators of a mechanism.

• Calculated as the angle between the coupler and rocker
• Ideal range: 40° to 140°
• Color-coded for easy interpretation:
  • Green: Good transmission
  • Orange: Acceptable
  • Red: Poor force transmission

A poor transmission angle indicates inefficient force transfer.

3. Crank Position

Displays the current angular position of the input crank in degrees. This helps correlate motion position with output behavior.

4. Time Period

Calculated from crank speed using:

• Time Period = 60 / RPM

The simulator also shows elapsed time within one rotation, helping users connect angular motion with time.

Grashof Condition and Mechanism Type

What Is the Grashof Condition?

The Grashof condition determines whether at least one link can rotate fully.

Rule:

Shortest + Longest ≤ Remaining two links

If satisfied, the mechanism allows continuous rotation.

Mechanism Type Identification

Based on link lengths, the simulator automatically identifies the mechanism type:

• Double Crank (Drag Link)
• Crank-Rocker
• Double Rocker
• Non-Grashof (Triple Rocker)

This is extremely useful for design validation and education.

Simulation Controls Explained

The simulator includes four easy-to-use control buttons:

Start Simulation

• Begins continuous animation
• Uses real-time frame updates

Pause

• Stops motion at the current position

Reset

• Returns crank angle to 0°
• Clears motion history

Step Forward

• Advances motion by a fixed angle
• Perfect for frame-by-frame analysis

These controls make the simulator flexible for both learning and analysis.

Educational and Practical Applications

This Four Bar Linkage Simulator is useful in many areas:

• Mechanical engineering education
• Kinematics and mechanism design courses
• Machine design validation
• Concept testing before CAD modeling
• Research and experimentation
• Online learning platforms

It is especially valuable for students who struggle with abstract kinematic equations.

Limitations and Disclaimer

The simulator performs theoretical kinematic analysis only.

It does not consider:

• Material properties
• Joint friction
• Manufacturing tolerances
• Dynamic forces
• Wear and deformation

Real-world mechanisms may behave differently, so this tool should be used for conceptual and preliminary analysis.