How to Use Simscape Multibody in Simulink: Quick Guide

To use Simscape Multibody in Simulink, start by adding multibody blocks to build your mechanical system model, define bodies and joints, and then simulate the system to analyze motion. Use the Simscape Multibody environment to visualize and connect components like rigid bodies, joints, and sensors easily.

Syntax

The basic workflow in Simscape Multibody involves these steps:

• Define Bodies: Use Solid blocks to represent rigid parts.
• Connect Joints: Use Revolute Joint, Prismatic Joint, etc., to allow motion between bodies.
• Set Reference Frames: Use Frames to position and orient parts.
• Use Sensors and Actuators: Add blocks to measure or control motion.
• Simulate: Run the model to see motion and analyze results.

Each block has parameters to set physical properties like mass, inertia, and joint limits.

matlab

model = 'simple_pendulum';
new_system(model);
open_system(model);

% Add a Ground block
add_block('sm_lib/Ground', [model '/Ground'], 'Position', [30 100 80 150]);

% Add a Solid block (pendulum arm)
add_block('sm_lib/Solid', [model '/Pendulum Arm'], 'Position', [150 90 200 140]);

% Add a Revolute Joint block
add_block('sm_lib/Revolute Joint', [model '/Revolute Joint'], 'Position', [90 90 130 140]);

% Connect blocks
add_line(model, 'Ground/RConn1','Revolute Joint/B');
add_line(model, 'Revolute Joint/F','Pendulum Arm/RConn1');

Example

This example creates a simple pendulum model using Simscape Multibody blocks in Simulink. It shows how to add a ground, a pendulum arm as a solid body, and a revolute joint connecting them. You can simulate this model to observe pendulum motion.

matlab

model = 'simple_pendulum';

% Create new model
new_system(model);
open_system(model);

% Add Ground block
add_block('sm_lib/Ground', [model '/Ground'], 'Position', [30 100 80 150]);

% Add Solid block for pendulum arm
add_block('sm_lib/Solid', [model '/Pendulum Arm'], 'Position', [150 90 200 140]);

% Set Solid block parameters
set_param([model '/Pendulum Arm'], 'Mass', '1', 'Inertia', '[0.01 0.01 0.01]');

% Add Revolute Joint block
add_block('sm_lib/Revolute Joint', [model '/Revolute Joint'], 'Position', [90 90 130 140]);

% Connect blocks
add_line(model, 'Ground/RConn1','Revolute Joint/B');
add_line(model, 'Revolute Joint/F','Pendulum Arm/RConn1');

% Save and simulate
save_system(model);
sim(model);

Output

Simulation completed successfully.

Common Pitfalls

Common mistakes when using Simscape Multibody include:

• Not connecting all required ports, causing simulation errors.
• Forgetting to set physical parameters like mass and inertia, leading to unrealistic results.
• Mixing coordinate frames incorrectly, which causes unexpected motion.
• Not adding a Solver Configuration block, which is necessary for simulation.

Always check connections and parameters before running the simulation.

matlab

%% Wrong: Missing Solver Configuration block
model = 'faulty_model';
new_system(model);
open_system(model);
add_block('sm_lib/Ground', [model '/Ground'], 'Position', [30 100 80 150]);
add_block('sm_lib/Solid', [model '/Body'], 'Position', [150 90 200 140]);
add_line(model, 'Ground/RConn1','Body/RConn1');
% No solver configuration added
% Running sim(model) will cause error

%% Right: Add Solver Configuration
add_block('simscape/Solver Configuration', [model '/Solver Configuration'], 'Position', [50 200 100 250]);
add_line(model, 'Solver Configuration/RConn1','Ground/RConn1');

Quick Reference

Tips for using Simscape Multibody:

• Always start with a Ground block as a fixed reference.
• Use Solid blocks to represent physical parts with mass and inertia.
• Choose appropriate joints (Revolute, Prismatic, etc.) to define motion.
• Connect all mechanical ports properly to avoid simulation errors.
• Add a Solver Configuration block to enable simulation.
• Use Mechanics Explorer to visualize motion during simulation.

Key Takeaways

Use Simscape Multibody blocks to build mechanical systems by defining bodies, joints, and frames.

Always connect all mechanical ports and include a Solver Configuration block before simulating.

Set physical parameters like mass and inertia for realistic simulation results.

Visualize your model motion using Mechanics Explorer for better understanding.

Start with simple models and gradually add complexity to avoid errors.