Choosing the Right Physics Engine in Gazebo: ODE, Bullet, or DART for Your Robot Simulation

Problem: Picking a Physics Engine for a New Robot Simulation

When you first author a Gazebo world, you’ll be asked to pick a physics engine. The choice affects how joints behave, how collisions are detected, and even the stability of your simulation. If you pick the wrong engine, you may end up with hard‑to‑debug joint errors, unrealistic soft‑body behavior, or performance bottlenecks.

Thesis: Match the Engine to Your Robot’s Morphology and Desired Dynamics

Each engine in Gazebo – ODE, Bullet, and DART – has a niche. ODE is fast for simple rigid bodies, Bullet adds soft‑body and compliant joint support, and DART offers modern constraint solving for complex articulated robots. Understand the trade‑offs before you lock in a choice.

1. Engine Overview

• ODE (Open Dynamics Engine): Default in Gazebo < 9. Good for mobile platforms and basic manipulators. Uses approximate convex decomposition for collision.
• Bullet: Introduced in Gazebo 7. Supports soft‑body, joint compliance, and integrates well with ROS 2 control. Handles mixed hard/soft dynamics.
• DART (Dynamic Animation and Robotics Toolkit): Stabilized in Gazebo 11+. Provides skeleton‑based dynamics, advanced constraint solvers, and a C++ API that matches modern robotics libraries.

2. When to Use ODE

ODE shines when:

• Simulating a differential‑drive car or a small wheeled robot with a few joints.
• You need maximum performance and low CPU usage.
• Your geometry is simple (boxes, cylinders, spheres).
• You don’t require soft‑body or compliant joint behavior.

3. When to Use Bullet

Bullet is the go‑to for:

• Robots with a mix of hard and soft bodies (e.g., a gripper with a compliant pad).
• Articulated manipulators where joint compliance or damping is critical.
• Environments where you want more realistic collision responses (e.g., a robot pushing a stack of boxes).
• Workflows that already use ROS 2 control plugins that depend on Bullet’s joint API.

4. When to Use DART

DART is ideal if:

• You’re researching advanced kinematics or control on a high‑DOF arm.
• You need precise constraint handling (e.g., tight joint limits, backlash modeling).
• You’re comfortable with a newer API and can rebuild plugins against DART.
• Your simulation must run on Gazebo 11+ and you want the latest solver improvements.

5. Practical Example: Switching a World from ODE to Bullet

Suppose you have a world file my_world.sdf that currently uses ODE. You want to enable soft‑body simulation for a deformable object you added.

1. Open the SDF file and locate the <physics> block:

<physics type="ode" name="default_physics">
  <max_step_size>0.001</max_step_size>
  <real_time_factor>1.0</real_time_factor>
</physics>

2. Change the type attribute to bullet:

<physics type="bullet" name="default_physics">
  <max_step_size>0.001</max_step_size>
  <real_time_factor>1.0</real_time_factor>
</physics>

3. Save the file and restart Gazebo.
4. Verify the engine switch by running:

gz world my_world.sdf --verbose | grep "Physics Engine"
# Expected output: "Physics Engine: Bullet"

5. Check that the soft‑body object now deforms as expected. If you see joint errors or crashes, ensure that any plugins compiled against ODE are recompiled for Bullet.

6. Trade‑offs & Limitations

• Performance vs. Accuracy: ODE is fastest but can produce less accurate collision responses for complex shapes. Bullet is slower but more accurate for soft bodies.
• Plugin Compatibility: Many existing Gazebo plugins target ODE. Switching engines may require recompilation or code changes.
• Geometry Support: ODE’s convex decomposition can fail on highly concave meshes, leading to missed collisions or jitter.
• Version Constraints: DART support is only in Gazebo 11+. If you’re on an older release, you must upgrade or stick to ODE/Bullet.

7. Actionable Checklist

1. Identify your robot’s morphology and dynamic needs.
2. Map those needs to the engine table below.
3. Check your Gazebo version with gz version and ensure the chosen engine is available.
4. Update the <physics> tag in your SDF file.
5. Recompile any plugins that depend on the physics engine.
6. Run a quick sanity test: launch the world, observe joint behavior, and verify collision detection.
7. Profile CPU usage to confirm performance meets your target.

Engine	Best For	Key Strengths	Known Issues
ODE	Simple mobile robots	Fast, lightweight	Approximate collision, limited soft‑body
Bullet	Soft‑body & compliant joints	Soft‑body, ROS 2 control integration	Higher CPU, requires plugin recompilation
DART	High‑DOF articulated robots	Advanced constraint solver, modern API	Only in Gazebo 11+, migration effort

Conclusion

Choosing the right physics engine is a design decision that can make or break your simulation workflow. Use ODE for speed on simple robots, Bullet when you need soft‑body or compliant joint dynamics, and DART for research‑grade articulated systems. Always verify the engine in the SDF, recompile plugins, and profile performance before committing to a large project.