Add Model Dynamics

Dynamic forces are forces that depend on and change with system states. Including dynamic forces, or dynamics, in your model improves fidelity but also increases model complexity. In Simscape Driveline, you can add dynamics such as inertia in the parameterizations of some blocks, or you can add blocks to capture the dynamics separately. Start the model design process by omitting dynamic forces, and gradually add dynamics as you increase the fidelity of your model.

This example shows how to add inertia to a simple mechanical rotational model. Open a simple rotational mechanical system model by entering:

openExample('sdl/SimpleRotationalMechanicalSystemExample')

The model uses an Ideal Angular Velocity Source block to represent a driving component such as a DC motor.

Simulating backlash is an example of model dynamics. Backlash occurs when meshing gears start to turn or change direction. The gaps between the meshing teeth cause fast vibrations when the teeth come into contact.

To add backlash, you must first add inertia to the system. Place an Inertia block between the Simple Gear block and the Rotational Free End block.

The default inertia is 0.01 kg*m^2. Double-click the Simple Gear block and select Enable backlash in the Backlash tab. Selecting this parameter enables related parameters that control the effect of the backlash. To analyze the impact of backlash on the output speed of the Simple Gear block, open the Scope block and run the model.

The backlash response to the system startup is relatively small, and there is minimal vibration because the system has a small inertia. Adding inertia adds to the computational cost because the system becomes more stiff and has higher frequency vibrations.

Blocks that represent hard stops or clutches can introduce fast dynamics and numerical stiffness to your Simscape Driveline model. To experiment with model stiffness, set the Inertia parameter in the Inertia block to 1 kg*m^2 and run the simulation again.

The higher frequency vibrations require a smaller step size from the solver because the system is more stiff. To reduce stiffness in the system, add damping.