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Add Model Dynamics

Dynamic forces are forces that change over time in and depend on system states. Including dynamic forces, or dynamics, in your model improves fidelity but also increases model complexity. In Simscape Driveline, you can add dynamics in the parameterizations of some blocks or you can add blocks to capture the specific required dynamics. 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 the model from the Build a Model and Visualize Results tutorial by entering:


Rotational model with an Ideal Rotational Motion Sensor block and a Scope block that measure the output speed of the Simple Gear block.

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

To represent a dynamic interaction such as backlash in the gearing, you must first add inertia to the system. Add an Inertia block between the Simple Gear block and the Rotational Free End block.

Rotational model with added inertia.

Double-click the Simple Gear block and select Enable backlash under 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.

Backlash causes vibrations in the Simple Gear block speed at port F.

The Simscape solver uses a smaller step size to capture the vibration caused by the gear backlash, which results in a higher computational cost. 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.

Increasing the inertia causes this system to have faster dynamics.

The model is more stiff. The number and magnitude of oscillations during the step response increased due to the change in inertia. This is because it takes more energy to damp the oscillations of the larger inertia.

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