Initial angular position of a mechanical system in SimScape

Dears,

I am working on a SimScape model that includes a rotating mechanical system. The model uses an ideal angular velocity source to generate a (fixed) rotation speed, and an ideal rotational motion sensor to measure both the speed and the angular position. Now, when solving the model, it seems that the initial angle of the system (at t = 0) is not equal to zero, but rather some high value (in the order of 1e10). I've tried setting the initial angle in the ideal rotational motion sensor block to 0 but that does not help. Moreover, it seems that the initial angle of the system changes based on the requested speed (I would not expect such a dependency).

I have included a simplified example of the model that includes the components and issues described above. The model is created in Matlab 2020b (the version which I am currently using).

I would like to understand how I can set the initial angle of the mechanical system to zero (at t = 0). Could you help me solve the issue?

Thanks in advance for your help!

Answer 1

[Namnendra]

Hello Ruud,

I understand that you want to set the initial angle of the mechanical system to zero (at t = 0).

It sounds like you're encountering an issue with the initial conditions of your SimScape model, specifically with the initial angle of your rotating mechanical system. This can be a common issue when dealing with ideal sources and sensors in SimScape. Here are some steps to troubleshoot and resolve the issue:

1. Check the Initial Conditions of the Angular Velocity Source:

Ensure that the initial conditions for the angular velocity source are set correctly. Sometimes, the initial conditions of the source can affect the entire system.

2. Set Initial Conditions in the Solver Configuration:

SimScape models use a solver configuration block to set initial conditions. Ensure that the initial conditions are set correctly in the solver configuration block.

3. Use a Rotational Reference Block:

Ensure that you have a rotational reference block connected to your system. This block defines the zero angular position and can help stabilize the initial conditions.

4. Initialize Using a Simulink Signal:

Sometimes, initializing using a Simulink signal can help. You can use an initial condition block connected to a Simulink-PS converter to set the initial angular position.

5. Check for Algebraic Loops:

Algebraic loops can sometimes cause unexpected initial conditions. Ensure that there are no algebraic loops in your model.

Here are some steps on how you can modify your SimScape model to set the initial angle to zero:

1. Add a Rotational Reference Block:

Ensure that your model includes a rotational reference block. Connect this block to the mechanical rotational system to define the zero angular position.

2. Set Initial Conditions in the Solver Configuration Block:

Open the solver configuration block and set the initial conditions for the angular position to zero.

3. Initialize Using a Simulink Signal:

Add an initial condition block and a Simulink-PS converter to your model to initialize the angular position.

Ensure that your model includes similar configurations to set the initial angle to zero. If the issue persists, you might need to check for any other blocks or configurations in your model that could be affecting the initial conditions.

I hope the above information helps you.

Thank you.