DC motor model in Simscape doesn't give sensible output after adding gearbox and friction blocks

DC motor model within Simscape worked fine before adding a simple gearbox and friction block. With sensible parameters to friction block (breakaway friction torque and velocity, coulomb friction torque and viscous friction coefficient), and simple gearbox (only ratio 280). Output speed from motor is very low (before gearbox) and response to step voltage input shows flat and very low response. Have I made an obvious error in inserting the gearbox and friction blocks ? Have tried many different parameter values but nothing affects the response. Everything worked wekk before these block were added, including parameter estimation tool.

[Joel Van Sickel]

Can your share your model. I don't see anything explicitly wrong with the setup, so I'd need to look at the parameters you are using the response that you are seeing to analyze if something is wrong.

[Mehmet Salih Hamarat]

I think the problem might be due to the breakaway velocity parameter. It defines the separation between static and dynamic regions. Based on your velocity profile, I suggest you to try more sensible value. For example if your velocity profile has a range of -0.1 to 0.1, try 0.001 for breakaway velocity.

Answer 1

[Brahmadev]

Hi William,

From my understanding of the model, you are getting a flat response after adding the “Rotational Friction” and “Gear Box” blocks. Here are some potential reasons for it.

When adding a gearbox and friction block to a DC motor model in Simscape, it's important to ensure that the parameters and configuration are set correctly. Double-check the Gearbox Ratio, Units of torque, velocity, and other parameters and Friction parameters. If the problem persists, it is likely due to the value of the “input voltage (V)” that could be causing the angular velocity to oscillate.

From my understanding of the Model, you might be interested in observing the angular velocity across the “Inertia” block but the “Ideal Rotational Motion Sensor” is connected across the Friction block. A connection as shown below might be more meaningful.

You can refer to the below MathWorks documentation of the "Rotational Friction" block for understanding the parameters.

https://in.mathworks.com/help/simscape/ref/rotationalfriction.html?s_tid=doc_ta

You can also refer to the Example: “Mechanical Rotational System with Stick-Slip Motion” from the below MathWorks documentation for more clarity on the connections.

https://in.mathworks.com/help/simscape/ug/mechanical-rotational-system-with-stick-slip-motion.html

Hope this helps!