# simulating worn brake pads effect on wheel's rpm

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Gal Shraiter on 1 Aug 2020
Commented: Gal Shraiter on 7 Aug 2020
Hi all,
I'm getting into simulink for academic use, and I'm trying to understand how to show the condition of brake pads on the wheel's rpm on a time series. The diagram should be simple, and values shouldn't be exact, it's a first attempt for me. This is what I have so far, but I'm failing to understand how get the wheel's rpm. On top of that, I'm thinking about making the kinetic friction a variable, and to control it separately. Is that possible? any suggestion on how to move forward? Thanks!

Steve Miller on 6 Aug 2020
I have rebuilt your model with some modifications and attached it to this answer.
Some notes:
1. You can measure the wheel speed with an Ideal Rotational Motion Sensor. You can also simply view all the Simscape simulation results in the Simscape Results Explorer, which means you do not have to have extra sensor blocks in your diagram
2. I put a transfer function in to smooth the application of pressure to the Disc Brake.
3. You can enable thermal effects in the Disc Brake, which would allow you specify lookup tables for the static and coulomb friction values as a function of temperature. You could vary the temperature of the brake to get different behaviors.
4. Another option for varying friction is the Loaded Contact Rotational Friction block.

Gal Shraiter on 7 Aug 2020
That's super interesting. Continuing that, is that why you also used a step function? so the transfer function will have a sudden but smooth impact?
Also, I can't find this exact transfer function, is that taken from the default simscape library?
Thanks!
Steve Miller on 7 Aug 2020
I used the Step input block as it is convenient to specify when the transition will take place. The transfer function provides a convenient way to control how rapid the change is.
The Transfer Function block is a Simulink block. The same thing could be done within Simscape, but since this is essentially a control signal, it was OK to do it in Simulink.
Gal Shraiter on 7 Aug 2020
Got it. Thanks. Is there a way to control when it takes place when using a constant as I did before?

R2020a

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