Unrealistic braking distance observed in ABS model

Hi everyone,

I’ve built an ABS braking system model in Simulink to compare ABS vs non-ABS performance.

The model runs fine, but the stopping distance always shows 916 m, even after I changed the parameters.

Model summary:

v0 = 22 m/s

m = 1200 kg

I = 2 kg·m²

r = 0.3 m

g = 9.81 m/s²

The model computes slip as (v – ωr)/v, and integrates v to find stopping distance.

However, the scope still shows 916 m, which matches the result when m = 5 kg and I = 5 kg·m².

So I suspect some constants inside my model are still using the old values.

What I’ve checked:

Updated all workspace variables (m, I, r, etc.)

Pressed Ctrl + D to update the diagram

Looked inside the blocks, but the result didn’t change

What I need help with:

How to make Simulink use the updated workspace variables

How to confirm if any block is still using hardcoded numbers (5, 5)

Whether there’s a unit-conversion gain (×1000) on the stopping-distance output

I’ve attached my ABS.slx file for reference.

Thanks in advance!

[Sam Chak]

Hi @Saiganesh

With your parameters, the 1.2-tonne vehicle takes approximately 36 s to stop, covering about 1427 m. If you want to investigate, please post the full ABS differential equations so we can run a analysis in MATLAB as well as verify the Simulink model construction.

Answer 1

[Anmol]

Hi Saiganesh,

I understand that you are trying to a run a Simulink model to compare ABS vs non-ABS performance. The answer is not updating after the updating the workspace variables.

For troubleshooting the issue:

1. You can clear the MATLAB/Simulink cache using

clear classes

Clear the old declarations and define the new variables:

clear m I r v0 g;

The set the new values. Followed by model re-evaluation using the command:

set_param(gcs, 'Dirty', 'on');

Then update and run the model.

2. You can go to Modelling - Model Explorer - Model Hierarchy, then the block you want to check. You can check the block parameters and the values from there.

You can refer to these:

https://www.mathworks.com/help/releases/R2025b/simulink/ug/change-model-workspace-data.html

https://www.mathworks.com/help/releases/R2025b/simulink/ug/create-edit-and-manage-workspace-variables.html

I hope, it helps.