Front and rear tire friction lines don't align with constant acceleration lines

[JonatanGeb]

Hello

I downloaded the script and tried to play around a little with in order to get a better view of how we should set up our brake system in or FS car. However, while comparing to other sources something with the script does not add up.

According to what I can find the tire friction lines (uxf and uxr) should coincide at the optimal distribution curve and the constant acceleration line. So, for example the lines from uxf = uxr = 0.7 should coincide where the line for 0.7g's of brake acceleration would be. Also this should be right where the ideal braking curve is.

I tried setting the air density to 0 in order to zero out any speed-related terms, only considering "pure braking" without any aero-effects. The ideal brake curve is perfectly in line with my hand computations but the constant friction lines do not behave according to the theory. I am no matlab expert, but I tried checking your formulas for the constant friction lines and compared them to different other sources and they seem to be fine. Additionally, I have verified that for the uxf lines the point of intersection with the Y-axis has the correct value. That leaves me believing that somehow, the slope of the lines is incorrect although the math behind them seems to be okay.

Have you run into this issue and what is your opinion on it? Is there a way I can try to look at it myself? Any help or suggestion is very much appreciated!

Best,
Jonatan

[JonatanGeb]

Here is a better picture with some more values. The way the uxf and uxr lines are as seen in the picture included in your download I cannot make them make sense. However,they make perfect sense when aligned as in the attached file according to me.

[luisdamed]

Hello! @JonatanGeb
Thanks a lot for opening this issue and taking the time to verify the math behind the equations.
I have looked at the plots generated like you mentioned, setting air density to 0 and plotting only constant mu values. They do not make sense.

Unfortunately, I didn't have enough time this weekend to dive deeper into why that is, but I think we should rule out any axis scaling from Matlab that could be causing this unwanted effect.

If I have time this week I'll try to verify that the plotting is done on the desired axes object. You could try having a look at the values from the array of constant mu values used for plotting and check if they make sense or, like you said, the slope is somehow wrong.
If the values make sense, then it could be a plotting issue.

Sorry for the inconvenience.

Luis

[JonatanGeb]

Hello

I'm sorry for the long delay. looked into your suggestions today and this is what I found. Note that I am very inexperienced with matlab and that I very well could be missing something obvious or could interpret some things wrong.

This is with a fresh copy of your script, nothing changed. The numbers in the command window seem to represented in the plot and scaled correctly. I can however only see the values for the first plot ux1 = 0.2. I tried "Show all properties" and this popped up "Unable to display properties for variable Const_ux1 because it is not scalar." This applies to ux2 as well. I might be mistaken but I think that the friction lines do not intersect correctly. They do not seem to form a curved curve, as there looks to be a "dent" where it goes from 0,0 to 0.4,0.4 to 0.6,0.6, additionally, intersections do not intersect with acceleration lines and seem to align with higher velocity curves rather than lower velocity ones. So, I believe setting density to zero does not cause the problem. I am not complaining by the way, I can use the script anyways for my calculations. Sometimes the friction lines just get a bit confusing and it might be an easy fix for someone who knows what he is doing ;)

This is with air density = 0. It seems that the friction lines are very close to each other, but their values (for the first line at least) correspond to those seen in the command window. Does this mean there is a mathematical error?

Thank you for your time!

Jonatan

P.S. I might as well take the opportunity to ask if the function to visualize a pressure valve as seen on your website is supported in the downloadable script?