Physics Spreadsheets FAQ / Q&A thread

Discussion in 'Car Modding' started by thoraxe, Jun 7, 2018.

  1. thoraxe

    thoraxe Registered

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    This thread originally started as "are there example spreadsheets other than the FISI?" and it has turned into a detailed FAQ on how to use the physics calculator spreadsheet.

    Latest spreadsheet here:
    https://docs.studio-397.com/developers-guide/cars/car-physics/physics-calculation-tool


    Q: My car has no real aero (no diffuser, no front or rear wing). What do I do?
    A: Put in comment or Delete the entry in the HDV (the blocks FRONTWING, REARWING, DIFFUSER, FENDERS if any).

    Q: The cartesian coordinates are in reference to what? As an example, when I set X to 0 for the front wheel upper front arm, I see where it ends up in the diagram, but what actually is "0"?
    A: With help from Devin on Garage discord (https://discord.gg/q9FVQc3):

    So my interpretation/paraphrasing:
    • Z is the front-back axis of the car (along center line from absolute center)
    • Y is the up-down axis of the car (height above ground)
    • X is the left-right axis of the car (distance from center line)
    • all in reference to the absolute center of the vehicle
    Q: On the Susp tab, what is "pushrod"? In my particular vehicle case, I have a standard coilover shock and spring where the upper is mounted to the chassis and the lower is mounted to the lower control arm. Are these the "pushrod" measurements?
    A:
    Q: What is the best way to measure a real car to determine the cartesian coordinates (X,Y,Z) of the various suspension pickup points and arms? My best guess right now is to quite literally put the car on a giant piece of graph paper and determine the vehicle absolute center (X=0,Z=0) and then use a plumb bob to measure Y for each point in space. Is there a better/easier way?
    A:

    Q: On the "Spring" tab, what if I don't want to use N/m for the spring values?

    A: Starting on Row 65 there are some spring configurations.
    • You can change the unit to kgf/mm
    • You can change the min/max values
    • You can change the steps
    The values in the dropdown (B34/B10) don't end up getting updated to the stepped values, though. They're still showing the calculated SI N/m values, which is not fun. But you can do the math to figure out what you should choose in the dropdown.
     
    Last edited: Jun 16, 2018
    patchedupdemon likes this.
  2. Jokeri

    Jokeri Registered

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    No shortcut to happiness mate, you need to have realworld measurements/data. Sheets are all the same just with different numbers.
     
  3. thoraxe

    thoraxe Registered

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    I'm mostly trying to figure out what to do with a wingless/undertray-less car on these sheets.

    It definitely would be awesome if there was a "simplified" sheet where you could enter much more basic information for getting started.

    But, I'll just have to plug away at it.
     
  4. thoraxe

    thoraxe Registered

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    Is rF2-Physics-Calculator-V0.22-FISI-2012.ods the latest version?
     
  5. thoraxe

    thoraxe Registered

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    OK, after digging in a bit, the fact that the example spreadsheet is for a Formula car and I'm doing a tintop / standard sedan means there's a lot of quite ridiculous values. Understanding how to back these out for "my" car is going to be quite difficult.
     
  6. thoraxe

    thoraxe Registered

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  7. thoraxe

    thoraxe Registered

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    Working on my JZZ30 Toyota Soarer/SC300 physics spreadsheet:
    https://www.dropbox.com/s/728725dhzybz1yk/rF2-Physics-Calculator-jzz30-V0.33-v0.1-180608.ods?dl=0

    The car has no undertrays/diffusers and currently has no wings.

    How do I "disable" those features of the spreadsheet? Or do I just delete their entries out of the HDV file and mostly leave whatever?

    There are undertray properties on the "General" tab and then five or six sections on the "Aero" tab, some of which are wings/diffusers/fenders.

    Again, a regular sedan example spreadsheet would be immensely useful here.
     
    Last edited: Jun 9, 2018
  8. MaD_King

    MaD_King Registered

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    Put in comment or Delete the entry in the HDV (the blocks FRONTWING, REARWING, DIFFUSER, FENDERS if any).
     
  9. thoraxe

    thoraxe Registered

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    That's awesome, thanks!

    I sent these questions to @Michael Borda but I'll also put them here:

    * The cartesian coordinates are in reference to what? As an example, when I set X to 0 for the front wheel upper front arm, I see where it ends up in the diagram, but what actually is "0"? Or are the 0s essentially arbitrary? It's easy for me to measure the arm lengths, but not so easy to figure out how to relate them to these coordinates.

    * What is "pushrod"? In my particular vehicle case, I have a standard coilover shock and spring where the upper is mounted to the chassis and the lower is mounted to the lower control arm. Are these the "pushrod" measurements?
     
  10. thoraxe

    thoraxe Registered

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    Answering my own question about the coordinates with help from Devin on Garage discord (https://discord.gg/q9FVQc3):

    So my interpretation/paraphrasing:
    • Z is the front-back axis of the car (along center line from absolute center)
    • Y is the up-down axis of the car (height above ground)
    • X is the left-right axis of the car (distance from center line)
    • all in reference to the absolute center of the vehicle
    Hopefully this helps others.
     
  11. thoraxe

    thoraxe Registered

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    Current/remaining questions:

    * On the Susp tab, what is "pushrod"? In my particular vehicle case, I have a standard coilover shock and spring where the upper is mounted to the chassis and the lower is mounted to the lower control arm. Are these the "pushrod" measurements?

    * What is the best way to measure a real car to determine the cartesian coordinates (X,Y,Z) of the various suspension pickup points and arms? My best guess right now is to quite literally put the car on a giant piece of graph paper and determine the vehicle absolute center (X=0,Z=0) and then use a plumb bob to measure Y for each point in space. Is there a better/easier way?
     
  12. Michael Borda

    Michael Borda Car Team

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    Yes, pushrod is just the damper/spring connection (the name is a little misleading, I'll admit).

    If the car is symmetrical (which is generally the case), it's often easiest to measure the precise distance between 2 co-ordinates. Once you have a point, you can always measure relative to that point. The 'Z' co-ordinates, don't necessarily have to be from 0 either, the most important is to make sure your points are correct relative to the wheel centre.
     
  13. thoraxe

    thoraxe Registered

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    The recommendation in The Garage discord was to actually just measure everything from the spindle/hub, and then put that into Blender. Then, knowing the wheel base and the track I can actually just do simple math to calculate the distance from center. That *should* work.

    If I can borrow some hub/wheel stands I can keep the car at ride height but with the wheels off, which means I can then measure the suspension more easily. Thanks for the suggestions.
     
  14. thoraxe

    thoraxe Registered

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    Added some information on spring rates and updated with some answers from Michael.
     
  15. LoSte7

    LoSte7 Registered

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    Hi Micheal,
    i 'm just looking in to forum to find someone can explain me about pushrod position, and i think you can help me a lot.

    in my case i need to create a mod of a formula car, with pushrod, but if i well understood, when i model the suspension in rF the pushrod are just the connection between wheel and spring, so i don't have to put in the real coordinates of pushrod as the other arms right? i just have to find the best coordinate that replicate the motion ratio between chassis and wheel, am i right?

    thanks for your help
     

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