+ Reply to Thread
Results 1 to 10 of 10

Thread: CoG of human body

  1. #1

    CoG of human body

    Hello FSAE world

    My name is Stefanos Stamoulis, i am part of TEIWM Racing Team from Western Macedonia, Greece. I would like to ask, if anyone in FS has calculated the center of gravity of the human body/driver and if it is necessary to do it.
    The guys from the University of Western Macedonia which participated in the MotoStudent told us that is absolutely necessary

  2. #2
    Senior Member
    Join Date
    Oct 2008
    Location
    Raleigh, NC
    Posts
    232
    Hi StefStam!

    I am sure that some FS team has measured their driver's CoG.
    Easy enough with a fulcrum and a beam for the driver to lay on.

    But what do you think?
    You should have some idea for the driver's COG.
    But how accurate do you think you need to know their CoG?
    +/- 0.5mm? +/- 50mmm?
    Do you think you could model it in CAD to make an estimation?

    -William

  3. #3
    Quote Originally Posted by StefStam View Post
    Hello FSAE world

    My name is Stefanos Stamoulis, i am part of TEIWM Racing Team from Western Macedonia, Greece. I would like to ask, if anyone in FS has calculated the center of gravity of the human body/driver and if it is necessary to do it.
    The guys from the University of Western Macedonia which participated in the MotoStudent told us that is absolutely necessary

    Find the three heaviest components on your car. These will dominate your mass distribution in X,Y,Z.

    Usually in this order:
    1) Driver
    2) Engine
    3) Chassis tubing/panels

    When you consider the "95% Average Human Male" weighs about 100 kg and an average SAE car weighs about 185kg without driver -- yes, it is absolutely necessary.
    Even the 50% Average Human Male weighs 78kg...

    Reference this document for some guidance.
    http://www.ergo-eg.com/uploads/digi_lib/116.pdf

    I would also suggest to find the CG of your drivers in their seated position either in the car or by seating them on scales in X,Y and Z. You can tilt test your drivers too.
    We found that our CG in X varied up to about 2.5% of F/R depending on who was seated in the car, our lay down style seating contributes to this significantly.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  4. #4
    Absolutely necessary and fairly straightforward. You'll need to put the driver in a seated position resting across two scales to get the x location, then rotate the whole assembly around y while the driver holds still to change the axis and allow you to get the z location. At A&M we tried to test y-location and found values that were clearly smaller than measurement uncertainty, concluding that our mass is fairly well centered laterally.

    If you'll accept my sounding like Claude here, 100 kg is clearly excessive for the mass of the driver and he or she would have to be spectacularly good behind the wheel to make up for it. Even Travis Renegar, who is larger than Percy, got down to 83kg to race. Try Ultimate Frisbee or running and eat more sweet potatoes.
    Charles Kaneb
    Magna International
    FSAE Lincoln Design Judge - Frame/Body/Link judging area. Not a professional vehicle dynamicist.

  5. #5
    What I learned from working with sport doctors and engineers working on racing crash test simulation is that in the usual driver position ("bath tub"), the human body CG is not far away from the spine 2nd lumbar.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  6. #6
    Junior Member
    Join Date
    Jan 2009
    Location
    South Dakota
    Posts
    28
    I ended up buying a very cheap student license for Catia v5 to make use of their "Human Builder" for solving this problem. The basic driver model we were using in Solidworks worked fairly well for packaging and light ergonomics, but the mass properties were a shot in the dark. I seem to remember just manipulating the density of the driver model until it matched the driver mass we anticipated... a pretty terrible way to represent the variable density of a real human.

    I ended up exporting the posed solidworks driver into catia, and then "built" a human until the Catia Manikin was aligned with the old driver. I then copied the CoG and Moments of Inertia from the Catia human (which does account for variable density inside a human) back into the solidworks model and locked the properties. Moving the Manikin into the right position using Catia's simulation of biological joints was very interesting. Driver ergonomics seem much less abstract after that exercise.

    Anyways, this revision ended up moving the predicted cg so much that I had to translate the sprung mass something like 30 mm to maintain the target longitudinal weight distribution. That was quite a horrifying "adjustment" to be making in the later stages of design.


    This screencap I took during the process might give you some idea of where the CoM is for a 95th percentile driver (without a helmet on) in a FSAE cockpit orientation. This was my first experience with Catia though, so the chance that I've done something wrong is high.


    Attached Images
    Last edited by ffrgtm; 11-27-2016 at 12:34 PM.

  7. #7
    No need to obsess about it.
    Make a choice of the driver body X,Y,Z coordinates that seems logical for your simulation input.
    Then when the car is finished measure the car CG with and without driver.
    Most of the time what you measure is at the end more reliable than what you simulate.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  8. #8
    There's a joke in there somewhere about how much cojones your driver has.
    Dunk
    --------------------------------------------------------
    Brunel Racing
    2010-11 - Drivetrain Development Engineer
    2011-12 - Consultant and Long Distance Dogsbody
    2012-13 - Chassis, Bodywork & Aerodynamics manager

    2014-present - Engineer at Jaguar Land Rover

  9. #9
    And light brain.....

  10. #10

+ Reply to Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts