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Weight Distribution

Discussion in 'Building tips' started by mitso, Mar 14, 2017.

  1. jatofau1

    jatofau1 Council Champion

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    I use three separate scales. I put one under each rear wheel and the third under the DFW. Note the scale weighing surface all need to be at the same height so it is best to have three of the same scales.
     
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  2. derbydentist

    derbydentist Council Champion Pro Racer

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    Aha! So simple and yet to ingenious for my brain to work through on my own - thank you!
     
  3. davet

    davet League Racer

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    We use 2 identical scales to measure rears then just flip the car around to measure the DFW. You can use one scale as long as the car is level.
     
  4. Crash Enburn

    Crash Enburn PWD Royalty

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    The easiest is to use three scales, one under each wheel. Or, using a single scale, build up a stack of books or something near the scale so that it is level with the surface of the scale and then weigh the car three times, with a different wheel on the scale each time.
    Oops. Didn't see that we were at the bottom of page 1 and there was a page 2. :eek:

    Personally, I believe this to be much ado about nothing.
     
  5. davet

    davet League Racer

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    I think experienced builders wouldn't use the weight measurements. We only built a few cars and having those weights recorded helped us to get close to what we had the year before and helped us know if we were setup more conservatively or more aggressively than the previous car.
    It helped us decide to add cubes between the rear axles in order to get a better COM than we had previous yrs.
     
  6. derbydentist

    derbydentist Council Champion Pro Racer

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    Excellent thank you so much for clarifying all this for me!
     
  7. B_Regal Racing

    B_Regal Racing PWD Royalty Pro Racer

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    Not sure if I would consider myself experienced, but I absolutely use three identical scales to get the weight on wheels. I have no interest in COM whatsoever, but it can easily be calculated if you have the weight on wheels. I don't use COM because I am not only looking for a front to back COM, but a side to side COM as well. The weight on wheels will tell me everything I need to know.
     
  8. Crash Enburn

    Crash Enburn PWD Royalty

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    I balance my car on my fingertip to find my exact (horizontal) CoM. YMMV.
     
    Last edited: May 5, 2017
  9. mitso

    mitso Bent Axle

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    Hi Derbydentist, I just noticed your question on the post.

    B_Regal posted a great answer for this -
    I only have two scales but am ordering another one. In my case, I use two scales to measure the weight under each rear wheel and keep the front of the car level using a stack of business cards.
    The scales are identical, and as mentioned three would be best.
    After measuring the rear weight distribution you can move a scale under the DFW and obtain that weight. I also rotated the car (place the rear of the car on the stack of bus cards) and measure the weight of the DFW.

    A key step is to check that the measuring surface is level. Definitely take a few measurements to verify your setup and cross check that all of the measured wheel weights add up to the total weight of the car.

    The link that I posted is for a site that you can use to enter the dimensions of the car, along with the wheel weights, and obtain a computed COM both front to back and side to side. I also check using the cantilever method and the two measurements were very close. That said, I don't have a bullet proof cantilever method to get the COM of a car, i.e., having the car balance perfectly and having the rear wheels perfectly parallel.

    The more experienced builders, like B Regal, Crash Enburn, etc. know what is best for their car and track, etc. I am just learning :)

    dah, just found page two of the post. Sorry to repeat what others said.
     
    Last edited: Apr 14, 2017
  10. gdurban

    gdurban District Champion

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    I use 3.
     

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  11. txchemist

    txchemist National Contender

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    Here is a different way to come close on balance

    [​IMG] 5ozcar.jpg
     

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    Last edited: Dec 21, 2017
    M Tull and gdurban like this.
  12. HurriCrane Racing

    HurriCrane Racing PWD Royalty Pro Racer 25+ Pro Race Wins! National Champion

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    That is an interesting way to weight a car. The weight blocks look pretty cool!
     
  13. txchemist

    txchemist National Contender

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    Thanks!, I use a bit of aluminum tape on the block where I epoxy it in so I can get it back out without too much work. I find that after the epoxy dries, that wood around the axle area is held super straight and I then drill the axles. I use the Silver Bullet Pro and have not had a bad drill since doing it this way.
     
  14. racingron

    racingron Lurking

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    Where do you get the weight blocks you are using?
     
  15. txchemist

    txchemist National Contender

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  16. racingron

    racingron Lurking

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    Ok, thanks!
     
  17. Derek Konrad

    Derek Konrad Hammering Axles

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    Hey Guys, attempting to figure this out. Looks like from the post and pictures that the ND Rear Wheel needs to be heavier than the D Rear Wheel. Do I have that right. Is there some logic to this approach?
     
  18. TRE

    TRE PWD Royalty Pro Racer Pro Race Winner

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    Some like to have them even
     
  19. Vitamin K

    Vitamin K District Champion

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    This is a natural condition that arises when you have a lifted front wheel. The rear wheel behind your lifted wheel is going to carry more weight than the rear wheel behind the track-touching (DFW) wheel.

    Some people will bias the weight of the car to even this out a bit. You can play with Minion Racing's calculator to see what weight is required to get the car's side-to-side center of mass balanced.
     
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  20. cmoney atrain

    cmoney atrain Pinewood Ninja

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    So I see that TxChemist tried to even out the weight on the rear wheels by moving it closer the the DFW side. This natural condition, as explained by Vitamin K, of one rear side weighing more than the other, should be mitigated by placing more weight on the other side. (?) Is it possible to achieve a perfect balance?

    Also, is it your experience that with all other items being equal, a balanced rear will run faster than a non-balanced rear?
     

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