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Newbie Weight question

Discussion in 'Building tips' started by 408hounds, Mar 3, 2014.

  1. 408hounds

    408hounds Bent Axle

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    I am help building my daughter's first derby car and need you guy's expertise.
    Thanks in advance.

    1. Where is the optimal COG?
    I read that anywhere from 5/8 to 1 inch in front of the rear axle.
    Should I assume the closer I can get the COG to the rear the faster it will be....obviously not too close to cause stability issues.

    2. I am using a wedge shape design with cylinder weights mounted horizontally.
    Is it better to concentrate the weights toward the center or closer to the outside (closer towards the wheels)? Or does it matter?
     
  2. Obsessedderbydad

    Obsessedderbydad PWD Royalty

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    First off, welcome to the site. You'll find more useful information on here than anywhere else.

    Your build is going to be determined by a couple factors. 3 wheel rail running (center rail), 4 wheel touching, outside rails, rear wheels cant'd, etc. Give us and idea of how you're setup so we can help.

    1. COG typically is anywhere from 0.5"-1.0", and you're correct, the closer to 0.0" the faster, but less stable and vise versa. Below is my sons car he won his Den and Pack with. It has a COG of 3/5" and steer of 4" over 48" (Changing it to 5" over 48")

    2. Wedge is a good design and in PWD races, are usually the fastest. IF you're running a Cant'd 3 wheel rail runner, you'll want more weight on the DFW (down front wheel) side of the car. Depending on how much weight you have I'd run 3 of those tungsten cylinders in the rear spread evenly apart. Then, if you have a weight pocket in front of the rear wheels, put more on the DFW side. Again, this depends on weight pockets, options of where you can put the weight and your design. Give us some more about your build so we can help further or pictures would help even more! Also, you can check out 5kidsracing website for more useful information.

    [​IMG]
     
  3. 408hounds

    408hounds Bent Axle

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    Thanks for the info.! Very usefull info....my car weighs .8 oz and wheels and axles put another .5 oz on her for a total of 1.3 oz for the car, wheels and axles I have one horizontal holes for weights behind the rear and 2 horizontal holes in front on the rear wheels. How much extra weight should I put towards DFW side? Thanks
     
  4. 408hounds

    408hounds Bent Axle

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    BTW the rules are typical BSA Rules Standard 4 wheel touching, center rail. Also many oz do you add for basic painting? .2 oz?

    [​IMG]

    [​IMG]

    [​IMG]

    Car is weighting .8 oz now.
    Should I continue to make design changes to her?
     
  5. Obsessedderbydad

    Obsessedderbydad PWD Royalty

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    Honestly for a scout race it'll be awesome. Great design and should be fast. It's not the wedge shape I was thinking. My son's car weighed .5oz which was a little heavier than our NPWDRL car, but it was fast. Just make sure you get to 5 oz. I've never used tungsten cylinders so I'm not sure of their weight. If you can add more weight, add it to the rear, as much as possible. Next time, for more speed, drill your axle holes and do a 3 wheel rail runner with cant'd rears and that thing will.be smokin!
     
  6. slingblade

    slingblade Pinewood Ninja

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    I'd try 3-cylinders=1.5oz behind the rear axle.... 3 more right in front of he axle then fine tune the rest in the other hole ... Best you can do at this point
    If you can leave your vanity at home ...do just 1-2 light coats of rattle-can paint just to give it some color and add every ounce of tungsten you can
    The paint weight will cost you speed with what you have
    Next time grab a DD4 block with proper pockets to start with .... use tungsten cubes
    For now run what you have... Read this forum and the rest will come to you with practice
     
  7. slingblade

    slingblade Pinewood Ninja

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    To clarify = each tungsten cube is .5oz and three wil fit across the width of the car
    Order them from Jonh =DD4 hire
    You'll be all you can be !!
     
  8. slingblade

    slingblade Pinewood Ninja

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    Also get some tungsten putty for fine tuning after paint
     
  9. 408hounds

    408hounds Bent Axle

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    Thanks for all the info guys!

    I added 1.5 oz (3 .5 oz tungsten cylinders)to the rear and another 1.5 oz (3 .5 oz tungsten cylinders) right in front of the rear and another 1 oz (2 tungsten cylinders) to the futher most right side.

    I have a COM of 1/2 inch in front on the rear axles before axles and wheels.

    I was able to sand the car and polish the wheels down and now have a total weight of about 1 oz.

    I have a car weighing 5 oz exactly before painting.
     
  10. 408hounds

    408hounds Bent Axle

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    So more questions guys.

    Getting a little OCD...daughter wants a fast car and will just paint it with a spray can

    1. Should I center the rear weights (leftmost) behind the rear axle?

    2. How much weight should I place towards DFW side? .5 oz

    I assume I load more weights towards that side and the weights will not be centered in front on the axles.

    A. Do I put more weights towards that side by 3mm or so?

    B. Do I do this for weight cut out just in front of the rear axle or the furthest towards the right or both?

    3. Do I try to align the rear axles straight?

    4. If my DFW is on right side, should I try to bend the axle with the a little toe out?

    5. I will try to raise my left wheel but should I keep that axle staright

    I think I will be pretty lucky if i can align the axles straight truth be told. I have no idea how to bend axles and will just try to bend with a straight nose plier
     
  11. plhiatt

    plhiatt Rail Runner

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    I think he had to have 4 wheels touching,
    How do you rail ride with that, or tune it? One wheel would have to still be up
    wouldn't it? Just barely?
     
  12. Obsessedderbydad

    Obsessedderbydad PWD Royalty

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    DO NOT GLUE THE WEIGHTS IN AT EXACTLY 5.0oz BEFORE PAINT! Just wanted to post that before I answered your other questions.
     
  13. Obsessedderbydad

    Obsessedderbydad PWD Royalty

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    1. Should I center the rear weights (leftmost) behind the rear axle? Yes put the rear weights evenly in the back

    2. How much weight should I place towards DFW side? .5 oz It doesnt have to be an exact amount, but you want more weight on your DFW side.

    I assume I load more weights towards that side and the weights will not be centered in front on the axles.

    A. Do I put more weights towards that side by 3mm or so? Same as above, center the weight in your pocket right in front of your rear axle (middle hole) then put weight on your right hole towards the DFW side.

    B. Do I do this for weight cut out just in front of the rear axle or the furthest towards the right or both? Not sure what you're asking here.

    3. Do I try to align the rear axles straight? Since you dont have the rear wheels cant'd your only option is straight.

    4. If my DFW is on right side, should I try to bend the axle with the a little toe out? Bend the axle at 2-3 degrees and use that as your tuning axle.

    5. I will try to raise my left wheel but should I keep that axle staright. Your rules say 4 on the floor, so your only option here is to raise it just enough so the inner edge of the wheel is touching to still be considered legal.

    I'm going to have to pass this off to a professional because I worry with a 4 on the floor, non cant'd setup and a COG of 0.5" might be a little aggressive. You can usually counter this with steer, but not having the rears cant'd and having the the other front wheel touching may cause some issues for steering. Ive never ran a 4 on the floor setup. I only said dont add weight to exact 5.0oz b/c paint will add weight. Stay under, like 4.75oz, then use the tungsten putty to make up the extra weight.
     
  14. DerbyDad4Hire

    DerbyDad4Hire Administrator Staff Member 25+ Pro Race Wins! National Champion

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    Actually, press the rears in and give them a negative cant in the slot. You will have to eye ball it to make sure they are the same. Do a small bend on the front 2 axles trying to make them the same degrees. Insert your dominant side first and tune it to get a steer of 3" over 4' making sure it is in a positive cant. Once you have it steering right add the 4th wheel so it steers with the other front wheel but barely touches and does not change the tune of the car.
     
  15. Obsessedderbydad

    Obsessedderbydad PWD Royalty

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    Thanks John
     
  16. slingblade

    slingblade Pinewood Ninja

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  17. OPARENNEN

    OPARENNEN National Contender Pro Race Winner National Champion

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    IMO the further weight is to the bottom and back of the car, the better.
    I make my finished cars intentionally a bit light, then I glue or tape a piece of 1/16th lead on the bottom.
    You can buy sheet lead (1/16, 1/32 & 1/64) in several places (including internet), and it cuts with scissors.
    By doing this, you can even shape the bottom lead piece to put more weight on one side or the other.
    And if you have a track, you can move the bottom piece forward or aft to get the COM you desire.
    However, I seldom pay any attention to the COM. I just put all the weight as far back and low as possible, and test the car, and changing the steer to get the beSt time, and to eliminate wobble.
     
  18. 408hounds

    408hounds Bent Axle

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    Thanks again everyone.

    I did change my COM a little to move it forward to 5/8-3/4 inch.

    I really don't have the a lot of time to test the car before hand since we only have an hr time to check in the cars.

    I really do appreciate everyone's help.

    This means a lot to me and my daughter as she drew out the design on paper and is excited to paint the car. I asked her if she wanted something pretty or fast. Of course she wanted fast!

    My daughter has been very sick for the past 2 1/2 years and is just finishing up her medical treatment.

    This is one of the first times she has been well enough to even do anything like this.

    Really appreciate all the wonderful advice!
     
  19. IAE Racing

    IAE Racing PWD Royalty Pro Racer

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    Our thoughts and prayers are with you. keep up the good work and Good Luck!
     
  20. aircooled

    aircooled National Contender

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