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Wheelbase and COM question

Discussion in 'General Pinewood Derby Discussion' started by BobbyHamms, Jan 7, 2023.

  1. BobbyHamms

    BobbyHamms Pack Champion

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    Hi everyone, my son and I are looking to kick it up a couple of notches this year. Last year we did a simple wedge, used the standard wheelbase, along with the original axle slots and we did not make a rail rider. We did pretty well for our first outing, 2nd overall in our district. Our rules do allow for extended wheelbases, 3 wheels, bent axles, the wheels can be trued, hubs coned, but nothing beyond that.

    We are planning on making a ladder body and using tungsten cubes this time around. I made a rough sketch, with the rear axle line at 5/8”. It seemed that 5” inches forward from that axle line was a safe way to go, however, I was surprised that the front axle line was behind where the front axle slot was. Everything I had seen up to this point has suggested a longer wheelbase was faster, I would imagine it’s much more important to have the rear axle as far back as possible.

    I was thinking of shooting for a COM of 3/4”, I have heard 5/8” is fine/safe to do with ladder style cars.

    I have attached my sketch for the car, the X sections will be completely cut out.

    We are planning on running fenders this year.

    Any input/advice on my 5” wheelbase and 3/4” COM would be greatly appreciated, or is it possible to go more aggressive?

    Thanks in advance and thanks to everyone for all the great advice my son and I have already received on this forum.
     

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  2. Loud2ns

    Loud2ns Workshop Leader

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    5" wheelbase sounds good. If your track is a bit on the rough side ¾" will work. If you have a smooth track 5/8-9/16" will be better.
    Yes, but with a more aggressive car comes less stability. A wiggly aggressive car will be slower than a less aggressive stable car. Work your way up to it or you could end up with a rail banger.
     
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  3. BobbyHamms

    BobbyHamms Pack Champion

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    I agree with you, since we are trying several new things this year, it is probably best not to push things too far. I think I will stick with that 5" wheelbase and maybe push the COM a little more, I remember both the pack and council racetracks being very smooth. Thanks for your advice, we really appreciate it.
     
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  4. flockshot

    flockshot District Champion

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    I don't know what type of finish line your track uses but if it is a "crash box", like our track is. I don't know if your body will be strong enough to take the hits. You may want to consider leaving a little more strength in some areas.
    P.S. Most packs have what is called a "dad's car' or "Family car" race that is outside the scout races. This is a good place to put your most aggressive designs for testing.
     
    Last edited: Jan 8, 2023
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  5. Jupiter 2.9

    Jupiter 2.9 Council Champion Pro Racer

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    Only the front axles need to be bent “for imparting steer & lifting the off wheel”. The rears should be straight & the holes can be drilled with any jig clamped tight. Inexpensive jigs are adequate, better ones cost more. Most are already set for a canted rear angle. Search for the Lightning Boy 1,2,3 method.
    You can get aircraft length drill bit on Amazon. I don’t drill with them I use them to verify the angle of the drills.
    1st thing, watch every video on this site then ask more questions.
    Good Luck this season.
    Jup.
     
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  6. BobbyHamms

    BobbyHamms Pack Champion

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    That’s a good point and I will check with the scout master/race officials because I can’t remember what was used last year. If it is a crash box, do you think a ladder design like the 5kidsracing one where you cut out a 1/4” section across, leave a 1/4” inch section and alternate along the length of the car? I attached a photo of that particular design. Thanks for your advice.
     

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  7. BobbyHamms

    BobbyHamms Pack Champion

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    My dad was nice enough to get me the DD4H silver bullet xtreme for Christmas. I’ll look into that drill bit and I’ll check out those videos, thank you for your reply.
     
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  8. flockshot

    flockshot District Champion

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    5kidsracing knows their stuff. I would not be afraid to try anything they recommend.
     
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  9. DerbyDad4Hire

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

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    Great Christmas present! I am always available if you need help.
     
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  10. BobbyHamms

    BobbyHamms Pack Champion

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    They raise up the track at the end and it goes into a pillow, that is for the pack race. I put in an email to the race organizer for the council race, I can't remember what they had last year. Car can't be fast if it's broken!
     
  11. ScoutDadinVA

    ScoutDadinVA Pinewood Ninja

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    Hey there, could someone point me to the videos or are this for subscription only?
     
  12. Jupiter 2.9

    Jupiter 2.9 Council Champion Pro Racer

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    Go to the Forums tab & look at those items.
     
  13. T-Bone Racing

    T-Bone Racing Workshop Leader

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    When it comes to scout races and cars, strength is your friend. If all else is right, you can still win without having to cut anything out other than the weight pockets, but if you do have a ladder body, I suggest gluing a piece of 1/64th birch plywood all the way down the car and sanding it so it’s smooth and a little more aerodynamic. Many people go back and forth as to wether or not it makes a difference speed wise as oppose to just putting plywood on top of the weight pocket, including myself, but I do know it will strengthen the body enough to the point that it should withstand any hits.
     
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  14. ScoutDadinVA

    ScoutDadinVA Pinewood Ninja

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    my experiment....I glued two sugar pine blanks with opposing grain, sanded them to 1/4+inches with the joint near the top and then routered out until I hit the top layer. I know I was close once the router bit hit that top layer. I used a light next to the router table/drill press, to check how close I was. This body is now around 11.5 grams and strong!! I might take it lighter tonight. kids helped too!!
     
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