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Help shaving .045 off Cub Scout derby times

Discussion in 'Ask The Pros' started by Dad o' Scouts, Jan 2, 2021.

  1. Dad o' Scouts

    Dad o' Scouts Hammering Axles

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    Like many lurkers turned members, I'll start by saying thank you. When my scouts started pinewood derby, they were consistently last: we hammered their wheels into the slots (then taped them into place when the inevitable breakage happened), even once ran a car with a little paint on the wheel because we applied wheels, then painted. The boys build their cars by themselves (with appropriate adult supervision and based off the model I built to satisfy my need to build, too) and have become the scouts to beat in the pack. That's thanks to the time and expertise that's been shared here.

    WHERE THEY WERE:
    Last year, they did raised wheel, 2.5-degree canted axle (Pro-Driller Tool - no check on results of drill), 5 1/8 wheel base ladder cars: (1/4 thick down to 0.4 oz including a thin sheet of balsa on top to provide platform for gluing weights). They filed 12 axles down, picked the best 3 each, and did 10 seconds per at various wet sandpaper grits (got an automotive pack and then added on 5000 or 1000... don't remember). Mothers and Pledge. Weighted to 5 with tungsten: 2 oz of cubes behind the axle and the rest in front, slightly favoring the DFW but only one scale, so no idea what the balance ended up. COG was just over 1/2" inch in front of axle. Tuned to 2" steer over 4'. Used aluminum tape to cover the body with dark black electrical tape under front. Didn't touch the wheel treads last year. Just inserted axles without measuring gaps. (A picture of the outline of my practice car is attached.)

    Track is a 35-ft Best track that's a little rough (rail riders with the DFW on the left hit a spur on the track 1/3 of the way down and jump the track). The stopping pads were worn away, so Pack used towels to catch cars.

    Their times varied. One started at 2.564, got to 2.553, and ended at 2.562. The other started at 2.563, got down to 2.541, but also went up to 2.592 and 2.570. At districts the first car placed (with times varying from 3.057 to 3.122 - don't know track type/length: 4-lane aluminum with Grand Prix timer) and the other one lost the track twice (riding sideways down the lane once and coming off the lane and smacking the timer another time).

    Our district/pack rules are box stock, truing wheels but no change in tread contact area and no "substantial" reductions in weight.

    WAY FORWARD:
    It's now the last year for one of them and they'd like to hit 2.499. Given all of the speed they left on the table last year, I'm wondering if it's possible and, if so, trying to get some help getting down there. We're going to try Bulldog's method of building fenders and buying DD4H air shields, but beyond that...

    I'm wondering:
    - Other than being much more careful with wheel gaps (and probably using glue this year), actually doing something to the wheels, and adding more steer, (EDIT: and being a bit overaggressive on weighting) anything obviously wrong with the above?
    - If I've been convinced that DD4H's SBE is superior method for drilling axle holes, is it something that scouts can use with a hand drill or will their results likely be consistent to their results with a Pro-Driller? (I admit I'm torn between buying predrilled and saving the money now that they're almost out of scouting and keeping the cars as they were the past year: entirely scout-built and out of box (except for some extra stock wheels/axles to pick from) and knowing that at least the body is right).
    - Is getting below 2.5 on a wearing-down Best track possible without lightening the wheels? If so - and cognizant of the previous lathe discussions (I don't have one, though I wish I did) - is there a good way for a 10 y.o. to do it good enough for their purposes?
    - Maybe implied above, but did they go too light on their bodies?

    Appreciate any advice you can provide. I'd really like them to get faster again: they can't control what other scouts do, but they can control and improve their own work. I know they've got room to improve and I'd like to do whatever I can to help them.

    Thanks.
     

    Attached Files:

    Last edited: Jan 2, 2021
  2. OneSpartan

    OneSpartan Pinewood Ninja

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    My thoughts:
    - More steer will definitely help. If you're track is that rough I'd shoot for about 6" over 4 feet
    - You are right, the SBE will is a superior method to drill axle holes and yes, scouts can use it with a hand drill. Drill a few bodies, check the drills with pin gauges/drill blanks and 3-2-1 blocks if you have them, and go with the best one.
    - A set of trued up wheels and BSA speed axles from DD4H would be big improvements. These are stock parts but machined/improved professionally. I would think both would adhere to your rule set.
    - I would not do anything to the wheels yourself other than polishing and waxing the bores. Trying to alter an out of round wheel yourself is going to do more harm than good. See above, buy a set if you want a good set. Spend your time on the prep.
    - Fenders and air shields will definitely improve speed if done properly. I just built a fender car with my son (he's 9) and while I had good intentions of him helping, it is NOT a very kid friendly project. He helped a little bit, but it was largely a dad project. Same with putting on air shields. Both require CA glue and a high level of precision.
    - If allowed, I would shorten up the wheel base a little. 5/8" from the back for your rears and maybe 4 3/4" wheel base. It will give you more room up front for fenders too.
    - The bodies are not too light in my opinion. Gluing 1/64" ply over the weight pockets will be more rigid than using balsa though.

    As for your time question, too many variables. The same track will run very different times each set up because of hill angle, lanes not being straight, etc. Unless you run on the same track that is never taken down, you cannot compare times year over year. I learned that the hard way.
     
  3. Dad o' Scouts

    Dad o' Scouts Hammering Axles

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    Thank you! That all makes a lot of sense, including the air shields and fenders as a dad project... Will modify my DD4H shopping cart accordingly.

    Kind of glad to know times change on tracks... my kids didn't see the time improvements year-over-year they'd expected last year and I couldn't figure it out.
     
  4. OneSpartan

    OneSpartan Pinewood Ninja

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    If you get the SBE, you will not regret it. I just drilled 1/4" thick blanks for everyone in our pack that wanted one and had a lot of thrilled moms and dads.
     
  5. Dad o' Scouts

    Dad o' Scouts Hammering Axles

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    That's great. Happen to remember how long shipping took?
     
  6. OneSpartan

    OneSpartan Pinewood Ninja

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    I got mine pretty quick. Give me a shout if you have more questions.
     
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  7. Dad o' Scouts

    Dad o' Scouts Hammering Axles

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    I appreciate the help. Thanks again.
     
  8. Loud2ns

    Loud2ns District Champion

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    Shorten wheelbase
    Add steer to be at 5" over 4 ft
    Get a set of trued wheels
    Need to polish those bores. John has a great three step program. Have you polished and waxed your bores before?
    If allowed use oil process
    If graphite only...make sure to burnish the wheel bores and pledge your axles
     
  9. Mojo Racing

    Mojo Racing National Contender Pro Racer

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    Take the class I am putting on.


    I will cover everything you need to do from block to box. Showing you the processes for each step along the way
     
  10. Dad o' Scouts

    Dad o' Scouts Hammering Axles

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    Thank you. We've polished before: two different ways but both just graphite (once with cut q-tips and once using pre-graphited cotton rods from some vendor I don't remember now). Plan to try John's process this year.
     

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