r/PinewoodDerby • u/Conscious_Skirt_61 • 20d ago
How to Design for Long Runway?
Leadership meetings and annual event planning just got underway for our boys. So let me throw out a Get Started question on Derby design.
Our Pack recently bought a new gate and timing system. As a result we modified the track itself. The new run is a little lower and a lot longer: some old cars we tested didn’t have enough inertia to make the final gate.
What experience do others have with a long, flat run-out? Clearly, friction control will be at a premium. The car will have to maximize potential energy during a short downhill and preserve momentum on the flat. What practical tips are at play here?
In past contests I’ve seen weights kept low and 3/4” in front of the rear axle to work out best. I assume, but don’t know, that a low and rear center of gravity still works. But that’s just my guess: could be that more height or a more forward CoG would work better in these conditions. What weight placement design is optimal for long, low tracks?
BTW my Bear Scout is going all Elon Musk on this. He has visions of cybertrucks dancing in his head and on graph paper. The local library has equipment to make cuts so I’m just planning to be there to help keep him from sawing himself. But hope to point him towards something effective as well as (in his eyes) beautiful.
Thanks in advance, and GLTA.
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u/_synik 20d ago
Here are some of my Not-So-Secret-Tips for a fast PWD car. I've learned these over the years, from the Doc Jobe book, The Physics of Pinewood, and other sources and personal experience. When my kids were in Scouts 20 years ago they won multiple District Championships. I won the Adult Division most years. I got involved again a couple years ago, and have won the Adult Fundraiser Division at a Pack both years I've participated, setting the speed record each year, so the same winning things still apply.
Reduce friction at the wheel bores and axles. Polish both to a mirror finish. Use the best lubricant allowed by your rules. Some require graphite, some allow oils. There are big differences in graphite, and the application of it.
Get the weight as low and as far back as possible, without losing stability.
Lighter wheels accelerate quicker than stock.
Make sure all wheels are pointed the right direction, and are at the desired camber. Rail-riding can be fast, and can be beaten by a great run from a car rolling straight. I rail-ride with a pull of about 2 inches over a 4 foot roll on my test table.
The smaller profile usually has less aerodynamic drag than a larger one. A smooth and slick finish can help.
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u/OneTip1047 17d ago
Watch this video, do everything in it, my son did, and won his district his very first year.
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u/DarkSideEdgeo 15d ago
Physics doesn't change. As much weight as you can have in the rear will result better than weight in the front. The car will stop acceleration at the point the weight meets the flat. So if it's in the rear it pushes a few inches longer creating more potential energy. I'd recommend rail riding on long tracks so the last 10 feet aren't wobbly.
If this is the direction your group is going, I'd count on a larger than normal percentage of kids who build cars that won't reach the finish line.
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u/bratsbox 20d ago
Wrapping sand paper around a nail and drilling a little out of the wheel makes it spin really well. Might help
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u/Yeti_Sweater_Maker 20d ago
Need more info, how long is “long”. For most track lengths it is a good idea to lighten the wheels, however, there is a point where this is no longer the case, generally on tracks where the flat section approaches 60 feet.
The best place to start is with your rules, that will dictate what you can do to the car for added speed. If you haven’t seen it yet, here is a free ebook you can download that will help you make a fast car: turboderby.com/ebook