|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
64.12.116.6
My 9 year old and I are building his Cub Scout Pinewood Derby car again. The cars are 7” long and the kit comes with a wood block, 4 plastic wheels and 4 nails for axles. The track is 50 feet long, part of which is down hill. A ¼” guide strip keeps the cars in their lanes. This is posted for your interest in the engineering.This is what we have done to the kit.
True the wood block and cut down to ½” high. Cut into a highly aerodynamic shape. Remove substantial weight from the front. Weight the back with hot lead in front of and behind the rear wheels. A good portion of the mass is centered on the rear axles and the center of gravity is low for increased stability.
Drill the axle holes on a 5 degree angle so the wheels ride on the inner edge, this reduces rolling friction. Move the wheels to the 4 corners of the car. The right front wheel is raised to not touch the track for less friction. The wheels are trued , bores polished. Balanced, and graphite coated.
The axle nails are debured, straightened, and friction reducing groves are cut in the shaft. The inside nail head is coned for less contact area against the side of the wheel bore and the nails are multistep polished to a jewelers rouge mirror finish.
Graphite-molly lube is used with the molly acting like little ball bearings.
If anyone wished we can send photos to your email.
Follow Ups:
When my son was 9 (he is now 23), we entered the Pinewood Derby. Looking for the easy way out, I took the block of wood and created a simple wedge shape with no embellishment, using a saw. We attached the maximum allowable weight, glued to the slope of the wedge, after applying minimal black paint to the wood. We liberally applied powdered graphite to the nail axles of the wheels which were just hammered in. No polishing or anything else. Voila! Done.
It won the Derby handily, much to the chagrin of the fathers who had done all the work, creating wood sculptures with fancy paint jobs, then claiming their sons had done all the work. Yeah, right.
I still have the trophy. Priceless.
Al, let the kid use his own imagination, provide your educated input, and let him be a kid WITH HIS OWN CAR - not daddy's - at the pinewood derby.My 1st car didn't make it down the track. My 2nd won one heat; I still have it sitting on a bookshelf, it's a great memory. I learned to do my own work, and learn from my mistakes. Earned my Eagle in '79.
The kid who always won? He was a moron, drives a garbage truck now. Daddy always made his cars fast.
The little guy uses the drill press and scroll saw, paints and sands etc. I wont let him pour hot lead and things like that. I insist on his participation and explain what parts of the engineering I can make stick. We also help others build their cars. we have built 3 and helped others with 7.It's not "here's your pimewood car, dont touch it"
Buff the nail shanks where the wheels ride. Don't reduce the diameter, just polish the marks made when the nail machine grabbed it to make the head.Just remember, get mass right to the upper limit, and reduce all other drag. Energy available is mass x gravity acceleration x change in vertical height. The only thing you have control over is mass.
Does your group have a 'Father Class'? In mine, this only used the mass limit, the wood block and the wheels. Bush the wheels, find new axles...
I remember doing that waaaaay back when and being greatly dismayed when my super-aero design was absolutely dusted by big sleds with a lot of weight in them...I don't think aero should be ignored but make sure (as it sounds you are) to focus on maximum permitted mass and minimizing rolling resistance.
Check the tracking of your car to minimize hunting left and right as it rolls down the track - as it bumps the sides (or center guide) it scrubs off speed.
Thanks Caffienator.The car is 4.99 oz. It goes so straight that it exactly stays next to a line in the kitchen floor for over 15 feet.
We just helped a friends kids in another pack and they got 2 trophies last night.
The weight in the far back makes the weight travel further down the sloped part of the track. The light front with wheels pushed forward makes for easy direction changes due to the extra leverage and low mass.
Wow and your cub scout did all that by his self?LOL pinewood derby that the windup string derby things are something for the dads to compete with each other.
My son and I built a Tomahawk cruise missile looking string racer when he was in scouts I modified the prop like we use on our control line speed planes and some other things used some competition rubber. the result was the torque was so much it wrapped itself around the string and got blown away by a brick hanging from the string LOL
funniest part is my son now maintains the radar systems on the USS Shiloh CG-67 one of the nastiest guided Missile cruisers in the Navy.
Went through this years ago when my three boys were in scouts. They collected beau coupe trophies for heats won and design. Aerodynamics are nominal given the speed and mass of the car. I suggest crafting a beautiful car that looks as nice as it is fast. This opens the door for design trophies. Be creative with the design. You can have a unique and beautiful car and still have low drag. If allowed carve the bottom of the car like a boat hull - try to reduce ground effect. If you're concerned about aerodynamics then you should be concerned about ground effect (generally the raised part of the tract if very close to the bottom of the car. Don
Ground effect is a subject I am light on. We kept the car a little less than the 3/8" minimum clearance from the track. I do seem to recall that wind resistance under a car can be higher than over the top. The stability of the car is excellent.
This post is made possible by the generous support of people like you and our sponsors: