The car uses pennies for weight, which offer the best weight to value ratio of any US coin, and are conveniently .75 inches in diameter. Other US coins are odd sizes, probably related to the historical value of silver. Pennies also come in two different flavors, pre-1982 and 1982-. They are the same size, but the earlier coins are almost 25% heavier, being mostly copper as opposed to the later coins which are mostly zinc. About 30 pennies will fit across the 1.75'' pinewood body and will weight between 2.6 and 3.2oz depending on the mix of pre-'82 pennies included. BTW, there are still plenty of pre-82 pennies in circulation - a random sampling from my sofa turned up 6 among 32 pennies.
Anyway, the rough cut body below weighs 37g, but as the saying goes, "still has enough wood in it to build a sailboat". I think it would be pretty easy to get the body weight down <25g with two weight pockets for pennies so that cog can be tuned and, with proper axle and wheel prep + alignment, build a car that would be competitive in many packs. The only "extra" tool needed is a 3/4'' drill bit which is very common size and easily borrowed or purchased.
https://drive.google.com/file/d/0B_gLcb ... VdVRB/view
I'd like to offer my Penny build.
Use the long end for the front and drill a 3/4" hole behind the rear axle slot 1 1/2" deep as close to the bottom of the car that is safe. Drill a second hole as close to the rear axle slot and as close to the bottom 1" deep. Cut out a simple wedge without damaging the holes. Insert 20 pennies in rear hole and 13 pennies in front hole. Seal them up. Sand away the wood over the pennies. No part of the car will be higher then 7/8". You can drill out bottom wood if you like but it's not really necessary. This set up will give you a COG of 1" in front of the rear axle slot and a weight very close to 141.75 grams. If you're a little over there's some wood you can drill out.
That would be a Fun race. Everyone build a Penny car.
- Darin McGrew
- Pine Head Legend
- Posts: 1802
- Joined: Fri Jul 18, 2003 1:23 pm
- Location: Mountain View, CA
Another BTW, those pre-82 pennies work better in souvenir penny presses than the modern pennies that are copper-plated zinc.
But yes, pennies are easy to use, easy to find, inexpensive, and non-toxic, which makes them a pretty good weight for derby cars.
Today's penny weighs 2.5 grams .. 100 of them = 250 grams .. or = to 8.81 ounce 11.3 pennies per ounce.
50 pennies per a roll.. 6 rolls of pennies would be 250 pennies at 26.43 ounce.
I know I'm Off Topic again but this is Derbytalk and I have learned so much the past 7 years from Derbytalk. Regarding trucks, I owe a lot to Whoda.
My opinion only, pennies are not dense enough and would make a very poor choice for a truck. Any weight that is put in front of the rear axle puts more weight on the dfw and that's not good. My opinion only.
I've gotta say $3.00 wouldn't even cover the shipping for the weight. So, there is some appeal there.
But, your statement "Any weight that is put in front of the rear axle puts more weight on the dfw and that's not good" has me questioning:
where do you place your rear axle?
How tall is your rig at the rear axle?
At what point is giving up all the aero to get the weight behind the rear axle counter productive?
Do I need to build another rig?
I'm not as quick building as whoda, so these tips will likely have to be applied to next years build(s).
I'll try to answer you as best I can at this stage of my education. I'm looking forward to starting another Topic hopefully in June.
Rear axle is 1 5/8" from rear of truck. Bottom of board is angled as much as I could to clear the curve of the best track.
Height at rear is 1 1/2". That area holds 6 - 2 ounce blocks (12 ounces). no weight added in front of rear axle. Truck weighs 8 ounces without added weight. Presently 20 ounces and there will be one more plate added that will weigh about 2 ounces.
Aerodynamics is not very important. What the Aerodynamics weighs is what is important. Because of the minimum length (17") you are going to have a lot of weight in front (probably). No matter how you try to tune the truck if the front is heavy (7 ounces) the Dfw is going to go into the rail hard. I will learn more this summer and am eagerly looking forward to it.
No, don't build another rig. Whatever happens it will be a very educational experience. Whatever you do make certain your front and rear wheels are close enough to the ends of the truck so the truck clears the Best track curve without hitting it.
See you at the races.
2 oz tungsten blocks. Where did you find those? What are they like 1" cubes ?
They measure 1/4" x 1/2" by 1 1/2". They do not reach my rear axle by 1/8". Originally I needed to move the rear axle forward to get what I needed. Fortunately the very rear of the truck clears the curve.
Please check your email.