PwdRacing HEAVY Weights

[Mr. Slick]

The density of the rounds is 12.2 to 12.5 depending on the specific batch that I get the material from.

The Hotmelt sticks are 10 to 10.5 in the current batch.

The extruded flat pieces are 12.0 from the second experimental run. We should be able to hit the 12 to 12.5 range with the production runs also.

The 3/8" round rod is at the 11.8 to 12 range currently. This should go up to the 12 to 12.5 range with regular production.

[FatSebastian]

What are the units of density for the aforementioned numbers? I was thinking the density of solid tungsten is only ~11.2 oz/in^3.

[Mr. Slick]

Relative Density being a ratio, has no units. . . . Specific Density is relative to water.

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http://en.wikipedia.org/wiki/Relative_density" target="_blank

Relative density, sometimes called specific density, is the ratio of the density of a substance to the density of a given reference material. If a substance's relative density is less than one then it is less dense than the reference; if greater than one then it is denser than the reference. If the relative density is exactly one then the densities are equal; that is, equal volumes of the two substances have the same mass.

Relative density is a generalization of, or in some usages synonymous with, specific gravity (which specifically means relative density with respect to water), with the former term often preferred in modern scientific usage.

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The method used in the lab is ((mass in grams) / (volume in cubic cm) )/(1g/1cc) which when used as a ratio with water gives no units . . . .

PURE W(aka Tungsten) has a specific density of 19.25 but the cubes and rounds that are commonly available have a density of 18.1 to 18.2 (based on lots of samples that I have tested)

Pb(aka Lead - Latin:plumbum) has a density of 11.3

[FatSebastian]

The density of the rounds is 12.2 to 12.5 depending...

Relative Density being a ratio, has no units. . . . Specific Density is relative to water.

Gotcha, the earlier post didn't say specific density or relative density. Thanks.

[Mr. Slick]

Here is the latest "Family Photo" that shows most of the shapes.



Here is a very short video of a couple of boys cutting the material.

http://www.pwdracing.com/videos/cutting_demo640.wmv

The density of the Adjustment Line checked out again yesterday at a 12.5 specific density. Production is ready to really spool up!

http://www.PinewoodGravity.com is where they can be ordered.

[gpraceman]

Have you given thought to making incremented weights, like these lead ones?



It is real easy to snip off the amount of weight needed, since they are marked in 1/4 oz increments. Then just peel off the backing on the adhesive tape and stick to the car. A Heavy Weights version of this would be mighty handy, especially for last minute weight adjustments.

[Mr. Slick]

The Heavy Weights can all be cut/carved/drilled/sanded to desired shape/size/weight. The material that is currently available is the "12.5 density" compound. To calculate the amount needed use the volume in cubic centimeters times 12.5, following:

Rectangle shape: Width(cm) X Height(cm) X Length(cm) X 12.5 = Mass(g)

Round shape: 3.1415(pi) X Diameter(cm) X Diameter(cm) / 4 X Length(cm) X 12.5 - Mass(g)
(Diameter(cm) X Diameter(cm) / 4 = radius squared)

To convert to ounces: 1 ounce = 28.35 grams

I hope to see the thin slabs being used for lots of people where they want to just cut it to length for the best weight.





Take a look at a video I got at one of the local open houses of a couple of boys cutting it with a small pair of scissors.

http://www.pwdracing.com/videos/cutting_demo640.wmv

Each of the pieces weigh an ounce. They are about 1.75" long so they fit the width of the cars. I have a couple of photos of them attached to the bottom of a car too. I used the double sided 3M adhesive but most glues would work. The weights can be considered to be a plastic as far as the adhesive is concerned.





The round rods are also 1 ounce per stick and 3/8" in diameter. The initial production run of the round rods was a bit thin so I am hoping to get the next run before the Lima race. . . . we'll see.

The real thin sting like form I call "Adjustment Line" and is what I would recommend for last minute adjustments. It's weight is .035 per 1/10" which should allow for precise adjustments.

I have the product packaged by weight, not volume, so if the production run is at 12.4 density the pieces are longer by a ratio of 12.5 / 12.4 = 1.008 ==> a piece that is normally 1 5/8" long (1.625") would be 1.638" long, an additional .013" in length.

[gpraceman]

Well, what is nice about the incremented weights, is that it is a no brainer. The increments are clearly marked. No guessing, no calculating. Just weigh the car and snip off as much as you need. Since they come with double sided tape, just peel off the backing and stick to the car.

[Mr. Slick]

Things to add in the future!

The feedback was to allow the weights to be cut in any shape - so that if you have a car that gets narrow you can trim the weights to fit.

I could probably come up with a method of marking some sort of increment . . . I initially wanted to sell it as a single long strip with a ruler on the packaging that shows the location to cut it into a desired weight.


Initial feed back was that the smaller segments would be easier to use.

As far as using tape on the product, that is slated for the second year. The company already applies double sided tape to other products for adherance to metal and I am told there is a specific 3M product for the plastic/wood combination. . . . but the one for plastic/painted wood is different. Due to the variations in all of the cars I decided to let the builder attach the weights with what ever they wanted.

[gpraceman]

The feedback was to allow the weights to be cut in any shape - so that if you have a car that gets narrow you can trim the weights to fit.

Understood, but mostly what I am referring to is for those quick last minute weight adjustments. Having something incremented, easy to cut/snip and having an easy way to apply, would really help at check-in (from a race coordinator's and a racer's point of view). Of course, there are going to be people that will want to use incremented weights for all of the weighting, not just final adjustment. My kids and I have used the lead incremented weights for a few cars that we have built over the years. We double or even triple stacked the strips to fill our weight cavity.

I could probably come up with a method of marking some sort of increment . . . I initially wanted to sell it as a single long strip with a ruler on the packaging that shows the location to cut it into a desired weight.

That is a step in the right direction, but not as user friendly, of course, as having the weights themselves incremented and marked.

Initial feed back was that the smaller segments would be easier to use.

The 1/4oz increments seem to work out well. If you need less, it is easy enough to know where to trim off between the increment marks.

As far as using tape on the product, that is slated for the second year. The company already applies double sided tape to other products for adherance to metal and I am told there is a specific 3M product for the plastic/wood combination. . . . but the one for plastic/painted wood is different. Due to the variations in all of the cars I decided to let the builder attach the weights with what ever they wanted.

The lead weights just seem to use plain foam tape. I haven't seen a problem with that tape working on bare or painted wood. Of our cars, which have been handled quite a lot over the years (at workshops, Pow Wows, and as test cars at races), we haven't had any of those weights fall out. How well that type of tape would stick to the Heavy Weight material, I'm not sure, but I suspect that it would be just fine.

Just throwing out something to consider for your product line... If it is not something that you can do for this season, then maybe next season...

[Mr. Slick]

I'm looking into the marking of the material. . . had some marked with a laser! Cool to watch, slow to do. . .

I've also come across some testing that I have to get completed before the retail packaging gets completed. This is the type of testing and certifications needed prior to getting my product in the BSA stores. More paper work!

Just as an FYI/reminder: (from http://www.cpsc.gov" target="_blank)
The Consumer Product Safety Improvement Act (CPSIA) establishes specific lead limits in children’s products. Section 101(a) of the CPSIA provides that, as of February 10, 2009, products designed or intended primarily for children 12 and younger may not contain more than 600 parts per million (ppm) of lead. After August 14, 2009, products designed or intended primarily for children 12 and younger cannot contain more than 300 ppm of lead. On August 14, 2011, the limit may be further reduced to 100 ppm, unless the Commission determines that it is not technologically feasible to meet this lower limit. Section 3(a)(16) of the Consumer Product Safety Act, as amended by section 235(a) of the CPSIA, defines ‘‘children’s product’’ as a ‘‘consumer product designed or intended primarily for children 12 years of age or younger.’’