Densest Building Materials

[patrickggh]

For my class, I need to know what are the densest Building materials that we can use for the drive train of a robot in the FTC game. An Help would be appreciated.

[dtengineering]

Well, I'd suggest you start by looking at the list of densities of common materials on Wikipedia. Then you can sort them in order of density by clicking on the little arrows at the top of the list.

Start at the top of the list and work your way down. The rules prohibit you from using dangerous or harmful materials, so Osmium is probably off the list. You also have to be able to find a common source of the material, "available to all teams". So unless you can find an easy way to purchase Iridium, it's probably off the list, too.

But technically, anyone can buy Platinum. http://www.monex.com/prods/plat_maple.html

If you want a non-ridiculous answer, however, I'd look a bit farther down the chart.

You might also want to check out the densities for Brass and Bronze, common engineering alloys of copper, to see how they compare to the other densities listed on that chart.

Jason

[s1900ahon]

Originally Posted by patrickggh

..can use for the drive train of a robot in the FTC game...

can use = may use? i.e. it is legal to use
can use = practical to use? i.e. it is dense and strong
can use = theoretically use? i.e. it is really heavy in a small volume

If the last, and you're needing a dense material for increasing weight.. Formula 1 racing teams build super light race cars (well under the minimum weight requirements) and then add a tungsten-nickel-iron alloy (a product called DENSIMET(R)) for ballast. I have no idea how much it costs, but given F1 budgets, it can't be cheap (likely failing the first and second meanings of "can use").

[JesseK]

Lead is sometimes used in FRC as ballast (2009). Just don't eat it and you're fine.

Keep in mind that you *can* have a ridiculously heavy robot. Yet after a certain point, it's not worth it -- the FTC motors are very inefficient and the batteries do not charge very quickly.

[Nemo]

I see no reason to use anything other than steel as ballast. 3.5 cubic inches of steel is a pound, and steel is the cheapest relatively dense metal. If you want a really heavy robot, build a ridiculously over-designed steel frame out of solid bars.

[Gary Dillard]

I use Andy Baker to build my drive trains. He's pretty dense

[Richard Wallace]

Originally Posted by Gary Dillard

I use Andy Baker to build my drive trains. He's pretty dense

Andy is faster than a speeding bullet, more powerful than a locomotive, able to leap tall buildings at a single bound -- look, up in the sky ....

Back to FTC ballast -- I recommend U.S. Pennies. You get 100 for only a dollar. They are 0.75 inch in diameter, 0.061 inch thick, and made almost entirely of zinc. A stack of 182 is just over 11 inches long and weighs about one pound.

If you have a bigger budget, try U.S. Nickels. They are slightly larger in diameter (0.835 inch) and made mostly of copper, which is denser than zinc. Their larger diameter and density means you only need a 7 inch stack (91 coins, or $4.55 worth) to make one pound of ballast. This is 2.5 times the cost of Penny ballast, at 1.282 times the density.

[Gregor]

Originally Posted by Richard

Andy is faster than a speeding bullet, more powerful than a locomotive, able to leap tall buildings at a single bound -- look, up in the sky ....

Back to FTC ballast -- I recommend U.S. Pennies. You get 100 for only a dollar. They are 0.75 inch in diameter, 0.061 inch thick, and made almost entirely of zinc. A stack of 182 is just over 11 inches long and weighs about one pound.

If you have a bigger budget, try U.S. Nickels. They are slightly larger in diameter (0.835 inch) and made mostly of copper, which is denser than zinc. Their larger diameter and density means you only need a 7 inch stack (91 coins, or $4.55 worth) to make one pound of ballast. This 2.5 times the cost of Penny ballast, at 1.282 times the density.

It's times like this when I wish we could spotlight entire posts

[JesseK]

Originally Posted by Richard

If you have a bigger budget, try U.S. Nickels. They are slightly larger in diameter (0.835 inch) and made mostly of copper, which is denser than zinc. Their larger diameter and density means you only need a 7 inch stack (91 coins, or $4.55 worth) to make one pound of ballast. This is 2.5 times the cost of Penny ballast, at 1.282 times the density.

I just knew that one of these days someone would suggest a feasible way to throw more money at a problem. Mo' money? Problem solved!

[Andy Baker]

Originally Posted by Gary Dillard

I use Andy Baker to build my drive trains. He's pretty dense

My weight is about 225 pounds. My volume is somewhere between 10,000-15,000 cubic inches (rough guess). If we assume the smallest volume of that range and divide 225/10,000 that equals 0.0225 lbs/in^3.

Considering these commonly used robot-construction materials:

• Aluminum = 0.1 lbs/in^3
• Plastic = 0.05 lbs/in^3
• Steel = 0.28 lbs/in^3

... and comparing them to my meager density of 0.0225, then I would strongly suggest not to put me on your robot.

Originally Posted by Richard

Back to FTC ballast -- I recommend U.S. Pennies. You get 100 for only a dollar. They are 0.75 inch in diameter, 0.061 inch thick, and made almost entirely of zinc. A stack of 182 is just over 11 inches long and weighs about one pound.

If you have a bigger budget, try U.S. Nickels. They are slightly larger in diameter (0.835 inch) and made mostly of copper, which is denser than zinc. Their larger diameter and density means you only need a 7 inch stack (91 coins, or $4.55 worth) to make one pound of ballast. This is 2.5 times the cost of Penny ballast, at 1.282 times the density.

Originally Posted by JesseK

I just knew that one of these days someone would suggest a feasible way to throw more money at a problem. Mo' money? Problem solved!

You may as well just pull out the big guns and use a stack of these!

Andy B.

[Gary Dillard]

Originally Posted by Andy Baker

...that equals 0.0225 lbs/in^3.

Which explains why Andy floats. But what also floats? A duck. And wood. So logically, if Andy weighs the same as a duck he must be made of wood, so he must be? ..... A WITCH!!!!!

[Richard Wallace]

Originally Posted by Andy Baker

You may as well just pull out the big guns and use a stack of these!

Uh, Andy ... those little beauties cost $240 each and are smaller than a penny. Each one contains about 1.2 gram of gold, alloyed with a smaller mass (but about equal volume) of something with lower density -- maybe silver, maybe copper or ? Mass of each coin is not specified in the ad, but is probably about 2 gram; i.e., about 80% the mass of a penny.

In cost-effectiveness terms, that's a lot of buck for not much bang.

A more practical alternative, and one that many FTC teams would actually choose, is steel ballast. One example is 0.75" diameter low carbon steel bar stock, McMaster 8920K19, $31.12 for a 6 ft. bar. An eight inch length of this bar stock would give you the same ballast mass as the aforementioned eleven inch stack of pennies, at a pro-rated cost (which assumes you have another use for the rest of the bar) of $3.45. About 1.9 times the cost of the Penny ballast, with 11/8 = 1.375 times the density. Steel is looking good compared to U.S. Nickels, and VERY good compared to gold coins.

But again, in terms of cost-effectiveness, the U.S. Penny is hard to match.

[DonRotolo]

I'm surprised nobody mentioned depleted uranium...

[PAR_WIG1350]

Originally Posted by DonRotolo

I'm surprised nobody mentioned depleted uranium...

Because it's radioactive

[dtengineering]

Originally Posted by Richard

In cost-effectiveness terms, that's a lot of buck for not much bang.

The O.P. asked for the densest FTC legal material, which certainly leaves room for ridiculous answers. That's why I suggested Platinum coins, which should actually be both denser and offer better bang/buck ratio than gold. (Clearly a much less ridiculous answer, no?) :-)

But the roll of pennies got me thinking as to which coin would be best to use from a price/mass ratio. For instance, it would probably be cheaper to use American pennies than Canadian ones because the Canadian dollar is trading higher (this week, at least... a big change from being in the sixty cent range when I started playing this game a decade ago.)

I couldn't find out which nation's coinage offered the best mass per dollar ratio, however the closest information that I could find was this site http://www.coinflation.com/ If you go for a pre-1982 US penny, you are actually getting 2.45 cents of copper in every one of them.

Not a bad deal at all.

Jason