If you were to build a nanotube model for vibration modeling purposes

[Howard]

With springs as the carbon-carbon bonds and "something" to connect the springs together as the carbon atoms do, how would you build it?

I'm looking at using machined springs to connect the "atoms" together, but I'm not quite sure how to attach the springs together. Machined springs may be designed with stud/tapped ends, hook ends, plain ends... pretty much any type of connector that can be machined conventionally.

Each "atom" will need to fix 3 springs together.

EDIT: Perhaps I can order a great many spheres, cast with the 3 required holes in situ. Then I can order machined springs with pin ends and epoxy them in place. Ideas?

 

[CycloWizard]

There are a few ways it could be done, but it seems like a simple weld would be the easiest. The balls were my second idea, but if you're having things machined, I assume they're probably steel, so again welding would be the best way to hold them together. If you don't know how or have the tools to weld (which would be the case for me too ), then epoxy will probably work, as long as you're not putting large stresses on the bonds.

 

[Howard]

You'd need a jig for welding, eh...

I was actually thinking of having the spheres cast in aluminum. The machined springs would be whatever material is cheapest (mild steel or aluminum, I'm guessing).

I don't believe the forces will be too great. The model will be secured to a vibrating platform to find modes and such.

EDIT: Welding is out of the question. We're talking about over a hundred parts.

 

[Howard]

Got myself a fancy new pen holder:

IMG_0873-1.jpg

 

[bobsmith1492]

Haha, nice! Did you build that or buy it??

 

[Howard]

Built by a team led by yours truly.

EDIT: Didn't think HT was so popular.

 

[Born2bwire]

Man, I would have just used toothpicks and balls of styrofoam.

 

[Howard]

Originally posted by: Born2bwire
Man, I would have just used toothpicks and balls of styrofoam.

Yeah, but you wouldn't vibrate something like that, would you?

 

[Born2bwire]

Originally posted by: Howard

Originally posted by: Born2bwire
Man, I would have just used toothpicks and balls of styrofoam.

Yeah, but you wouldn't vibrate something like that, would you?

Well you could make it vibrate, as long as you're ok with it being able to do it once and run the risk of losing an eye.

 

[videogames101]

How did you end up attaching those springs?

 

[Paperdoc]

Forty years ago students of organic chemistry used to buy model kits to build molecular models much like you describe. The kit had lots of wooden spheres about 15 mm diameter, each painted a color to represent one type of atom. Each had small holes drilled into it, depending on which atom it was. Black balls had 4 holes placed along the axes of a tetrahedron to represent carbon. Hydrogens were white balls with one hole, Oxygen was red with two holes, Sulphur similar but was yellow, halogens were green with one hole, Nitrogen was blue with three holes again arranged like tetrahedral axes, etc. Then came the springs. They were steel springs about 25 mm long, about 2 mm diameter, with slightly tapered ends. To assemble you simply twisted the end of a spring into a hole - they were sized so the spring tightly screwed into the wood. Unscrewing took them apart. Some springs were a little longer and you could use two of them (bent into arcs) to join two atoms with adjacent holes to model a double bond, or three for a triple. Of course, the screwing together operation did not work quite right for the second spring, but just a tight push in would do it.

With this kit you could build whole molecules that were shaped properly, although the proportions of atomic diameters and bond lengths were not exactly right. The springs allowed bending and stretching motions to simulate molecular vibration modes, although sometimes the springs would detach when stressed, suggesting many molecules are fragile!

If you want a more robust version of that system, you could use metal balls and drill threaded holes in them, then make your springs with threaded metal caps on each end. What would be even better, though (thinking of the double bond situation) would be to use small ends and sockets that fasten together with a simple ¼ turn or less. If you wanted to be precise, you could make the balls of different diameters proportional to real atomic radii, and springs of different lengths to allow modeling interatomic distances correctly. I will warn you about an important factor, though. Although such a system will allow you to simulate the DIRECTIONS of vibrations (linear stretching, transverse bending, etc.) they will not model well the relative FREQUENCIES or AMPLITUDES of the vibrations. These aspects depend (in this mechanical model) on the spring force constants (or stiffness) in each direction, which depends on details like the type and size of wires used to make the springs.