Friday, May 25, 2007

a couple more outtakes and simulation update

The simulation of Movement 114 is 30% complete after 52 hours. And in the spirit of the last post here are a couple other things that are not exactly frame worthy. The first is rather technical. If that's not your thing, scroll past it for something very embarrassing.

First an honest attempt at measuring the modulus of rigidity of a carbon nanotube. I had intended to post this to see if anyone knows why it went so horribly wrong.

I used this equation for the modulus of rigidity: G = (TL)/(Jθ)

Here T is torque = 500e-9 N-m
L is length of the tube = 24.51e-10 m
J is the polar moment of inertia. Here I used (π /32)[(d1-d2)^4]. d1-d2 would be the thickness of the tube. For this I looked up the covalent radius of carbon (77pm) and multiplied it by two to get the diameter of the carbon atom and subsequently the thickness of the tube.
θ is the amount of twist the torque accomplished. I used a jig to measure this and it came out to 12.3 degrees or 0.21 radians.

When you do this arithmetic you get a ridiculous answer, something like a billion-trillion Gpa.
Anybody see anything I didn't?

And before I decided to totally redesign Movement 114, in a moment of desperation, I was actually considering something like this:

Yes those are carbon nanotube halves bonded to the rack. I sure hope the new design works...


Loki said...

I'm a bit confused by some of your rack and pinion designs. They have the circular gear engage both the upper rack and the lower rack. Won't that cause the upper rack to be pushed left and the lower rack to be pushed right, causing no overall movement?

Tom said...


It shouldn't because the pinion only has teeth on a third of its circumference, so when the teeth are engaged on the top of the rack, the bottom is disengaged from the pinion and vis versa.

The May 20th post shows this a little bit, but I admit it is pretty hard to tell. It is more apparent in the design console where I can rotate the pinion and (hopefully) line it up enough to only engage one side of the rack at a time.

Thanks for the question though.