20 October 2014
I would not be satisfied making trinkets with a 3D printer for my Blue Rabbit Project. There were several false starts while trying to decide what to make, but when I hit on the idea of making something that is functional and that might also work as a teaching aid, I knew I was on the right track. Because I have a background in navigation, it seemed logical to go in that direction. To choose which device to make was a matter of eliminating the impossible ones and then see what’s left.
The first to go were the electronic devices. GPS receivers are small and superbly accurate but far to complex for 3D printing. I could probably make a cover for my GPS unit, but that doesn’t seem like a proper challenge, nor does it provide a teaching opportunity.
Before there was electronic navigation, there was celestial navigation. Tools were used to measure the angular distance of celestial bodies above the horizon. That measurement, along with accurate time and either tabular data or formulas, allowed navigators to determine their position. Foremost among these tools is the sextant. Traditionally made of metal, there are some sextants available in plastic. While we may be getting closer, sextants are still too complex for 3D printing. They have many moving parts plus gears plus optics.
The first device I actually tried to make was an astrolabe. This device is a precursor to the sextant and has far fewer parts. My design has only two parts, a base and a sighting ring. One of the issues I have with this unit is how to read the numbers it generates and another issue is sizing the two pieces so that they don’t bind on the one hand, and they don’t lose too much accuracy on the other. At this point the astrolabe is on hold while I work on the next design, but I fully expect to return to it.
It should be noted that every time we step backward on the technology scale, we lose some accuracy, but if we have to give up accuracy in order to get a tool that works, so be it. That is the deal I am making by creating a plumb bob sextant. This is the simplest design yet and I can guarantee that it will work but I won’t have any idea about its accuracy until it is tested. This device is simply a 3D printed plane with angular values marked at 10-degree increments. A weighted string is attached so that when the upper edge of the tool is angled above horizontal, the angular value of the rotation can be read where the string intersects the scale. (Burch, 149.).
Assuming we can use these tools to measure how high in the sky the sun is (as an example), what can we hope to learn? The sun appears to rise in the sky throughout the morning, stops at its highest point for just an instant, and then begins its descent. The point where the sun appears to stop is very special to a navigator, that is the point when the sun is exactly on the same meridian of longitude as the observer. At that point, latitude can be calculated with just a little addition and subtraction. (Bowditch. 344.) The practical aspect of using these tools is being able to tell where you are. The slightly less practical but equally important aspect is that by looking closely enough at the world around us, we can understand how it works.
Of course, not every seafaring culture has a use for the tools that are so familiar to me. Hundreds of years before Europeans found their way to the Pacific Ocean, Micronesian navigators explored the entire Pacific basin. “Micronesian navigation, I realized, is also an integrated system; instead of being based on charts and instruments, it relies on a vast body of lore and the navigators own senses”. (Thomas. 75.) The test of the Polynesian navigators was their ability to find low-lying islands that are far away. Fortunately for me, my challenge won’t be that difficult.
The tools that I am building will measure angles, and they’ll work fine on targets other than the sun, moon, and stars. I propose that a fair test of the design and execution of my tools (and my math), will be to use them to determine the height of the clock tower on campus.
Bowditch, Nathaniel. The Marine Sextant: Selected from American Practical Navigator. New York: D. McKay, 1976. Print.
Burch, David. Emergency Navigation. Camden, Me.: International Marine Pub., 1986. Print.
Thomas, Stephen D. The Last Navigator. New York: H. Holt, 1987. Print.