Sanibel shell curiousity

While walking along one of the beaches on Sanibel Island, Florida, I found a Lightening Whelk shell in shallow water which appeared to have at least two other animals tightly wrapped around it. The whelk did not appear to be alive, but the other animals did, so I decided to take some iPhone photos and return it to the waters where I found it.  Initially I thought the bright orange fibrous strands were something tangled, but then observed that they were tightly anchored and part of these animals.  The photos show the strands coming from the spots on the animals.  I am curious what these animals are, and if they are eating the shell itself, or are using it for some other purpose.

As an aside, this poses a sort of chicken & egg problem:  Because I am not particularly familiar with sea-life, I do not have the appropriate keywords or phrases to find answers to my questions using current language based search technology.  It is intriguing to envision image based search technology that would allow finding pictures of similar creatures and thus information about them!

After a note to the folks at The Bailey-Matthews Shell Museum on Sanibel, I received the following helpful response:

The two animals wrapped around that lightning whelk shell are sea anemones. The orange strands are defensive threads produced by the sea anemone. The single shell attached to the whelk seems to be a common slipper shell.

So, now I have the answer and a pointer toward further inquiry. That the threads are a defensive mechanism probably explains the slight stinging sensation that I’ve had in my fingers…don’t go tugging on something you don’t know anything about!

Life after SketchUp?

A few years ago I found Google SketchUp when I was looking for some cheap CAD software to design a shop building.  After a little bit of playing I was amazed at what could be done with this tool & even more so given that Google made it available as a free download.  I saw that there was SketchUp Pro, but it didn’t seem necessary for what I wanted to do.  At the time I was using both Windows and OS X machines, so the fact that SketchUp was available for both was an important bonus.  I have since left the Windows world entirely and Google has sold SketchUp to Trimble.

With time and use I began to see why there was a Pro version available.  I had a credible 3-D model of my shop, but I also needed to provide my builder with 2-D construction drawings.  I could make do with a section plane slicing off the walls just above floor level, but this felt like a bit of a hack.  Placing the dimensions in the model made sense initially, but was cumbersome working with the model over time.  LayOut (which seems to be the main reason to get the Pro version) is the companion tool to produce construction drawings & is capable of solving the problem elegantly by linking the 2-D and 3-D representations.  Nonetheless, I persisted with the free version and created the 2-D drawings; since my building was fairly straight forward, they served the purpose nicely.

A couple of the things that I really love about SketchUp are its simple interface and inference engine which make model construction a fairly intuitive process.  I also found the tape measure tool which allows quick measurements of the model’s elements to be extremely handy.  While I have some training in mechanical drawing, it dates back to the era of the drafting board.  In the current era, being able to create models with actual dimensions rather than constantly doing scale conversions is an enormous time saver, to say nothing of the corresponding reduction in errors. After using SketchUp for a while I was totally sold on using modeling software for sketching and making “blueprints”…time to consider the Pro version to get LayOut!

Modeling a building sized object was my introduction to SketchUp, but I also wanted to use it for smaller objects with higher precision dimensions.  An example is a chunk of aluminum 6x4x1 inches with features (arcs and holes) drawn to standard shop precision (.001).  A task like this begins to quickly expose design limitations in SketchUp.  First the issue of size and precision.  While SketchUp appears to be able to handle .001 or .0001 precision, some research yielded a post by one of the primary SketchUp developers explaining that SketchUp and LayOut do not work properly at these precisions.  Both tools are apparently targeted more toward the architect and furniture maker rather than the machinist.  The second significant issue for me was how SketchUp handles curves.  At its heart SketchUp is a polygon modeler, so curves are represented as polygons along with everything else.  Normally this isn’t much of a problem, but it can become troublesome when one is designing something via sketching it out and expecting to make accurate measurements.  For example, if I have a circle, then slice off a portion, and now want to measure the corresponding chord length…well, all I get is a rough approximation.  This makes accurate measurements and dimensioning either very difficult or impossible.

SketchUp and LayOut are excellent tools for their intended purpose, unfortunately with experience I discovered that my needs were different.  The moral of the story is to have a clear understanding of goals prior to selecting tools (doh!)–I had leapt at the chance for “free” and had not thought clearly about what I really needed.  After my initial trial of SketchUp, I was hoping to find that it was a generalized 3-D modeling tool that did everything, for free.  Well that is a fairly unreasonable hope, particularly in light of what the professional CAD packages cost.  That cost difference makes SketchUp all the more impressive.

After this experience and having refined my goals, the two packages on my short list to evaluate are FormZ and Rhino.  Having spent a few hours working with Rhino, I really miss SketchUp’s sparse simplicity, but equally I can see the benefit of a far more comprehensive tool when it comes to modeling and producing shop drawings for parts.

Temperature monitoring

36 hour temperature data14 day temperature data

I like to monitor the temperatures in my shop and I receive the occasional question about how I gather these measurements. Well, in stark contrast to expensive commercial monitoring systems, using commonly available parts one can construct a reliable building monitoring system for the cost of an old PC and about $150 worth of sensors. Here is an overview of the components used to build this system.

Sensors are from iButtonLink and are based upon the 1-Wire network which uses simple twisted pair wiring to connect sensors in a variety of topologies. I used an old Amphenol 6 port RJ45 harmonica and wired the ports into a passive hub configuration to create a star topology. The PC connects to the iButtonLink LinkUSB USB master which is in turn plugged into the hub, as are the sensors. All sensors are iButtonLink T-Probes except for the iButtonLink MS-TH which provides both temperature and humidity readings. Note that the DS2438 temperature sensor used in the MS-TH is not as accurate as the DS18B20 used in the T-Probes—a minor nit.

The PC runs Linux (I like CentOS) with OWFS 1-Wire software to read from the sensor network and RRDtool recording/graphing software. A simple shell script called from cron on 5 minute intervals provides for regular data collection.

Have fun!