3D Modeling and Feeder Prototype

Our feeder prototype came back from the machine shop this week:

This design was adapted from the artificial feeder specifications detailed by Thomas Seeley in The Wisdom of the Hive.  An inverted glass jar on the top of the feeder will hold sugar water, which will be dispensed to the bees via slits ("feeding troughs") in the glass plate underneath the jar.  The glass assembly sits atop a wire screen nested into a wooden plate, underneath which is a petri dish containing essential oils to entice the bees to the feeder.  The final version of our feeder will include brightly-colored artificial flowers and electronics to track the visits from bees.

As part of the feeder design, we plan to add artificial flowers to visually entice bees to the feeder and provide an enclosed space to contain our infrared photogates, which don't give reliable readings in bright sunlight.  Since we have access to a 3D printer on campus, I'm using 3D modeling software to design the flowers for the feeder.  I first considered two possible shapes of tubular flowers:

The original plan was to cut a slot into the lower half of the flower to hold the photogate, but the assembly of the feeder-electronics system might turn out to be easier if we place the photogate over the top half of the flower.

I started trying to design flowers in both SketchUp 8 (the free version of Google's 3D modeling software SketchUp for Mac OS X 10.6) and SolidWorks 2012.  After spending a few hours experimenting with each piece of software, I decided that SolidWorks would be better suited for this purpose.  There are, however, aspects that I like and dislike about both programs.  Some notable features of each:

SketchUp 8

• more intuitive interface
• easier to learn
• can delete any surface with the delete key (surprisingly nice)
• can specify dimensions of shapes when created
• can draw 2D shapes anywhere on model
• exports to STL (3D printing file format) with a free add-on
• curves are shown as linear approximations
• funny things can happen when trying to build small curved surfaces
• model will always render, so you need to manually check for non-manifold geometry before 3D printing

SolidWorks 2012

• better support for curved surfaces
• support for bilateral and radial symmetry
• can specify dimensions of shapes when created
• dimensions of features in the model can be changed at any time
• natively exports to STL
• model won't build if it contains non-manifold geometry
• complicated menus and rigid, sometimes non-intuitive model structure
• can be difficult to delete components in the model
• can be difficult to find the source of build errors
• all 2D shapes must be created in a separate "sketch" on a planar surface

Despite the time required to learn the rules of SolidWorks (and the frustration of getting them wrong and not knowing why something doesn't work the way you expected), it's clearly the better choice for this application because it handles curved surfaces (and 3D components in general) much better than SketchUp, and it supports resizing components in the model – I will probably need to make adjustments both as I'm building the initial model and after we print the first flowers to test on the feeder assembly.

A hollow dome, with a rim, that I modeled using SketchUp.  After revolving the inner contour of the dome around its circumference, I had to create the outline of the outer wall separately and revolve that as well.  I ended up with a non-manifold shape at the top of the dome.

My initial attempt at creating the first tubular flower model in SketchUp.

The model didn't render the way I expected it to when I dragged the shell around the small bend at the end of the tube.  I tried to close it off, but I wasn't particularly successful.

A preliminary model built in SolidWorks.  (Notice the smooth curved surface!)  I'm planning to remake the petals into a more natural shape and slice off part of the end of the flower so it will fit against the glass jar.  I also need to design a mechanism to keep the flower upright and in place on the glass plate, as well as cut the slit for the photogate.

SolidWorks supports radial symmetry – I created one petal and then iterated it eight times around the circumference of the flower opening.  Incredibly convenient.

Notice how, in the flower model above, I added slits to each of the petals.  These are intended to be nectar guides, which most flowers in nature have to guide pollinators toward their goal.  While nectar guides are usually visible to the human eye – indicated by either patches or stripes of color that contrasts with the rest of the petal – bees are also attracted to ultraviolet nectar guides, which show up as even more distinct color differences than the ones we see.  However, the nectar guides on our artificial flowers will be relatively simple – just indentations in the petals, to which we may add color in order to make them more visible to the bees.