The outer shell for Pingbot was designed using Autodesk's FREE
123D 3D modeling software. It took me about a week of fiddling around with the program and referencing the tutorials
before I got the feel for it. Once I had a handle on the basics, I chose a material and created the final model. The model was saved as an STL file, a common 3D model file type, and uploaded to 123D for fabrication. The completed model along with a version containing the separated
components are both available in the 123D gallery
, where they can be viewed in an interactive 3D preview. They are also included with this Instructable.
Choosing a Material
It is important to choose a material before
you start working on a model as each material has different guidelines that you must follow while you are designing. The materials vary in the minimum wall thickness, minimum detail size, flexibility, and other properties. Some materials are weaker than others, large models made from them may need inner structure to support the weight.
I chose to have the shell for the Pingbot printed from the Durable Fine Plastic
. This material is strong enough to be used as a working prototype and its minimum detail is a minute .2 mm.
It is more costly than other materials, but since the cost of a model is partially determined by its volume, the shell was incredibly inexpensive to have fabricated. All totaled, it uses less than 1/3 cubic centimeter of material.
Creating the 3D Model
Although it was printed as one solid piece, the 3d model was made from separate components that come together to make a hemisphere. This was necessary as it allowed the edges of each of the parts to be rounded off.
To begin I created a hollow hemisphere with a 1mm wall thickness. I then copied/pasted the original shell, drew new shapes, and extruded these new shapes to subtract (and intersect) from the hemisphere. After completing all the parts I beveled the edges to create the seams. I've included a couple of pictures of the process.
While designing this robot's shell it was important to remember to add holes for the components that needed to be accessed from the outside. For the USB connector and micro-switch I use the PCB design along with the components' data sheets to determine where, and how big, the access holes needed to be. I also added some holes in the back to help let out the sound from the peizo speaker (the speaker was plenty loud and these holes were likely not necessary).
Upload and Fabrication
In order for a model to be printed, all the separate components need to be welded together to create one solid piece. Once this is done It can be saved as a STL file and uploaded for printing and sharing. (You will need to be logged into 123D to be able to save as an STL.)
This video is of the Object Connex 3D fabrication machine, which is likely close enough to the model of machine used to create the Pingbot shell. It demonstrates how the machine prints the model in layers along with a support material. When fabrication is complete the support material is blasted away leaving the final piece.