This a solo design.
Now that you have built the classic Popsicle Bridge, you get to apply your knowledge and skills to a 3d printed version.
You will design, print, and test a small box girder bridge using Tinkercad.
We will test the bridges by hanging weights from your structure.
Background
A box girder is one of the most common bridge forms in real infrastructure. Highway overpasses, rail bridges, and pedestrian bridges around the world use this design.
Your bridge will be built at 1:64 scale — the same scale as a Hot Wheels car. At this scale, 150mm represents a real span of about 31.5 feet, and your interior clearance is sized to allow a semi truck to pass through.
The Bridge
Your bridge consists of exactly four printed parts:
* One deck panel
* One top panel
* Two side panels (left and right)
The top and bottom panels MUST have a minimum 15mm in diameter vertically aligned hole that will allow a hook to pass through both layers. The hook will hold a weight BELOW the bridge.
All four parts are held together with M3 screws and recessed nuts. No glue is permitted.
Required Dimensions
Deck: 46mm wide, 3mm max thickness
Top panel: 46mm wide, 3mm max thickness
Side panels: 71mm tall, 3mm max thickness
All parts: 150mm max length
Center hole: at least 15mm in diameter
Overall height: no more than 75mm
Interior Clearance
Minimum: 40mm wide × 65mm tall
A Hot Wheels semi trailer must be able to pass through your assembled bridge. This will be checked before your bridge is approved for printing.
Panel Design Requirements
None of your panels can be solid without holes. Think about bridge design? A bridge that is fully enclosed by solid surfaces is not a bridge. It’s a tunnel.
Think of your bridge as a supporting skeleton.
Fasteners
We will use the same fasteners that you used for the 3d printed chair and linked shapes.
* 8 M3 screws – make the bolt hole 3mm in diameter.
* 8 M3 nuts
Each attachment must be where a bolt and hex nut connect.
Each hex nut must be recessed into the bridge material with supporting plastic around it.
This gives you 4 connection points.
Think about:
* Where your bridge will bend
* Where parts may try to pull apart
* Where forces are highest
Testing
We will hang the weight from the top panel of the bridge.
The hook will be attached to a hook that will connect to a wood plank that will spread the load across the entire bridge structure.
Awards will be given to:
Overall weight held before collapse
Best bridge weight ration to overall weight capacity (how much the bridge can hold)
Grade will be reduced IF:
The bridge does not meet dimension guidelines.
The bridge fasteners do not fit cleanly and/or align.
What do you turn in? Complete step 1 and step 2.
1. Canvas: a screenshot from Tinkercad of your finished design. How to take a screenshot in Windows.
2. For printing: upload the STL file of your design to this Google Form.
Here’s how to convert files to STL:
-in Tinkercad click the EXPORT button in the top right hand corner. Choose STL as the file format. Pay attention to where the file downloads on your computer. -make sure that the file has your last name (like milsteadcompleteshape.svg). No name=no 3d print.
When you are done click here to submit your design.