Our ME 514 Project is about designing and printing a handheld crossbow. We want to design our crossbow to shoot modified straws.
The idea is based on two different designs provided on Thingiverse.com. We want to combine these designs to make our own crossbow and optimize it for long distance shooting.
Goals and Requirements:
- design a crossbow that shoots a long distance
- adjust the elasticity of the bow by modifying the design, size, and the printing parameters
- capable of withstanding load when drawn back
- requirement for long-term use
- scaling up the current design
The first idea our design is based on is the Snap Fit Mini Crossbow http://www.thingiverse.com/thing:964321
We want to use the trigger mechanism and track of this design and maybe add in a safety mechanism so it doesn’t fire unexpectedly. Furthermore we want to use straws as projectiles since their weight is easy to adjust by filling them with some material or using tape to redistribute the load.
The second idea is the Diminutive Defender http://www.thingiverse.com/thing:708766
We are interested in the flexible and bending bow design of this crossbow version.
That’s why we already printed this crossbow to investigate the spring force of the bow. We started printing without changing the parameters to study the properties of the initial design. When we tried to print the part during the lab time we had problems with the extruder. One reason for that was that the heater turned off and the nozzle became clogged.
We finally printed the crossbow with the WANHAO printer in the lab. The printing parameters were:
Material: ABS
Printing time: 48 minutes
Infill percentage: 20%
Layer height: 0.3 mm
We figured out that the bow is very elastic but not stable and strong enough since it broke after bending a couple of times. We discovered that we have to design a bow that is thicker than the initial Thingiverse design to withstand the forces while bending it.
The critical component of our design is the bow. We want to investigate and optimize the design and printing parameters like layer height and infill percentage as well as thickness and printing direction to achieve high spring forces for long distance shooting.