Testing and Design Optimization
To test the initial design of the Snap Fit Mini Crossbow we printed the grip and trigger mechanism with the Flash Forge Replicator Dual. We investigated if the assembly of the grip and the trigger mechanism works properly.
Printing parameters:
Material: ABS
Infill percentage: 30%
Layer height: 0.2 mm
Building time: 2 hours 10 minutes
The pictures below show the single parts of the grip and the assembled grip with the trigger. There were some problems with the assembly of the trigger since the plug-connection does not fit together well due to remaining support structure at the pin of the trigger. Furthermore the grip cap was hard to assemble due to the tolerances the printer was able to print. It does not fit well and the cap was hard to attach to the grip body.
There are different optimization ideas to solve this problem and ensure a proper assembly: The first idea is to use a printer with a higher resolution. A printer where we could print a layer height of 0.01 mm instead of 0.2 mm could print the details like the pins more accurate and achieve better tolerances for a smooth assembly of all parts. The second idea is to scale the grip up to double its actual size to achieve a better resolution of the printed details and the pins. Another reason and advantage of the increase in size is that the handling of the small grip is not very comfortable at its original size since it is too small.
Part Strength and Bow Design Optimization
In the prior blog post we said that we want to eliminate the need of an elastic rubber band by designing the arch of the bow to be elastic so it can provide power for shooting an arrow and also return to normal when the string is released. Since the print of the first black Diminutive Defender bow design showed that the elastic bow part breaks after using it a couple of times we figured out that the bow made of plastic (ABS) could not really be elastic. If the bow part is elastic, it would be too week to resist the forces and will break, thus it is not able to store the energy. That’s why we designed the new bow which is thicker and stronger. We want to use a rubber band to draw the bow. The main forces for shooting a straw should come from the rubber band and only a small part should arise from the elasticity of the printed bow to guarantee a durable functionality.