Print Prototype and Evaluate Assembly
Summary
Multiple components of the crossbow were handed off to the TA so that they could be printed on the Stratasys. These included the Main Body, Bow, and the Crank Mechanism. These were the core components of the crossbow and therefore we wanted immediate feedback on how well they would print. Notable exclusions from the items initially printed included the trigger mechanism which is still undergoing redesigns in Solidworks in order to be compatible with the newly printed components.
Main Body
We were very pleased with the structural rigidity of the main body in light of the fact that we removed so much material from the underside. Upon receiving the part, much of the support material remained and needed to be removed before we could properly verify that the accompanying components would slide in place for a good fit. We anticipate that no further redesigns or prints will be required of the body. This is good because we were informed that it took a significant amount of print time and will also take as much as 48 hours in order for all of the support material to dissolve.
Bow
When the bow came back we were surprised by how flexible it was. It was designed with some flexibility in mind, but we have opted to make multiple design changes in order to optimize further prints. Specifically, the center of the bow had visible stress concentrations when the bow was flexed which contributed to less than desirable performance. In addition, we noted that too low of an overall height was chosen for the drawstring attachment points which caused the drawstring to drag across the main body. In order to mitigate this, the center of the bow will be doubled in the middle (0.5″ thickness) and then taper down to 0.25″ thickness on the sides. This should serve to increase the overall inertia of the bow and lead to a higher energy dissipation upon firing. Lastly, the drawstring attachment points will be elevated by 0.25″ in order to eliminate dragging across the body.
Crank Mechanism
The printed crank mechanism had superior structural stability and will require no further modifications or prints. Preliminary, unofficial testing was performed by applying a force between the gears and the ratchet prawl of the main body.
Future Prints
As previously mentioned, we will continue to print more advanced generations of the bow as our testing indicates. In concert to this, a trigger mechanism will be printed next in order to fully test our crank mechanism and steel pins will be purchased in order to hold the assembly.
Note: All printed parts have been resubmitted to the TA in order to have support material dissolved. This has prevented us from carrying out future tests and including pictures in this post.