Manufacturing Challenges

We utilized laser cutting for manufacturing our prototype due to the time limitations of this project. Laser cutting allows us to quickly and cheaply manufacture several parts from CAD files. We therefore designed all our parts to be planar, so that we could export their two-dimensional drawings as PDFs to Retina Engrave, where we could vector cut the parts.

Vector drawing of planar parts to be exported to Retina Engrave

The biggest challenge with laser cutting was to determine the exact tolerances for tight fit parts. Laser cut parts usually end up having a smaller perimeter and larger slots/holes than the CAD models due to burn of the material in the process. Furthermore, the automatic z-offset of the laser cutter was malfunctioning, requiring us to do several passes of laser cutting until the parts separated from the wooden sheet. In order to get the correct tolerances, we laser cut a series of parts in a grid and chose whichever one worked best for the tight fit assembly.

Dimensioning grid for determining size of slots

The first prototype, which comprised of only one planar wing, was entirely cut out of ⅛ inch wooden sheets. The joints were made using steel bearings that were tight fit into the wooden linkages, connected by ⅛ inch drive shafts, and capped off with retaining rings.

The wing mechanism for the second prototype was also manufactured using the ⅛ inch wooden sheet. However, we also needed to manufacture a cage for suspending the main wing mechanism from. We needed to suspend the standard servo motor for the rocker, and also hinge the joint (connecting link 1 and 4) from the cage, and all these points had to be co-linear. We chose to use acrylic ⅛ inch sheet so that we could see through the cage and focus more on the main bird mechanism.

 CAD model showing cage supported by struts attached to base

Building the cage was quite a challenging task. We needed a secure structure that would not vibrate or shake as the rocker swung the entire mechanism back and forth. Therefore we had to add reinforcement to the structure in the form of struts connecting the arches to the base. The suspension points for the hinge joint also had to be shifted back and forth on the side arches till the mechanism worked properly, as we had to ensure that those joints and the servo were co-linear. Even though in the original CAD assembly, all slots were designed to ensure the correct geometry, offsets were included in the physical prototype during assembly. Similarly, we had to laser cut several different sized links for the connecting bar housing the servos for wings, to make sure that the dimensions were correct and fulfilling the Grashhoff condition.