Skelebot Manufacturing & Assembly

The mechanism is composed of 3 major sections, the skull, the shaft assemblies, and the base. 

Base

The base was constructed out of a hollow rectangular prism of 0.125” thick wooden sheets and houses the primary electronics involved in the mechanism operation. At the top of the base are the mounting points for the two shaft flanges, as well as the primary drive motor mount and the auger outer piping flange. Affixed to the coupling at the base of the auger outer piping flange is a reservoir used for the inlet of candy into the dispensing shaft. 

Shaft Assembly

The shaft assembly consists of one rotating 0.1875” stainless steel rod and one fixed 0.375” stainless steel rod. The fixed shaft runs from a flange mounted to the wooden base and runs up to 2 bearings sandwiched on either side of the lower section of the skull to provide a fixed pivot point and weight support. The rotating shaft runs from the primary drive motor up to the crank-rocker system for skull rotation. Surrounding the rotating shaft is a Ø 1.5” auger within a section of 1.5” PVC pipe (actual ID - 1.61”). At the top of the outer piping section is a “keyhole” rotating door that ensures proper timing of candy disbursement. The top of the two shafts meet at the base link of the crank-rocker subassembly used to drive the movement of the skull body.

Skull

The skull is the primary visual element of the greater mechanism assembly and is composed of 3 3D-printed subsections. The top dome of the skull is removable such that access to the internal components of the mechanism are easily accessible, diagnosable, and repairable. The middle “face” section of the skull is broken into 3 components for manufacturing speed and provides mounting points for the crank-rocker, jaw motor, jaw motor driver, LEDs, and candy dispensing tube. Affixed to the “face” section is a small stepper motor that moves the pivoting jaw during the talking and dispensing stages of the mechanism operation.

Material Breakdown  

Skelebot is composed of parts of multiple different materials and manufacturing processes. The following table breaks down the source of the major components (manufactured or purchased) and shows the primary materials used in the manufacturing process. Note that smaller attachment hardware and electronics are not included in this table.

Assembly

Skelebot was integrated using materials and hardware that were available onsite in the Texas Inventionworks. Some of the hardware, while adequate for the current prototype model, presented issues that could be resolved with design refinement and manufacturing adjustment. There were a number of cases during assembly where certain parts presented issues that forced on-the-fly design changes in order to meet the project deadlines. In some cases, remanufacturing or reordering of parts would have proved too costly or too time-consuming to undertake, and as such necessitated adjustments and workarounds to be used in the assembly process.

One such example is the bearings on the fixed 0.375" shaft, which were listed as a smaller outer diameter on the original spec sheets from the Amazon supplier. This diameter was what the receptacle on the skull was designed for, and when the bearings were delivered were found to be a different size than what was already integrated and manufactured on the base of the skull. Reprinting the lower section of the skull with the amended size was an option, however it would've proven materically wasteful and too time consuming. As such, an adapter was rapidly designed and printed that fixed the size discrepancy for the prototype. Further iterations of the model would not call for such adapters, but with the presented time constraints, many such small fixes and adjustments in manufacturing were required.

Another example of manufacturing difficulties stemmed from issues presented in some of the 3D prints. Since many different individual printers were utilized in the manufacturing process, the tolerance consistence was relatively low and presented issues during assembly. In some prints the tolerance provided too much mechanism play, while in other prints there was not enough room to assemble. This discrepancy presented itself in multiple sections of Skelebot and required quick workarounds and prototyping in order to remedy. Higher quality prints, such as those from the Raise3D printers, were much more accurate in their dimensions, but were more difficult to secure compared to the plentiful, but less accurate Craftbot+ printers.