Mechanical Design

For this week, our team designed and developed a CNC-based machine. The original idea was to build a system capable of automating the inoculation of bacteria on a Petri dish using a pipette. The concept required precise 2D movement, controlled dispensing, and a stable platform capable of positioning the tool accurately over the dish.

However, during the design process we identified an important limitation: mechanical vibration. Because the system was intended to work with a pipette and very small volumes, even slight vibration could affect precision and repeatability. Instead of continuing with a concept that could compromise performance, the project direction changed into a more suitable application for the machine structure.

The final concept became a machine capable of generating light-based images using a NeoPixel ring and a camera. In this new approach, the moving system controls the light source and the camera captures the generated pattern. This made much better use of the machine’s motion platform without being negatively affected by small vibrations in the same way a pipetting process would be.

My contribution focused on the mechanical design. Specifically, I was responsible for designing the corner parts of the structure where the motors and bearings are mounted, as well as the carriage that originally would support the pipette system.

Mechanical design was one of the most important parts of this project because the entire CNC system depends on rigidity, alignment, and controlled movement. Even though the final application changed, the machine still needed a stable frame, properly aligned moving axes, and components capable of supporting motors, bearings, and carriage elements.

The first design intention was centered on biological automation, which required:

• Precise linear movement
• Low vibration
• Stable pipette positioning
• Controlled motion over a Petri dish

When the project shifted toward light painting with a NeoPixel ring and camera capture, the same motion structure remained useful. This meant the mechanical design still had value, especially in:

• Supporting stepper motors
• Guiding movement with bearings
• Holding moving modules
• Maintaining structural stability

This design process demonstrates an important engineering principle: even when a project changes direction, a robust mechanical foundation remains useful if it was designed with modularity and functionality in mind.

All my parts were designed in SolidWorks. I used this software because it allows precise parametric modeling, dimensional control, and easy iteration when parts need to be adjusted to fit shafts, bearings, motors, or printed assemblies.

SolidWorks was especially useful in this project because the parts had to satisfy multiple mechanical requirements at the same time:

• Exact positioning of mounting holes
• Alignment between motor shafts and motion components
• Proper seating for bearings
• Geometric consistency across repeated structural parts

Since these components were part of a larger assembly, designing them parametrically also made it easier to adapt them if the team modified the frame dimensions or changed the motion system.

The parts I designed were focused on the structure and motion support of the machine. Based on the files I created, my work can be grouped into two main categories:

• Corner and structural support components for motors and bearings
• The carriage system that originally would hold the pipette module

These parts were essential because they define how the machine is assembled mechanically, how loads are transmitted through the frame, and how the moving system is guided.

General Role of the Corner Parts

The corner parts are among the most critical mechanical elements in a CNC system because they connect the structure, support the motors, and maintain alignment between moving elements. In a machine like this, the corners are not just connectors: they act as load-bearing geometry that defines the rigidity of the frame.

My corner-related files include:

• Esquinas.SLDPRT
• EsquinasBase.SLDPRT
• EsquinasRodamientos.SLDPRT

Esquinas.SLDPRT

This part appears to be the main corner element of the structure. Its purpose is likely to connect the axes or structural members while also providing a reference geometry for the rest of the assembly.

In a CNC machine, a part like this must be designed carefully because:

• It defines the orthogonality of the frame
• It supports the mounting of additional mechanical elements
• It contributes to the overall rigidity of the system

A poorly designed corner can introduce misalignment, which would later affect motion smoothness, bearing contact, and repeatability.

EsquinasBase.SLDPRT

This part most likely corresponds to the base version of the corner. Its role is probably related to anchoring the machine to the lower frame or creating the first support plane for the vertical and horizontal members.

A base corner part is important because it usually needs to:

• Provide stable support for the machine structure
• Distribute load toward the frame
• Maintain alignment with the rest of the assembly

In practical terms, this means the base part must be dimensionally consistent, flat, and robust enough to prevent deformation during machine operation.

EsquinasRodamientos.SLDPRT

This part was specifically related to the bearing system. Bearings are essential in CNC machines because they reduce friction and guide motion in a controlled way. A corner part designed to hold bearings must be accurate, since any misalignment directly affects movement.

The design intent of this component was likely to:

• Create a precise housing for bearings
• Keep the bearings aligned with shafts or guide rods
• Provide structural support without excessive flexing

This type of part is mechanically sensitive because tolerance matters. If the bearing seat is too loose, the motion system loses precision. If it is too tight, it may generate friction or assembly difficulty.

Another major part of my contribution was the carriage system. Originally, the carriage was intended to hold the pipette used for bacterial deposition. Even though that application was later changed, the carriage still represents an important part of the machine’s mechanical concept.

The carriage is the moving body of the system. Its job is to travel along one axis while carrying the active tool or module. In the first concept, that tool was a pipette. In the modified concept, the same motion logic can be adapted to support the light or camera-related module.

The carriage-related files include:

• Carrito.SLDPRT
• modular.SLDPRT
• Moduloservo.SLDPRT

Carrito.SLDPRT

This was the main carriage body. It was designed as the platform that would move across the machine while carrying the dispensing or actuation mechanism.

A carriage in a CNC-type mechanism must satisfy several requirements:

• Low mass, to reduce inertia
• Sufficient rigidity, to avoid vibration
• Mounting features for additional modules
• Compatibility with guides, bearings, or linear motion elements

Since the original system was intended to manipulate a pipette, stability was especially important. Any vibration or wobble at the carriage level would translate directly into positioning error at the pipette tip.

modular.SLDPRT

This file suggests a modular design approach. The purpose of a modular part is usually to allow the machine to adapt to different payloads or mounted systems without redesigning the entire carriage.

Designing modularity into the carriage was a valuable decision because the project concept changed during development. If the carriage had been designed only for one fixed tool, the system would have been much harder to repurpose. A modular interface gives flexibility and increases the usefulness of the machine.

In engineering terms, modularity improves:

• Adaptability
• Maintenance
• Future upgrades
• Design reuse

Moduloservo.SLDPRT

This part appears to be the servo-related module. In the original pipette concept, a servo could be used to actuate a small movement such as pressing, lifting, dispensing, or positioning the pipette assembly.

Even if the final application changed, the servo module remains important because it represents the interface between linear movement and local actuation. A machine does not only move in X and Y; often it also needs a local mechanism to actuate a tool.

The design of a servo support module typically requires:

• Correct mounting hole spacing
• Servo body clearance
• Horn motion clearance
• Rigid attachment to the carriage

These constraints make servo modules mechanically important, especially when they interact with another functional subsystem.

Throughout the design of these parts, several mechanical principles had to be considered:

• Rigidity: the structure must resist deformation under motor movement and carriage loads.
• Alignment: motor and bearing supports must preserve the geometry of the motion system.
• Tolerance: bearings, screws, shafts, and printed parts must fit correctly.
• Modularity: the machine must remain adaptable even if the final application changes.

One of the most important lessons from this project was that a mechanical design is not only about making parts fit together. It is about anticipating motion, load paths, assembly constraints, and how design changes can affect the behavior of the entire system.

A key part of this week was understanding that engineering design is iterative. The original concept of automating bacterial deposition was promising, but once vibrations and stability issues were considered more seriously, it became clear that the system would not perform with the required precision.

Instead of forcing the original concept, the team adapted the machine into a system that draws with light using a NeoPixel ring and a camera. This was an important design decision because it reused the machine platform while aligning the application with what the mechanical structure could do more reliably.

This change also highlights why modular mechanical design is valuable: when the final use changes, the structure and motion system can still remain relevant if they were designed with flexibility in mind.