Parallel Gearbox

Attributes linked to this design project (CEAB's Graduate Attributes):

> Knowledge base for engineering

> Problem analysis

> Design

> Use of engineering tools

> (Individual and) Teamwork

> Communication skills

INTRODUCTION

We were tasked to make an efficient gearbox, and so we designed a parallel system with a 12:1 speed ratio, employing four carefully chosen spur gears. Balancing considerations for speed reduction and 3D printing constraints, we navigated trade-offs, strengths, and weaknesses in our design. Our collaborative effort resulted in successful 3D modelling and testing, showcasing the viability of our gearbox.

PRIMARY DESIGN CHOICES 

The gearbox designed was a parallel gear-box, with a speed ratio of 12:1. The design uses three shafts and four gears to obtain a gear-speed ratio of 12:1. With the input shaft connecting one gear which turns another gear, which is connected to the power transmission shaft which is connected to another gear which moves the gear that is connected to the output shaft to facilitate the transmission of energy. Primarily, the goal of the design is to design a gearbox that would transform rotational energy in a 12:1 ratio to the desired side of the object. The design is supported by moulds that hold the shafts when an increased load is applied. 

Additionally, the design aids in aligning and structuring the gears, preventing deformation when subjected to a load. This is crucial as the material's inherent weakness could lead to misalignment of shafts. The hexagonal portions on the shafts facilitate smooth movement of the gears, minimizing slip without the need for additional connecting mechanisms like screws or glue. Circular portions on the shafts enable unrestricted rotation within supporting moulds. The choice of spur gears, known for reliability and the ability to maintain a constant speed, allows for flexibility in creating the desired gear speed ratio with different sizes and tooth configurations. Given the 3D printing process, the design acknowledges constraints related to size, strength, and build quality, ensuring that the components adhere to the physical limitations of the 3D printer for a functional end product.

PARTS SELECTION 

Four spur gears with 10, 12, 36 and 40 teeth were used in the design, and considerations were made to keep the design within the size and print limitations. While compromising on the strength such that it stays at a sufficient level. The gears have a ratio of 12:1 that meets the design criteria needed. The rest of the parts were made in consideration that they could be stacked and assembled, with three shafts and moulds to support the gears, made in a way that it would only fit if placed in the correct way. 

TRADE-OFFS 

The parallel gearbox which provides a 12:1 speed ratio uses four spur gears. This design approach addresses speed reduction requirements but comes with some trade-offs. Although spur gears are reliable and effective when it comes to maintaining constant speeds, due to their limitations in their load distribution and strength capabilities, it does not handle higher loads as well when compared to helical gears. 

Also, the design’s adherence to size and print limitations allows for easier assembly, it forces a compromise in the strength of the gears and the housing/overall structure. And it impacts the gearbox’s strength and load capacities. Additionally, the use of a parallel gearbox comes with trade-offs when compared to a right-angle gearbox. The primary one is the directional alignment of the torque transmission. The parallel gearbox transmits power along the same plane, whereas a right-angle gearbox may use bevel gears which allows for a change in the direction of the drive by 90 degrees. Also, the bevel gears often seen utilized in right-angle gearboxes are more capable of handling angular loads and larger torque applications in comparison to spur gears. 

STRENGTHS AND WEAKNESSES 

The strength of this gearbox design lies in its incorporation of spur gears, ensuring efficient energy transmission, reliability, and simplicity. Spur gears excel in delivering power consistently and maintaining torque under standard operating conditions. The gearbox features three shafts – input, power transmission, and output – enabling a seamless transfer of energy. Hexagonal portions on the shafts enhance rotation and gear engagement. Molds are employed for shaft support, ensuring better gear alignment, minimizing deformation under load, and extending the gearbox's lifespan. The parallel gear arrangement minimizes energy loss by facilitating linear energy transfer. The modular design allows for easy stacking and assembly, simplifying repairs or part replacements. Individual printing of components ensures straightforward adjustments, as only the specific part requiring replacement needs to be altered.

However, this design is not without its flaws. Although the use of spur gears can be quite beneficial as mentioned above. In certain applications, it may prove to be inadequate. Due to their inability to effectively distribute forces across their teeth, failure or gear deformation could occur in situations where the gearbox must handle high loads. While the moulds provide support for the shaft and allow for better gear alignment, they introduce additional points where failure could occur. 

The team worked together to 3-D model different components of the project, and in the end, succeded when all the tests conducted during the last practical session on the final assembly passed without any damage to the final 3-D printed model.