## The Basics

What is a Gear Train?

Before we can define a gear train, we need to know what a individual gear is and what it does for a mechanical system. A gear is a spinning wheel with teeth that can “connected” with other toothed devices in order to transmit power and are widely used in many different mechanical devices [1]. In a gear train, two or more gears are used together to transmit power from shaft to shaft that each gear is connected to and there are many different types of gear trains that can be used depending on the mechanical system it will be used in. By using a gear train, the end goal is to increase or decrease the speed or torque of the final shaft in the sequence, which determines the final power output, and you can use something called the Gear Ratio in order to calculate those values [2].

The formula to calculate the Gear Ratio is the number of output teeth divided by the number of input teeth, and you do this step for each gear as you move from one to the other if you have more than two gears.

Gear Ratio Calculation (A-B)

The Gear Ratio is important when calculating a gear’s speed and torque. To calculate a following gear’s speed (rpm), you use your known input gear’s speed and divide by your gear ratio.

Speed Calculation (Gear B)

And finally, to calculate the next gear’s torque, you multiply the input gear’s torque by the gear ratio to find the output gear’s torque.

Torque Calculation (Gear B)

So as we can see through this example with gears A and B, gear B rotates slower and has a higher torque in comparison to gear A.

In order to find the speed and torque of sequential gears past just a gear train with two, you would repeat these steps, however using values found from gear B to calculate gear C, as shown below [3].

Animation going through the steps of adding an extra gear to the gear train

Why do we need one? What is its importance?

A well-designed gear train transmission allows the system to modify the input load into an output that meets the design requirement.

## Design Decisions

For this project, using the harvested motion from waves to spin a generator efficiently to produce meaningful output is the goal, suggesting high angular velocity to be crucial for the generator, allowing its coils to slice through the magnetic field faster to produce more power. As a result, a transmission that has an overall ratio of <1 is needed to speed up the input rotation.

While developing the first complete prototype for our project, we selected a 1:9 overall ratio, which is distributed into two pairs of gears with 1:3 ratios. These design choices were limited by multiple factors:

• Torque limit for the magnetic coupling – an even smaller gear ratio means an even higher torque for the magnetic coupling to overcome, and may cause the coupling to disengage
• Overall size of the system – a direct 1:9 ratio means the driving gear needs to have a pitch diameter 9 times the driven gear, making the component larger than the team desired
• Ease to design and manufacture – the identical 1:3 gear ratio allows same diameters to be used for multiple gears, cutting design and manufacture time

Most CAD software, including SolidWorks, has built in libraries for complex components like gears. The following video shows how to use the SolidWorks toolbox to design your gear train:

If you are purchasing your gears, you can also check out websites like McMaster Carr for selection once you decide on the gear ratio.

A more advanced option is to design your own gear. Keep in mind that designing gears from scratch involves much more than knowing the needed gear ratio. Check out the following link for a more in-depth tutorial on how to make gears on SolidWorks:

## Future Experiments/Design Work

It is important to recognize that this transmission design is not final. Further design iteration can be implemented to fine tune the ratio and dimensions for future improvements.

If you are really interested in transmission design, we recommend you the following textbook:

Shigley’s Mechanical Engineering Design (11th Edition) by Richard Budynas and Keith Nisbett

Here you can find extremely detailed information regarding transmission design and beyond.

## References

[1] byjusexamprep.com. “Gear Train: Types, Formula, Examples, and More.” BYJU’s Exam Prep, https://byjusexamprep.com/gate-me/gear-train#:~:text=A%20gear%20train%20is%20a%20mechanical%20system%20made%20up%20of,Simple%20gear%20train

[2] smlease.com. “Gear Train – Gear Ratio, Torque and Speed Calculation.” SMLease, https://www.smlease.com/entries/mechanism/gear-train-gear-ratio-torque-and-speed-calculation/#:~:text=According%20to%20the%20law%20of,torque%20with%20the%20gear%20ratio

[3] The Engineering Mindset. “Gear Train Animation | Types of Gear Trains Explained.” Online video clip, YouTube, Aug 24, 2021, https://www.youtube.com/watch?v=aGHrhm-Rcp0

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