The Differential Gear System
By: Mert Culcu, Isabella Soto , Ayaan Riaz
The Inspo
When looking for design online for inspiration, our group quickly became very intrigued by the gear system of differential. A car’s differential is what allows for a car’s wheels to spin at different speeds when turning. Car differentials use bevel gears, so we knew this was going to be a challenge to model with laser printed gears.
Initial Sketch Files!
In this sketch we have the model of a car differential. The purpose of this differential is to distribute power to the two wheels equally, while still allowing them to turn at different speeds, or not turn at all. The way this model works is a user would crank the lever connected to gear 1 causing gear 1 to interact with gear 2. Gear 2 would then spin moving gears 3 and 4. Gears 3 and 4 would then cause the movement in gears 5 and 6. Since gears 5 and 6 are not directly attached, their movements would be independent of each other, such that stopping gear 5 would not stop the turning of gear 6.
Our Low Fidelity Prototype!
The image to the right is the file we first printed on cardboard to see how this model would act/assemble in real life. We began with printing this design on cardboard. Cardboard isn’t a strong material but was very helpful to catch errors and ideas on what other factors to consider.
To the left are the cut outs of gears and structure we laser printed on the cardboard. During the assembly process, we used a glue gun that attached the individual elements of the structure together. We found dowels that can fit to the holes on the gears and cut them to use them more efficiently. Once we finished the assembly, we tried to test if the mechanism works, however we ran into issues like the fragile nature of the cardboard caused it to become damaged when the gears were rotated. Also the overall size of the whole mechanism was a bit small, so we decided to increase it by some scale.
Our Medium Fidelity Prototype! (no bearings – no problem)
During our medium fidelity prototype stage, we have decided to implement a car theme since we are doing a differential. For this reason, instead of using rectangular pieces for the structure we came up with a box design which not only helped to better implement the overall car concept, but also provided a more stable and structured way to hold the dowels in place.
We modeled the working 3D model of the design, however the number of teeth of the gears and their size were larger than our target values, therefore we didn’t exactly use the dimensions of the 3D design to build our medium fidelity prototype.
To increase the size of the gears, first we thought we could just increase the gears in the 2D file with a scaling factor. However, once we tested it we realized that the big and small gears do not match since there is a mismatch between their pitch diameters. We then used the GearGenerator program to test if the gears work together and download the 2D files for laser cutting. We created the box using the BoxMaker program to make it pressed fit. After we laser printed all the pieces, we proceeded with assembly until we realized that we don’t have bearings :/ But we solved this problem by using washers. However we had to make some adjustments for the dowel thickness since the inner diameter of the washers were bigger than the bearing’s. We also laser printed spacers to create necessary spaces for the gears and wheels to be attached to outer dowels.
One notable issue encountered was an imbalance problem, where the weight distribution between the larger and smaller gears caused the mechanism to become uneven and unstable. The heavier weight on the larger gear side outweighed the smaller gear side. Also using washers instead of bearing caused an unstable rotation of the dowels which is a different reason why the mechanism wasn’t working properly. Lastly we had to design the box in a way that it would look like a car and needed a metal piece for the steering wheel.
Our High Fidelity Prototype!
As we proceed with our high fidelity prototype, to overcome the uneven weight distribution between the larger and smaller gears, we made a decision to use a larger gear on the heavier side. This extra-large gear helped counterbalance the weight and stabilize the mechanism. Additionally, we modified the design of the rectangular small gear holders. We increased its length and added teeth to the opposite side as well allowing them to be press-fitted into both the larger gears. This created a more symmetric and aligned system, further improving the stability and balance of the prototype. We revisited our box design since the previous one wasn’t properly press-fitted. Also, since we switched to bearings instead of washers, we reverted to using our original thicker dowels to fit into the bearing’s smaller inner holes. We cut these dowels with a bandsaw which worked pretty efficiently. We were planning to use acrylic however it was a bit problematic due to the issues with the kerf so we decided to cut the front side of the box to expose the internal mechanism and create a triangular top piece, giving the box a more car-like appearance and allowing for a top-down view of the mechanism.
After printing the pressed fit box, we decided to give the box a car like design by adding a windshield to it. In addition we painted the box black to later highlight the car design later with the vinyl cutter. When painting the car black, we ran out of black spray paint! To have a uniform paint job, we went over all of our parts with a black chalk board paint!
(We haven’t tried to use chalk on our car, but are curious to try it out later)
We utilized a vinyl cutter to create windows and decorative elements for the sides of the car. However, this process proved more challenging than expected. We used a plasma cutter to cut our metal piece which is the steering wheel.
Lastly, we painted all the components and completed the final assembly. While the assembly process went relatively smoothly, there were some alignment issues, such as the gears occasionally getting stuck. These problems were resolved through the use of spacers and adjustments to the mechanism.
What we learned
Overall, it was a very fun experience. Through troubleshooting various issues, we developed a deeper understanding of how forces are distributed through the system and how small adjustments in component positioning can have significant effects on the overall functionality of the differential mechanism. This experience provided valuable insights to us into both the mechanical principles behind differential gears and the practical considerations necessary for their successful implementation.
Final Cost Evaluation:
- Cardboard: 1 piece 0.30$
- Wood: about 2 sheets of wood 4$
- Dowels: 2 dowels : 0.50$
- Plasma Cut Metal: 0.45$
- Paint: 4$
- Vinyl: 3$
- Time: 700$ (working 10$/hr)
Total Cost: 700+0.3+4+0.5+0.45+4+3 = 712.25
Link to Slideshow:
https://docs.google.com/presentation/d/1_zipjilGrYJ6HNSU11OQIfsVWJjyrH73pUeJnqPjM1k/edit?usp=sharing
Link to Working Mode:
https://drive.google.com/file/d/1J3ZD9T5NRSnp_wV-d9CFCPBkIa_sn50D/view?usp=drive_link
