RC Baja Car Drivetrain & Chassis
Construction
The construction of this project involves a decision-making process for design, analysis, and manufacturing conducted collaboratively between the two team members. Manufacturing resources such as CNC machining, hand machining, fabrication, 3D printing, and metal/plastic casting are considered. Utilizing a 3D printed mold from the original design. A thermoset plastic will be cast into the 3D printed mold due to its lightweight and resilient abilities. The drivetrain components, crucial for motion, will be manufactured using vertical mills and lathes using steel and aluminum for superior strength over 3D printed parts. The decision criteria encompass factors like strength, ease of manufacturing, time efficiency, size, and cost, ensuring a systematic approach aligned with project requirements.
Image 3.2 - Central Driveshaft for RC Baja Car
The central driveshaft was constructed using a hand lathe by essentially drilling the holes into the two outer ends in order for the pinion gear to be fixed to the central driveshaft. The keyway for the central driveshaft was done using a vertical mill to attach the spur gear that will be driven by the motor. No turning was necessary being the central driveshaft was designed to incorporate standard nominal steel bar stock.
Image 3.4 - Central Driveshaft Pinion Gear
The central driveshaft was first constructed using a hand lathe but then needed to have holes drilled into the ends to press pins to hold onto the pinion gears. The pinion gears were secured using an arbor press and the excess pin material was removed using a grinder. The pin pressed through the pinion and central driveshaft holds very well and secures the pinion from rotating within the central driveshaft.
Image 3.5 - Drawing Tree
Image 3.1 - Test Samples for Material Properties for Chassis
In order to accurately predict and calculate the correct thickness necessary to support the vehicle while still maintaining a lightweight rigid design testing was needed to determine the material properties of the new thermoset plastic. A mold was created and used to pour test samples to ASTM D638-22 standards. These samples were then used within the Instron machine to test for the tensile strength which is used to determine material properties for the chassis.
Image 3.3 - Chassis Casting and Mold
The casting on the top of the image is poured using 65D thermoset plastic. This was created using a negative 3D printed mold. The 3D printed PLA mold is displayed in the bottom left as it was curing. The picture on the bottom right is a PVA test mold. PVA is dissolvable in water. Though the test mold failed, the team felt this would be a better way to create the mold for the chassis as it was quite a challenge to remove the casting from the PLA mold. However, being the PVA failed due to the 65D thermoset seeping through the walls the team still continued to use the PLA mold as it does work just requires more work.
Video 3.1 - Test Sample Molds/Casting and Chassis Print
As displayed above, test samples were required to determine the material properties of the 65D thermoset plastic. First a 3D printed mold was made compliant to ASTM standards. Then the casting was mixed and poured into the mold.
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The second half of the video is the chassis being printed on the Creality CR-M4 printer. In order to test fit assembly and ensure proper fitment of all mounted components the chassis was first printed as the mold and casting process is quite lengthy. The print was performed on the CR-M4 printer as this is the only printer with a large enough bed plate for the chassis.