Moving forward is a surprisingly complex task in Baja SAE. Baja SAE subjects vehicles to a unique set of constraints, including a low-powered 10 HP Briggs & Stratton engine; shock loading and rough terrain; and dirt, grit, and mud. All of these factors make drivetrain design a critical factor in Baja SAE racing.
Off-the-shelf commercial and consumer products tend to be designed around applications that require different reduction ratios, or are relatively heavy due to their high power capacities. Off-the-shelf products are not optimized for Baja SAE.
Fig. 1: Dana H-12 FNR, commonly used in Baja SAE
On the other hand, student designed and manufactured gearboxes pose a different set of concerns. They must be precision manufactured; often requiring tooling not available at schools. Designing, verifying, and validating drivetrains requires a huge amount of time from students involved, making it an unappealing project to take on while balancing academics. Furthermore, because off-road racing has few similarities with products standardized for industry – lower reliability requirements, greater shock loading, low power – industrial standards such as AGMA present only a guidelines for design. Many student-designed gearboxes that perform well in competition are not designed to AGMA standards.
BCIT Racing designed it’s own gearbox last year, with a Forward/Neutral/Reverse mechanism. There were important lessons learned from this, such as the nuances of shift-mechanism design. The gear teeth showed little signs of wear, despite the failures that occurred elsewhere in the system.
Fig. 2: BCIT Racing’s custom FNR Gearbox
≤20lbs assembled, dry weight, a 40lb from BCIT Racing’s current gearbox.
One forward gear, approximately 12:1 reduction
CNC aluminum case
Minimal number of independent components.
Field serviceable; including the ability to inspect and replace oil without removing the gearbox from the vehicle.
Must be manufacturable in-house
8in Centre-to-Centre shaft distance
5in width maximum
Fig. 3: BCIT Racing’s gearbox being serviced at Baja SAE Portland
From here, the design process began. Interestingly, after independently studying various gear-design texts, researching, and running calculations, my gear design parameters came out similar to those of last years gearbox designers. Furthermore, after doing more research and talking with students from other schools – contacts I made through in Baja SAE Portland, – I found my gear design parameters were similar to theirs. Phew, I’m on the right track.
Embodiment design began last week, now that we are back at school I have access to Solidworks. I’ve already experienced some issues regarding permissions to modify ToolBox parts (gears) due to our school licensing – I’m working on remedying these with faculty. The case is being designed so that it can be manufactured with a 3 axis CNC so that the critical-features of each half may be manufactured in one setup.
So far, it looks like we are on track to achieve the design specifications. CAD renderings are under-wraps for now, but will be released soon. I promise the final design will be worth taking a close look at.
Fig. 4: Shigley’s Mechanical Engineering Design lived in my backpack this summer