Project Summary: Micro Bumper Car Drivetrain Evolution:

I started by designing a miniature bumper car body with a 2x2x2-inch footprint, including a main chassis and a top cover plate secured by four screws. I set up a two-wheel differential drive system combined with a single internal front ball caster for stability, making sure the wheels and caster aligned perfectly on the floor plane.

Then, I selected a 6V, 500 RPM N20 micro gearmotor from Pololu, which has an extended rear shaft. I downloaded the official CAD files and successfully identified the correct part file to bring into my Autodesk Inventor assembly. After analyzing how the motors fit inside the tight chassis space, I realized they are too long to sit end-to-end in a straight line. I drew up a staggered layout concept with spur gears and successfully configured Inventor to generate perfectly sized micro spur gears after adjusting for imperial unit settings. To optimize space even better, I decided to pivot to a vertical motor layout where the motors stand completely upright. I used Inventor’s bevel gear generator to create a pair of tiny 90-degree gears with a perfect 1:1 ratio. I designed and made the entire internal assembly layout myself by constraining the vertical motors and interlocking the bevel gears directly to the wheel axles.

After that, I successfully imported the ball caster and modeled a dedicated, custom 3D-printable base mount platform directly on the chassis floor. Next, I realized that the wheels and axles were completely unsupported, which would cause them to sag and strip the gears under a load. I sketched an internal support tunnel on the chassis wall and overcame an extrusion direction error to successfully join the plastic inward.

Finally, I designed a custom flat-bottomed support block that connects directly to the tunnel and sits flush against the chassis floor to fully support the wheel axle, eliminate the lever arm effect, and keep my bevel gears perfectly aligned under load.