My Project Log: The Micro Bumper Car Evolution

Phase 1: Chassis and Drivetrain Layout

I started by designing a miniature bumper car body with a tight 2x2x2-inch footprint, consisting of a main chassis and a top cover plate secured by four screws. For movement, I chose a two-wheel differential drive system paired with a single front ball caster for three-point stability on the floor.

I selected a high-quality 6V, 500 RPM N20 micro gearmotor from Pololu. When I brought the CAD files into Autodesk Inventor, I quickly realized the motors were too long to sit end-to-end in a straight line inside my small chassis. I first explored a staggered layout using custom-generated imperial spur gears but ultimately found a much better solution: flipping the motors completely vertical. Using Inventor’s bevel gear generator, I engineered a compact 90-degree, 1:1 gear mesh to transfer power directly from the upright motors to the wheel axles.

Phase 2: Structural Integrity and Gear Protection

Once the layout was set, I noticed a major mechanical flaw: the wheel axles were completely unsupported, meaning the weight of the car would cause them to sag, bend, and instantly strip the fragile bevel gears. I fixed this by sketching an internal support tunnel on the chassis wall, overcoming an Inventor extrusion direction error to merge the plastic inward.

To completely eliminate the lever-arm effect on the wheels, I designed a custom, flat-bottomed support block that bridges the gap between the tunnel and the wheel hub. This pillow-block style support sits flush against the chassis floor, absorbing all driving impacts and keeping the bevel gears perfectly aligned at 90 degrees.

Phase 3: Electronics Packaging and Component Selection

With the mechanics locked down, I turned my attention to the empty space on the front deck to solve the internal packaging puzzle. I decided to maximize this room by opting for a large, high-capacity 1S LiPo battery in the standard 752540 or 802540 form factors (roughly 2x1 inches), ensuring long runtimes and a low center of gravity.

To save even more space, I selected the ultra-compact Pololu Baby Orangutan B-328, which conveniently combines a microcontroller and a dual motor driver onto a single tiny board. Because an official 3D model didn’t exist for this board, I used the engineering “block-out” method to model its exact 1.2x0.7-inch dimensions in Inventor, allowing me to successfully map out the electronics bay layout.

Phase 4: Wireless Control and Tournament Planning

Finally, I shifted focus to how a player will actually drive the robot. I mapped out the electrical paths connecting the battery to the controller, and the controller outputs to the N20 motors. To make the car fully drivable via a handheld remote, I integrated a wireless receiver into the layout.

Anticipating a 4-player bumper car soccer tournament, I analyzed potential radio interference to make sure the match wouldn’t turn into a chaotic ruckus. I ruled out cheap Infrared (IR) remotes because they blast identical light signals that would accidentally control every car at once. Instead, I established that using a digitally bound 2.4GHz RC system or paired Bluetooth modules will guarantee secure, 1-to-1 connections, allowing all four robots to compete fiercely without interfering with one another.