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Objective:
Objective:
I am fascinated by RC cars, and I always wondered if I could make my own RC car with mostly 3D printed components. I decided to make an RC car from scratch, and it was far more complicated than I originally thought.
Brainstorming process:
Brainstorming process:
I researched several the key parts of existing RC cars, including some of my own cars, and disassembled one that didn't work anymore.
The key components I found were:
Main Chassis
Drive shaft with gear reduction
Front and rear differential
Suspension assembly with 4 bar linkage
CV joints to transfer power from differential to wheel that can rotate with suspension
Strong wheel bearing joints
Steering linkage for front drive assembly
Design:
Design:
I designed my first version of the RC car in the CAD program Fusion 360. I first tried to make the rear drive assembly as it was the simplest since it did not need to turn. After printing it, the suspension properties worked, but there was a severe problem with the deflection of the exterior wheel (almost 30 degrees). This would render the car useless.
Rear Drive Assembly V1
Rear Drive Assembly V2
So I went back to Fusion 360 and redesigned the entire assembly, making the 0 tolerance joints on the inside of the joints, and the loose fit rotary joints on the outside (Y split on the linkage arms). Additionally, I stiffened up the arms and the general structure to prevent bending. I also made the differential housing (centerpiece) screw together from top to bottom instead of front and back to ensure the assembly would take the massive forces of taking a jump or crashing.
Steering Drive Assembly V1
After modifying the rear assembly introducing a steering linkage, I ran into the problem of determining a strong enough geometry that also did not tow in or out when the suspension travled up and down. I redesigned the steering linkage arm to be parallel to the main linkage arms so that when there was suspension travel, the steering would remain constant.
Steering Drive Assembly Steering Link V2
Final Design
Assembly:
Assembly:
Putting the chassis together in real life revealed an issue that was not fully accounted for during the design process. Although I had considered assembly order and clearances, I did not leave enough room for the fully assembled gear train to fit without interfering with the axle guard. To fix this, I modified the frame with a Dremel, sacrificing a small amount of rigidity to make assembly possible. After making these slight manual adjustments to the chassis, I was able to assemble everything successfully. In the end, the parts fit together well, and after lubricating the internal 3D printed driveshaft gears and differentials, the car was ready to go.
Drive Shaft Assembly
Full Chassis
Fully Assembled RC Car
All the Failed Parts!
Results:
Results:
The car performed very well overall. The chassis was rigid enough for stable driving, reached a top speed of 30 mph, and was strong enough to survive jumps. Compared to the first iterations of the drive assemblies, the final design also achieved a significant reduction in linkage backlash, though there was still room for improvement.
For a second iteration, I would widen the suspension linkage pivots to give them more leverage against twisting moments in the suspension, especially under the large forces created when power is delivered to the wheels. I would also redesign the chassis with assembly in mind, likely switching to a single base plate with bearing pillow blocks clamped from the top rather than using press fits. Finally, the steering linkage connections are relatively thin, so increasing their cross sectional area would improve strength and durability.
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