Remote Control Car
Project Background
In high school, I took a class called Technology Education in which we were introduced to many of the technologies behind everyday products and processes. One of the projects that we were given in class allowed us to assemble a remote-control car far more powerful than any cheap toy-store car that I had driven in the past. I took a picture of it and upon examining it later on, I realized how simple the circuitry within it was. Besides sending signals remotely through air, every circuit component driving the system was something that I had dealt with before. I set out to build my own remote car from scratch using components available to me at home or for a low price including repurposed scraps and a few parts that I found online.
I began by purchasing a 280-watt motor because I was going for a completely overkill hobby-remote-car design and didn’t much care about energy efficiency, but I knew that I would rather use an electrical design than an engine-driven design. After doing the math, I concluded that my car would be able to hit a maximum speed of around 40 miles per hour, far higher than any remote car that I had previously encountered. Using simple nuts, bolts and screws, I mounted everything to a cutting board which acted as my structural base. I chose a belt-drive because of its low profile and low noise production relative to that of a chain, which was the other potential driving option.
This project was my first introduction to pillow-block bearings which I used to support the rear axle of the car. I had never heard of open-source microcontrollers at the time that I began this project and so I had no idea how easy it would be for me to program my own Arduino or something similar with transistors, relays and radio peripherals to communicate with and control the car. I chose to compensate for that lack of a proper solution by doing the best thing that I knew how to do, which was splicing systems that had features that I desired with my own concepts.
I salvaged the mainboards from two cheap remote cars that I had tested to make sure that they were working and mounted them on my own car to control my motor. I came close to finishing this project, as the only thing that I didn’t complete was the steering control, but I decided to end the project there. By the time I cut the project off and scrapped the car for parts, I had learned about microcontroller solutions better suited for the tasks that I desired performed than the cheap remote car circuits that I had used and didn’t want to proceed with my original design.
I don’t know if I’ll ever pick this project back up. It’s difficult to convince myself to go back to it since I have larger ambitions now than driving remote cars in my spare time, but as it could be fun and educational still, I may start again from scratch eventually. For my age when I worked on this project, the car that I produced was the best that I could do, but I could never continue the project using my original attempt as a starting point. The materials and workmanship are both subpar when compared to my current standard of quality, and I would much rather 3D model and precision manufacture my own parts in a new superior version.
Detailed Description
I wasn’t well enough educated at the time to know how to read and interpret voltages on the remote car mainboards and then use those pins to drive transistors that would control the motors on my car, which is what I would do if I were using those remote car mainboards now. That solution would have been far more elegant than what I settled on. Instead, I set up a mechanical switching system using the original low-power hobby motor that originally controlled the store-bought remote-control car to instead flip switches that would tell my car to move forward and backward.
Using clever wiring and two high-current switches, I was able to set them both to be normally closed (thus locking the motor when not being accelerated), one to allow current flow through the motor in one direction when flipped, and the other to allow current in the other direction when flipped. This effectively gave me direction control, but I needed to actually flip these switches somehow for them to be useful. I constructed a lever attached to the rotor of the hobby motor which, when “accelerated” forward by command of the mainboard receiving control signals from the remote, would flip one of the switches that would then power my car’s motor in the “forward” direction. The lever would flip the other switch when the car was told to accelerate backwards, and that switch would turn on the motor in reverse, thus driving the car backwards.
This took care of forward and backward control of the car, which I tested, and it did work, but it also had the side-effect of braking the car’s back wheels instantly whenever they weren’t being powered whether I wanted them to or not. For steering control, I planned to do something similar, except instead of throwing switches, I desired to tug a rod either with a motor or a servo left and right, towing and changing the aim of the front wheels. This design was based on the concept of the Idler arm, Pitman arm, center link and tie rods mechanism found in real vehicles.
I had a center link attached to each wheel at a ball-in-socket joint with around a two-inch moment arm from the swiveling axis of the wheels. To form the swiveling axis, I installed two vertically-oriented ball bearings into the base, each with a 3/8-inch shaft protruding toward the ground. Two through holes were drilled in each shaft, one for the idler rod components and one for the axle on which each wheel would ride. The ball bearings were pressed into place in the car’s base with their axes oriented vertically, and to hold them there, I riveted two washers in on either side of the base.
To attach the back wheels to the frame, I ran a bolt through each wheel’s center-hole and locked them together with hex nuts, used a die to form threads on the end of my rear axle, and connected each wheel to its ends using couplers with the same thread pitch. To prevent the threads from loosening, I drilled holes through the axles and couplers, then ran cotter-pins through them to block rotation within the threaded sections.
In my later attempts at completing this project, I planned on driving the center link connecting the front wheels to the left and right to steer the car with a servo arm which would attach to the center of the rod via springs. I never did end up correctly wiring the servo that I planned to use to the RC-car mainboard, which would have been essentially the last step in the project.
Though I did try and fail to connect the servo to the mainboard in multiple ways, I learned at that point that servo control is more complicated than motor control due to a servo’s position encoding and was unable to reconcile that incompatibility with my limited skillset. I also had no good way to mount my servo, a problem that would have been easily remedied by 3D printing, which I was unable to perform in any capacity at the time. If I were to begin building this project again from scratch, I would use quite a few 3D-printed components for non-load-bearing components, paired with precision-machined structural components.