Mechanical Engineering with a Remote Control Car

The goal of this project was to design and build a remote controlled car. The idea was to first design the car on paper, including the parts, their locations, and their overall purposes. Using our own previous knowledge of cars in general combined with the teachings of ProEngineer, computer software specifically designed for threedimensional CAD drawings, it was possible to research different aspects of cars and create as well as buy the various parts compatible for an R/C car. We were motivated by our passion for engineering and the overall satisfaction of driving our end product. Using the ProEngineer software, we were able to design and replicate the components of our very own miniature car. Using nothing but two sets of calipers, we were able to get dimensions for each part of the car and replicate the pieces into the program. Calipers are measuring tools which can make precise distance measurements down to a thousandth of a millimeter. Using our intricate drawings on the program, we used a “3-D Printer” to convert our 2-D drawings into 3-D plastic parts. Introduction A remote controlled car is a car that uses radio frequencies as a source of control. The first R/C model was a Ferrari 250LM built in a 1:12 scale. This model was then followed by the company’s (El-Gi) next R/C Ferrari P4 built in a 1:10 scale. R/C cars started off reasonably primitive back then, having the bare minimum of parts and being shaped as dune buggies, then later evolving into monster trucks [5]. It wasn’t until the mid 1980s that the United States got actively involved in the remote controlled car industry and the structures became more and more involved. They went from just a simple motor and axes, to a fully functional miniature car. Manufacturers began to give them complex systems including ball bearings, transmissions, shock absorbers, and disc brakes. The transformation happened rather rapidly and is still evolving today. Thus began the basis for our project, to design and construct our own remote controlled car. The only thing we had to use was a set of calipers and a totally new program. These circumstances were not exactly in our favor, but we believe that we carried out the planning, designing, drawing, and engineering phases of the task to the best of our abilities. Background Information/Related Work The first few days were devoted to mastering the basics of a single, vital program. “Pro-Engineer,” as it was called, would be used primarily to execute the CAD and CAM functions. Rapid prototyping is an additive fabrication technology used for building physical models and prototype parts from 3D computer-aided design (CAD) and medical scan data. Unlike CNC machines tools, which are subtractive in nature, these systems join together liquid, powder, and sheet materials to form complex parts. Layer by layer, they fabricate plastic, wood, ceramic, and metal objects based on thin horizontal cross sections taken from a computer model [3]. A rapid prototyping machine reads the data from the CAD drawing and lays down a liquid material layer by layer until the threedimensional model is completed. The material used to make the part has a high melting point; in contrast, the material used to support the structure as successive layers are added possesses a low melting point. Upon completion, the machine heats the model until the support material melts away, leaving only the plastic prototype. Usually, the overall process can take anywhere between three to twenty hours, depending on the size and intricacy of the piece being built [4]. During the early design phase, we used one of our own remote-controlled cars as a template. An HPI Evo-3 car (Figure 1) was examined as a reference. This specific model employed a suspension system [2]. However, due to the time constraints, engineers of the car opted for a rigid body design which would require fewer parts. Overall, the HPI Evo-3 served as a reference to work off of. After completing observations and examinations, the parts deemed essential – motor, battery, differential, receiver, speed control, and wheels – were purchased. In order to protect the parts from damage and overheating, casings were constructed (using Pro-Engineer and the rapid prototyping machine). Each casing, though different in design, featured 3-millimeterthick walls. All were customized to suit the needs and orientation of the individual part. For instance, the battery casing was build to support the battery in a position that would permit it to lie on its thin side rather than its flatter, blunter surface as to minimize surface area consumed on the board of the car. As a personal flair, initials were engraved on one of the casings. In order to ensure that there would be ample space for each part, measurements that allowed for ample space were taken. From there, the basic blueprint of the car, including the locations of the motor, speed control, and other essential parts, could be constructed. In determining the locations for Figure 1 HPI Evo-3 the motor, battery, and speed control, it was important to account for the fact that these parts tend to heat up while the car is in drive. We also needed to find a way to secure each part to the body itself and make sure that they did not affect each other negatively. Overall, spacing was essential to allow for tolerances. Under a budget constraint of four-hundred and fifty dollars, some parts had to be manufactured, rather than purchased, using the rapid prototyping machine. Measurements of other parts such as the drive shaft support, which had no precedent from which measurements could be taken, relied on careful estimation based on related parts, such as the drive shaft, so that they would fit properly. Specifically, the remote-control car relies on two batteries: one 7.2-Volt battery and one mega-volt battery. Airplane tires, though not optimal in terms of efficiency, were chosen because they are more cost-effective than other options. Furthermore, since four-wheel drive proved too complex, only rear-wheel drive controls steering. Two back wheels which remain responsible for directional control are connected to a drive shaft of diameter 0.25-inches that rests on a support consisting of four pillars, each with 0.27inch diameter holes. The rod spears through these openings, allowing the pillars to hold it up. Experimental/Engineering Design First we identified the problem, which was manufacturing a radio controlled car. We also had constraints that we had to abide by. Our budget for the radio controlled car was only 450 dollars. This included tools that we needed to buy, like calipers. We also had a time constraint of three weeks. The three weeks included the time it took to learn how to operate the Pro-E program. Along with the three week time constraint we only had limited time every day to use the CAD software in the computer labs. Another constraint was that the rapid prototyping machine only printed out ABS 400 plastic. This meant that our designs had to compensate for the brittle nature of the material. We had to consider these factors in our design of the car. We needed to design several systems that were critical to the car. The steering, drive train, and the electronic component layout were critical systems. The money gave us some leeway as to what we could buy as well as how much we would be forced to make. With the constraints recognized, we moved to the design solutions process phase of our project. We had several differing designs for the various components in the car. One of the biggest problems was deciding which designs were the best, and most realistic. There were, however, many crucial systems and parts to be made for the car. We decided to start from the ground up when building the car. This made the base the first part we worked on. We had the options of buying an acrylic plate and cutting it into what we want, modeling one and printing it out, or simply buying a premade frame. We settled on buying an acrylic plate and cutting it out because we figured that the ABS 400 provided by the rapid prototyping machine would not be strong enough to support the stresses the car would undergo during use [1]. We also decided against buying a premade frame because it would cut into our budget and it was against the overall engineering aspect of this project [6]. The next system up for discussion was the steering system. The steering had to be reliable but not so complex that time would become a problem. Furthermore, we tried to keep from making one part hold too much stress during turns. We came up with many variations of the steering. One idea consisted of a single steering bar which would attach to the bearing that the wheel is mounted to. This idea was discarded because it put a lot of stress on the solo steering bar which would have to control not only one, but two wheels. The problem was that if this one bar were to fail, the entire car would become immobilized. Another idea was to have two bars, similar to the first idea; instead the single bar would be cut into two. This idea was also put to rest because the stress that each bar would have to sustain would take the ABS plastic too close to its deformation point and possibly end up snapping or bending it. The final design was comprised of two bars that spanned across the width of the car. This design prevailed because it shared the load over two separate bars, thus lowering the probability of a failure. Also because there were to separate bars, if one bar did fail the car would still be able to maneuver and run until the necessary repairs could be made. Another problem that had to be resolved was how we were going to get the power from the motor to the driveshaft. All the ideas that were brought up had the potential to be successful. The overall question was, “Which one would work the best?” The first proposal was to have two pulleys and have a belt that resembles an oring to connect them. This idea was heavily considered but was ultimately thrown away because there was a major concern that the belt would possibly slip. Another idea was to connect them using a timing belt. This was a great connection system because the teeth on the timing belt do not slip like regular pulleys. However, the timing belt would have to be custom made for our application. We would not have been able to afford such custom parts, and in response, the idea was not put into action. The final proposed idea was to use gears to make the connection. This idea was ideal because it not only allowed use to make the connection but it also allowed us to make the gear reduction that we needed to design in order to take advantage of the motors ridiculously high number of revolutions. We also had access to several gears that were donated by past project groups. The suspension system brought about many challenges and its many design solutions proved to be controversial. Suspension was not a necessary system, but its benefits were substantial and highly noticeable. No matter which idea we came up with, it would be complicated and very difficult to incorporate suspension into the radio controlled car. Our suspension ideas spanned from having each wheel have its own independent suspension to each pair of wheels having its own suspension. We began to design a suspension system that allows each wheel to rotate freely. We began to design the parts for our suspension system when we came to the realization that the time needed to make the suspension parts would be greater than the time we actually had to work. We then chose to go with a rigid body type, free of suspension. Modeling Parts with Pro-Engineer After we had a general idea of what we wanted the car to look like we began to work on Pro-Engineer. We spent the most part of the first week learning how to use Pro-E to create parts and assemblies. Some of us were quick learners, mastering the program within the first few days, while others struggled. The first things that were modeled on Pro-Engineer were the cases for all of the electronic parts that were needed to run the car (Figure 2). Cases were made for the battery, speed controller, and the transmitter. Each of these cases were required to fit their respected part snuggly within them and they also needed to have holes at the bottom to fasten them to the piece of acrylic that was being used as a base. These cases were also made with walls with a thickness no less than 3mm to withstand vibration and other impacts that the car will have to endure