Alligator Lopper: Gate5
Our group for MAE 277 had the opportunity to familiarize ourselves with the corded Black and Decker Alligator Lopper. This particular device is a branch cutting and trimming device designed for homeowners and the upkeep of their property. It utilizes the technology of an electric powered chainsaw while incorporating a jaw which the user can manipulate open and close. When the user wants to cut a branch, they manipulate the handles and expose the chainsaw to the branch. By clamping the jaws shut around the branch, the user forces the chainsaw into the branch, cutting it. Through the product dissection, we learned that the Lopper was designed with a high level of safety which can be seen in its dual trigger system. Furthermore, most of the product was intended to be taken apart for maintenance or part replacement. This is illustrated in both the simplicity with which the Lopper was designed and also in the list of components the user may purchase online. Further analysis of the product gave us the impression that the components were manufactured using simple techniques that can support a high production rate. Furthermore the materials used in building the Lopper indicate that it was intended to be used in residential areas and would not withstand prolonged commercial use. Assembling the product reaffirmed our belief that the user was supposed to access and maintain most internal components. It also showed us that the product could be modified easily to improve its function and form. These modifications range from small subsystem modifications to larger full system revisions.
Disassembling the Alligator Lopper was the most significant, yet challenging task that the group encountered during this semester long project. This critical task allowed us as a group to get a more detailed understanding of the project. The dis-assembly of the product allowed us to understand the overall function as well as how to divide the functions into sub-functions. We used the top-down approach when considering the dis-assembly of this product.
After the dissection we were required to distinguish the overall difficulty rating, which is reflected by the type of tools that were required to dissect this section, the location of the screws and nuts required to take it apart, and how intuitive the whole dissection process was. The subsystems for the lopper have been arranged in a manner that seems fitting and logical based on user interaction. We came up with 3 major subsystems within this gate, which are the first level subsystem, trigger subsystem and chainsaw subsystem.
These subsystems all contribute to the overall performance of the lopper. The primary focus being user safety, is addressed by the dual motor triggers located on the handles. This requires the user to have full control over the tool before operating the motor. The connection between the power-drive and the revolving chain is crucial to the performance of the product as well. The motor must be able to supply enough torque through the intermediate clutch and transfer it through to the chain. The use of a successful gear ratio is the driving component behind this process.
Understanding the placement of each subsystem allows us to gather knowledge about how production methods and demand have influenced the final product. Beginning with the simplest, the triggers on the handles simply allows for safety, comfort, and functionality. The wiring from these triggers can add to the diversity of location for the rest of the systems. Having the motor, sprocket, and chain track all in the same arm gives added simplicity to the scissor pivot motion that construction of the product suggests.
While disassembling the product it became apparent that the intended use of each component was indicated by both the material used in making the component and also the way in which it was manufactured. The material itself can only withstand so many forces until it ultimately yields so choosing the correct material for each component is imperative to the length of the product’s lifetime. In addition, manufacturing processes have a large impact not only on product durability but also its production costs. Black and Decker had to consider both of these factors when designing the Lopper for residential homeowner use.
The use of high density plastic is prevalent throughout the entire product. It can be found in the entire exterior of the Lopper and within certain subsystems. Its versatility can easily be seen in the wide variety of components comprised of this plastic. The entire outer coverings and handles are made entirely of high density plastic. This is primarily due to the materials high durability and its ability to resist wear. It is also extremely lightweight when compared to a comparable component made of steel or even aluminum. Since the Lopper was designed to be a friendlier looking intermediary between hedge trimmers and a full size chainsaw, the low weight of the product in its entirety is one of the ultimate goals of Black and Decker. Internally, the plastic is used to build the manipulated jaw subsystem. The top handle ends in a semicircular piece of plastic with teeth in it. When assembled, these teeth sit within a semicircular trench which surrounds the motor. When the handles are opened, the teeth rotate around the motor in the trench and operate a gear also made of high density plastic. This gear is directly tethered to the opening jaw. When the plastic gear is rotated by the teeth of the handle, the jaw opens. The use of plastic in this gear subsystem is a testament to the plastic’s durability. It has to withstand the force of the user clamping shut the jaws on a branch. While it is durable enough to accomplish this without failing, it also is extremely light making the weight of the jaw subsystem negligible when compared to the weight of the motor and the gear exchange.
All of the components that were made of plastic were manufactured using injection molding. This is the ideal process when working with plastics since it is an extremely quick process and after the initial investment in the mold, an extremely cheap method. Injection molding this plastic also allows it to have a high degree of complexity in its structure. When taking apart the Lopper, the insides of the handles and the covers were marked with ribbing and internal supports. The anchors for most of the screws used to secure the internal components to the covers were also imbedded in the covers themselves. This high degree of complexity gives rise to plastic components which are extremely durable not in the sense of their material composition but in regards to their structural integrity under heavy duress.
A small number of components were manufactured out of steel. These include the gears and driveshaft used in the gear exchange attached to the motor, the sprocket, chain bar, and also the chain. Steel is by far the strongest material used in this product. It was chosen for these components in particular since these components experience the largest wear in the entire machine. The gears used in the gear exchange are used to convert the motor’s high rpm output into high torque output. This assists the chain greatly when cutting through a material since more torque is required to cut through harder surfaces than higher speed. Due to the speed of the motor and also the resistance to the cutting force of the chain, the gear exchange and sprocket need to be made of the most durable and cost effective material available. What the components gain in durability, they lose in weight. Black and Decker has minimized the amount of steel used in the Lopper, with good reason. Any unnecessary weight on the product reduces its attractiveness to a potential consumer. In the case of the gears, the sprocket, motor and chain, there was no way to avoid using steel. In these instances strength and durability is the highest priority since these components feel the most stress and forces.
The manufacturing processes used to create the steel components are varied based on the component. For instance the gear and the sprocket were both die cast. This is the most cost effective method to work steel into such fine components without changing the material used. The chain and also the chain bar were created using stamping. The chain is actually comprised of a number of different links fastened together with pins. Each individual link was stamped out of a large sheet of steel. These links were bent and filed to form small cutting surfaces. When attached together in a specific pattern, these links for a sharp cutting surface which may be used to cut large branches and other yard debris. The bar was stamped out of a large sheet of steel and was further stamped to give a large slit in the middle of the bar. It is through this slit that the bolts securing the product together pass through. The last category of components that was made of a steel alloy includes all the springs found within the product. There are a total of seven springs used within the lopper and they were formed through a drawing and annealing process. Once the steel was drawn and annealed into a thin wire, it was curled to produce a spring. While two of the springs were tension springs, and the rest of the springs were compression springs, the general process of drawing and annealing is the same.
The final material used in creating the major components in the Lopper is aluminum. Aluminum is a great material since it is relatively strong while at the same time remaining extremely lightweight. Aluminum is not as strong as steel which is evident in its deformability. This makes steel the more apt material when designing components which are consistently under a high amount of stress and force. Aluminum is however much stronger than plastics which makes its use for the gear box and the jaws ideal. The fact that aluminum is also extremely light in comparison with steel makes it a good material to create housings out of. The gear exchange is contained within the motor mount which is made of injection molded aluminum. It is strong enough to contain the gear exchange, but also light enough that it doesn’t add too much to the product’s overall weight. Its durability and low weight make it a perfect material to create the jaws from. The jaw must be strong enough to resist any forces caused from clamping the jaw onto a material but also light enough that it can be manipulated by a plastic gear and handle. Overall the use of aluminum in the Lopper is justifiable since it combines its relatively high durability while at the same time remaining lightweight.
The reassembling of the product is probably the easiest of all tasks need to be performed for this project. Due to our lack of knowledge of mechanisms and systems, it was difficult to assume the functionality of the Alligator Lopper and its subsystems.