PROTOTYPE (CAD)
1ST PHYSICAL PROTOTYPE
GEAR CALCULATIONS
The mechanical advantage at the end of the drill changes based on two factors: the orientation of the handle and chuck as well as the gear disk being used. The handle extends 3 inches from the central axis of the drill. Assuming the user inputs 5 pounds of force to the handle, there is 15 inch-pounds of torque applied. Assuming the gear disk, handle and crank are setup to drive the 1.5 inch center gear, we can say that there is a mechanical advantage of 2. This is because d(out)/d(in) = t(out)/t(in) = MA. The diameter of the output (the inner planetary gear) is 3 inches and 3/1.5 = 2. The bevel gears don’t affect the mechanical advantage of the gears because the output diameter and input diameter are the same. The center gears act like idle gears. The purpose of the bevel gears is to reverse the direction of the torque, which gets flipped back to the right direction due to the planetary gears. This yields an output of 30 inch-pounds of torque assuming there is no friction in the system. By switching the chuck and the handle while keeping the same gear disk, the mechanical advantage is inverted, creating a mechanical advantage of 0.5 and an output of 7.5 inch-pounds of torque. Although the torque went down the speed at the end doubles because MA = Speed(in)/Speed(out). This means that every rotation of the handle causes two rotations of the chuck. With the second gear disk is being used and the center gear is being driven, the mechanical advantage is d(out)/d(in) = 3/.75 = 4 meaning there is an output of 60 inch-pounds. At the same time, the output spins 4 times faster. With the same gear disk, we get a mechanical advantage of ¼ by switching the handle and the chuck. This means there is only 3.75 inch-pounds of torque, but the speed of the output is 4 times faster than the input. There are benefits to having both high and low mechanical advantages. If the mechanical advantage is greater than 1, there is more power at the output making tasks such as screwing or unscrewing easier. If the mechanical advantage is less than 1, then the torque lowers, but the output speed increases making tasks such as drilling holes easier.
PROTOTYPE PROOF OF CONCEPT VIDEO
Our Product In Action
DESIGN OF EXPERIMENTS
In order to test the effects of a changing gear ratio and mechanical advantage we designed a theoretical experiment to measure the effects of changing those variables
BILL OF MATERIALS FOR THE PROTOTYPE WITH AN APRIORI COST ANALYSIS
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MANUFACTURING ANALYSIS AND ANALYSIS OF APRIORI COST ANALYSIS FOR THE PROTOTYPE
TOP 10 CUSTOMER REQUIREMENTS
Easy to use
The new design is less ergonomic than the old design. The old design had both a handle for the crank and a second handle to steady the drill. The new design has a detachable crank handle, which could detach during use and cause injury. In addition, there is no additional handle to stabilize the drill during use.
Easy to maintain
The new design is easier to maintain than the old design. The old design could not be disassembled without destroying it. The new design allows the removal of the chuck, the crank, and the planetary gear disk without destroying the product.
Affordable
The new design has a significantly higher fully burdened cost than the old design, because the new design has significantly more individual components, making it more expensive to manufacture and assemble than the old design.
Durable
The new design is significantly less durable than the old design. The old design was almost entirely made of steel and was assembled via press-fit and rivets. The new design has a larger number of components, many of which plastic components made of PC, PET, and ABS. Therefore the individual components are weaker than that of the old design. In addition, the new design relies heavily on snap-fits, which are weaker and easier to disassemble than press-fits and rivets.
Reliable
The new design is less reliable than the old design. The new design contains many more components than the old design, especially with respect to the gears. The old design had only two gears, the gear attached to the crank, and the bevel gear that drove the crank. The new design has a planetary gear system and a differential made of four bevel gears. Therefore the new design has more potential points of failure than the old design.
Portable
Since the new design was made with ease of disassembly in mind, the new design is more portable than the old design. On the other hand, the old design has only one removable component, the chuck.
Safe
The new design is more dangerous than the old design. The old design had both a handle for the crank and a second handle to steady the drill. The new design has a detachable crank handle, which could detach during use and cause injury. In addition, the lack of a second handle to stabilize the drill can also cause injury.
Drills a variety of materials
The new design can drill a greater variety of materials, because of its ability to vary gear ratios. As a result, the new design can vary the torque it applies to a workpiece and the speed at which it spins.
Fits a variety of tool bits
The new design and the old design fit the same number of tool bits, because they use the same three-jaw chuck.
Aesthetics
The greater symmetry of the new design should attract customers. The old design is asymmetrical, with the crank perpendicular to the shaft.
PDS REQUIREMENTS
Fully Burdened Cost
The target fully burdened cost is 40 dollars. The actual fully burdened cost is $78.53.
The high fully burdened cost is in large part driven by the sheer number of individual components (61), especially the gears. Due to their importance to the functionality of the design, it is extremely important that gears be manufactured to precise tolerances. As a result, the large number of gears greatly increases manufacturing costs. In addition, the large number of parts makes the product harder to assemble, requiring more workers and increasing opportunities for defects to emerge.
Number of Gear Ratios
The target number of gear ratios is three. The new design currently offers four. There are currently two built planetary gear disks. Each planetary gear disk offers two different gear ratios, because the positions of the chuck and crank can be interchanged such that the chuck can be driven by the ring gear or by the sun gear.
Gear Disk Changing Time
The target changing time is one minute. The gear disk can be changed with an average of twenty seconds.
Weight
The target weight is 2 lb. The new design is 2 lb.
Patriotism
The goal was to make at least some parts in the US. We decided to outsource to China.
In conclusion, the new design met expectations laid out in the PDS, with the notable exception of the fully burdened cost.
Compared to the original design, the new design is much more expensive and complicated, with many potential points of failure, but offers great flexibility of use, due to the variable mechanical advantage of the drill. Good quality control will be key in implementing the new design.
UPDATED PRODUCT DESIGN SPECIFICATION
After running a cost analysis of our prototype and testing our prototype we updated the PDS to match our observations and collected data
FINAL CONCLUSIONS ABOUT OUR PROTOTYPE
In terms of cost, our redesigned hand-crank drill has a much greater cost than that of the original model. We have evaluated the cost at $78.53. There is some discrepancy in the evaluation because we have calculated the cost based on manufacturing certain parts such as the gears, by die-casting, ourselves which is not likely what a manufacturer would do. Instead they would purchase these products from outside manufacturers in order to keep costs lower. The cost was also driven up by the larger than expected number of individual parts. The cost of the original hand-crank drill was $27.54, but this drill does not have as many advantages and as much functionality as our redesigned drill.
When considering functionality, our redesigned hand-crank drill is capable of much more than the original product. First, we can invert the mechanical advantage by swapping the location of the crank and the chuck. The orientation seen in Figure 18 exemplifies the location of the chuck and crank with a high mechanical advantage. If you were to flip the chuck and crank you would achieve a much lower mechanical advantage: in fact, the inverse mechanical advantage. This is an important aspect of our drill for the reason that it allows consumers to achieve different goals. For example, if one were drilling a hole, he or she would want a low mechanical advantage to achieve a greater speed, therefore he or she would attach the handle to the ring gear and the chuck to opposite side. If after drilling the hole he or she desired to put a screw into that hole, he or she would then flip the chuck and the crank in order to achieve a higher mechanical advantage and a slower speed. This helps the consumer achieve his or her goals more effectively and more efficiently. Inverting the chuck and the crank would not be possible if it was not for the gear box near the center of our product as seen in Figure 18. This gear box causes the crank and chuck to spin in the same directions no matter the location of each. Also, you can switch out different gear disks as seen in Figure 1 and Figure 4. They have snap fits that allow them to be easily interchanged for the desired mechanical advantage. This gives the consumer even more freedom to accomplish different things and gives them more variance in terms of mechanical advantage.
Our fully manufactured product would be of higher quality than the original product, but that comes with a much higher cost and longer manufacturing time due to the fact that there are many more parts in our redesigned drill.
Our hand-crank drill would take more time and money in order to manufacture, and involves a series of manufacturing methods. Therefore, it would have a greater dampening on the environment. Outside of the manufacturing, once our product is in the hands of the consumer it will have zero environmental impact for it requires no energy source or and is powered strictly by the raw strength of the consumer.