Gate 4 Group 27 2012

Revision as of 12:08, 30 November 2012

Introduction

In Gate 4, we will reassemble the drill, and discuss in detail the complexity of reassembly. We will also discuss a mechanism of the drill that is used to generate a specific motion. In addition, we will suggest 3 system changes, keeping the GSEE factors in mind when considering changes.

Cause for Corrective Action

During Gate 3, the plan of action had worked out well, and the changes made after Gate 2 proved to be useful. Consistently throughout the project, we have been using email as the main source of communication for allocating tasks, and for describing the overall plan for the project. Email was also used to give a record of meeting times. Texts and phone calls were used for more immediate communication, in particular with regards to meeting attendance. As for planning the project, deadlines were set for each section ahead of the actual due date of the project, so that there would be time for revisions. Another thing that was consistent throughout the project was that one person set up the Wiki page, complete with headlines and titles, so that the whole page would be more logically ordered and more cohesive throughout. This also prevented redundancies, as well as out of place information. These practices, which were done throughout the project, have proven to be very effective in creating a thorough report for the drill.

The most significant revision in Gate 3's project plan was in the way that tasks were allocated to the different members. Gate 3 was structured in a way such that certain parts needed to be done before others could be done. Because of this, those parts which were prerequisites for other parts of the project were to be completed by either the group at a meeting, or an individual who had reliably produced work on time in the previous Gates. This proved to be useful, as when it came time to do the project, some of the group members had missed the deadline by which the other members had agreed to have their sections submitted. As a result of this allocation of tasks, the project was able to continue, with only slight inhibitions. This practice will be continued in Gate 4, but with some refinement in the allocation of tasks. Gate 4 does not have parts that have to be done in a sequential order, and as such the allocation will be based on the point value of each section. Those who scored the highest on their sections in the past were given the sections with the highest portion of the grade. This way, if parts of the project are late, incomplete, or do not meet the satisfactory level, the overall impact on the grading will be less.

Product Reassembly

Step	Description	Difficulty	Tool Used*	Pictures
1	Reinsert trigger spring	Easy	N/A
2	Reassemble trigger box	Easy	N/A
3	Reinsert spring tensioner, spring and washer	Medium	N/A
4	Reattach position collar	Medium	N/A
5	Reattach metal position ring	Easy	N/A
6	Reattach c-clip to clutch head	Medium	Allen Wrench and Combination Pliers
7	Reattach grip ring to chuck	Medium	Flat Head Screwdriver
8	Reattach chuck to clutch with allen wrench	Hard	Allen Wrench
9	Reinsert star drive bit into drill chuck (left hand thread)	Medium	Star Head Screwdriver
10	Reinsert secondary planetary gears into gearbox	Easy	N/A
11	Reinsert planetary gears into gearbox	Easy	N/A
12	Reinsert the eight ball bearings into the gearbox	Easy	N/A
13	Reattach motor cover to motor	Easy	Flat Head Screwdriver
14	Remount motor with screws using phillips head screwdriver	Easy	Phillips Head Screwdriver
15	Reattach motor washer	Easy	N/A
16	Attach planetary gearbox to motor	Easy	N/A
17	Reattach motor/gear assembly to clutch/chuck assembly by rotating and then pushing	Medium	N/A
18	Reattach motor connections	Easy	Flat Head Screwdriver
19	Place connected subsystems into plastic shell	Easy	Combination Pliers
20	Reattach plastic shell piece while making sure wires do not get pinched	Easy	Flat Head Screwdriver
21	Reattach metal crimp on battery port	Easy	Flat Head Screwdriver
22	Screw in the seven right sole housing screws with a phillips head screw driver	Easy	Phillips Head Screwdriver

Mechanisms

The planetary gear set is a mechanism used in the drill that modifies and condition rotational mechanical energy. Its technical name is Epicyclic Gearing, however it is more commonly known as planetary gears. The purpose of the mechanism is to change angular velocity and torque in a rotational system. As torque increases, angular velocity decreases. This is a common purpose shared among all gear sets, including those that are not of the planetary variety. The advantage in an epicyclic gear set is that several sets of gears can be placed on one another, stacking in a cylinder shape. This cylinder shape was desirable in the drill, as the motor, clutch, and chuck are all cylindrical shapes, and thus the cylindrical shape of the planetary gears fit well with the other components. The gear set is composed of a central sun gear, surrounded by two or more planet carrier gears, and then surrounded by a single annulus. Of the three different kinds of gears, one has to be held stationary so that one can drive the other. In the example of our drill, the annulus is held constant by the clutch, and the planet and sun gears rotate. The motor turns the sun gear, causing the planet gears to move. When the drill becomes stuck, the clutch slips, and then the planet gears become stationary, and the sun gear and annulus rotate. The equations relating the different pieces are as follows.

Number of teeth on gears to Angular Velocity

Design Revisions

Interchangeable Chuck Piece
Cordless drills when used in conjunction with a socket set usually do not have the amount of torque required to loosen or tighten screws, bolts, and nuts that are corrosively “frozen” or over-torqued, or drive screws into hard metal and other strong materials . One solution to this problem would be to design a system in which the chuck is a removable piece that can be interchanged with an impact driver mechanism. This driver would be very similar to that of the regular chuck except that it would contain another set of impacting gears that would activate once the torque required to continue driving rises above the torque that can be generated from the rotational power of the drill itself. These gears increase the torque output of the drill significantly in a way similar to that of the adjustable clutch. Throughout this use of the impact driver piece a hammer attached to the drive shaft rapidly pounds into an anvil, which is attached to the bit. These powerful strikes will supply the drill with the extra torque needed. Other impact drivers work at around three thousand blows per minute or fifty blows per second. This translates to about one- thousand inch ponds of torque, doubling the amount of torque capability of the drill attachment. The downfall to the impact driver is that it is inaccurate and sometimes too powerful for the job, so having the option to use the just drill attachment gives the user the ability to drill precise, small holes when needed.

Factors Addressed

• Societal- The addition of the impact driver attachment adds significant range to usage purposes of the drill. It widens the intended customer base from homeowners and hobbyists to industrial workers, auto mechanics, construction workers, and other labor jobs.
• Economic-Although the addition of the impact driver attachment makes the drill more expensive, it’s still cheaper than the combined cost of buying a drill and an impact driver separately. In economic conditions in which a customer doesn’t have a lot of money to spend on power tools, the combination of the impact driver and drill into a single package comes as an easy way to for a customer to get “more for less.”

Variable Gear Box
One of the other system level change that can be incorporated is the variable gear box replacing the planetary gear box. The variable gear box improves the performance and increases the battery life. It improves torque which acts as an added bonus to the costumers looking for drill at the same price point. It lowers wear and maintenance as the system reduces the moving mechanical parts. From an engineering point of view the variable transmission device is preferable to conventional gearbox with fixed gear ratios because variable transmission allows varying combinations of speed and torque to suit the condition and operators preferences. The change to the gear box requires change in the clutch. The clutch is changed so that it now feature the ability to slide the gear into position without affecting the handling of the drill during the drilling process. Such a system level change can positively affect the overall performance and handling.

Factors Addressed

• Societal- The improved performance and added functionality adds significance to the usage profile. It widens the intended customer base from homeowners and hobbyists to industrial workers, auto mechanics, construction workers, and other labor jobs.
• Economic- Cost of changing the gearbox could significantly increase the cost based on the complexity, size and its mechanism, but with large-scale production and improved manufacturing methods, the cost can be reduced to match the cost of the regular gearbox. But with less complex or simple variable gearbox, the cost can be significantly reduced to its counterparts, which makes the drill much cheaper. In economic conditions in which a customer doesn’t have a lot of money to spend on power tools, this package comes as an easy way to for a customer to get “more for less.”