Gate 4 - Product Explanation and Reassembly - Group 6 2012

• Serve as a point of contact for instructors
• Compose and disseminate communication between group and instructors
• Create a continuum of evaluation for group interactions

• Continuous documentation of group’s interactions have created an organized resource for further evaluation of group interactions and provided a framework for future decisions on how work is to be divided and delegated

• Gate 4 has proved challenging in terms of documenting group interactions. For this Gate, the majority of the work has been done in small group settings, many of which have not been attended by the Communication Liaison. Fortunately, group members have been very responsive in providing feedback as to how work for the Gate has been progressing, and assistance has been sought on a regular basis for the resolution of various challenges.

• Make appropriate divisions of work for larger sections of Gates and delegate tasks accordingly
• Set timeline for work to be done, including internal group due dates for work leading up to class due dates
• Arrange group meetings, including coordinating group member availability and booking learning space in campus libraries as necessary
• Preside over group discussions and mediate group conflicts

• Group time and physical meeting space has been consistently coordinated and made available throughout the project
• Work has been divided in a fair way with extra attention paid to facilitating multi-tasking among group members – e.g. parts were broken up for analysis by system to create focus points for each member that can be carried through other parts of Gate
• Group members have honored intra-group due dates and stayed on schedule without exception

• Gate 4 has demanded more coordination and collaboration among members focusing on individual parts of the Gate. The division of the work among members has been characterized by overlap among the sections of the Gate, with members working on multiple sections. Thus, the number of large group meetings has decreased while the need for smaller meetings as two or three members working on the same section has increased. Members have reacted positively to this and have successfully coordinated small group efforts and meetings while maintaining contact at the group level via E-mail updates and brief in-person communications.

• Lay out guidelines for best practices and consistency in formatting group submissions of individual contributions to project to optimize both efficiency in uploading to the wiki page and appearance
• Compile and format group submissions into wiki form and create wiki page with appropriate flow and a single “voice”

• Group members continue to be guided by the very specific direction on how to submit their respective parts and how to send those submissions laid out in the last Gate. Any questions or requests for clarifications have been met with clear, complete responses.
• The wiki page continues to see consistent improvements in the use of media and its presentation

• Timing has become an issue as many members have had exams in the weeks since the last Gate was due, and communication has been sparse over the holiday. This has left relatively less time than was available in previous Gates for the Technical Expert to upload the wiki and reap the benefits of the group members’ constructive criticisms for improvement. To address this challenge, the Group has already started discussing the work to be done for the next Gate and is already looking toward improving this Gate and the previous Gates for the final project submission.

• Serve as a resource to other group members seeking more in-depth explanations of parts and part interactions
• Oversee the reassembly of the impact wrench, creating a detailed explanation of the process for both group members and the wiki page audience

• Technicians have been exceedingly available to group members to answer questions or provide insight outside of classroom and formal group meetings
• Technicians’ past experiences in working with machined items have proved invaluable to group’s ability to use the resources of the machine shop and its tools to reassemble the impact wrench

• The Technicians faced a few challenges in re-assembling the impact wrench but were able to overcome those challenges through their creative use of tools and by using their knowledge of how parts work and interact. The re-assembly process was recorded, and other challenges arose in editing the video and syncing the video with the sound, however, this challenge was resolved by reaching out to other group members with video editing software and skills.

Plunger

• Air acts as an ideal gas
• Temperature is constant
• Total volume inside the valve sleeve is constant
• The amount of air in the valve at any given point is constant

Ideal Gas Law:

PV=nRT (1)

where P is the pressure, V is the volume, n is the moles of gas, R is the gas constant and T is the temperature

Pressure Defined:

P=F/A (2)

where F is the normal force per unit area A, or the force applied perpendicular to the surface

After the trigger is engaged and air is allowed to flow through, the plunger alters the volume of the container through which the air may flow. Given all of the assumptions, PV = constant. Therefore, an increase in volume given by the plunger would yield a decrease in pressure proportional to the increase in volume and vice versa.

Since the pressure is defined as the force perpendicular to the surface area on which it is acting, the direction of the pressure is redirected when the plunger is rotated to the reverse position, thus applying force to rotate the fins in the opposite direction.

Back Plate and Switch

• The material of the spring is of uniform density and uniform spring constant
• There are no damping effects

Hooke’s Law:

F= -kx (3)

where F is the force applied by the spring, k is the spring constant which is characteristic of the spring and x is the displacement of the spring

The action of the spring pin locking into place in the grooves is defined by Hooke’s Law.

Fins

• Mass is constant
• Fins are uniform in shape and size and density is constant

Pressure Defined:

PA=F (2)

Impulse (a relationship defined by Newton’s Second Law):

J=∫Fdt = ∆p = m∆v (6a)

where J is an impulse, ∫_∆tFdt is the integral of the force F over an interval of time t, ∆p is the change in momentum, m is the mass, and ∆v is the change in velocity

The force exerted on the fins by the compressed air is a function of the pressure of the compressed air and the surface area of the fins. There is a direct relationship between the surface area of the fins and the force on the fins, and there is also a direct relationship between the pressure created by the air and the force exerted on the fins.

When air enters the rotor chamber it incurs a change in momentum caused by the contact with the initially stationary surface of the fins. This change in momentum is transferred to the fins as an impulse, which causes an increase in velocity of the fins and thus the rotation of the rotor.

Rotor

• Mass is constant
• The rotor is of uniform density and contact within individual grooves between the rotor surface and the fins is uniform
• The linear momentum of each of the fins is conserved and transferred to the rotor at a single point of contact that is uniform for each fin

Newton’s Second Law:

F=dp/dt=d(mv)/dt=m dv/dt=ma (6b)

where F is the force, and dp/dt is the rate of change of its linear momentum (p) with respect to time (t) and d(mv)/dt, the rate of change of the mass (m) times the velocity (v) with respect to time; m is brought out as a constant under the assumption of constant mass and dv/dt becomes acceleration, a

Torque as the Time Derivative of Angular Momentum:

τ=dL/dt=dr/dt×p+r×dp/dt=r×F (7)

where τ is torque, dL/dt is the rate of change of angular momentum with respect to time, dr/dt is the rate of change of the position vector (r) of the point relative to the center, and × indicates a cross product

The force of the fins against the surface of the grooves in the rotor causes the rotor to accelerate.

Due to the conservation of linear momentum, the linear momentum of the fins created by the impulse from the contact with the compressed air is transferred to the rotor at points of distance r from the rotor’s central axis. The change in linear momentum at these points on the rotor’s grooves, now a change in angular momentum given the cylindrical shape of the rotor, then creates torque. The torque spins the rotor which, in turn, spins the hammer.