Phase 2: Grasping Mechanism

Objective Statement

The primary goal of Phase 2 of the project is to design a fourbar linkage that is controlled by a servomotor, and connects with an arm (coupler) which will create the grasping mechanism of the mechanical arm. The purpose of this grasping mechanism is to grip and hold the all of the payloads previously designed during Phase 1.

Design Constraints

Explicit Constraints:

• At least one fourbar linkage has to be present in this grasping mechanism

• Has to have 2 mounting holes that are 1 inch apart and sized appropriately for #8 screws

• Link attached to servo cannot directly contact payload

• Only one servo motor

• The grasping mechanism has to interface with our payload design from Phase 1

• 1/4" Plywood material (Pine)

• Cannot utilize gears

• Servo can only move 180 degrees

Implicit Constraints:

• The grasping mechanism must integrate with all payloads

Team Imposed Constraints:

• Create a claw with the least amount of links possible for simplicity

• Develop a compact design that is lightweight

• Shape the coupler so it can grasp any payload

Design Considerations

Design #1:

Our Thought process:

We did like this design because the center of mass would be supported by the claw and the overhead grab rather than be grabbing the payload from the sides. However, the ends of the claw would prevent us from having a proper surface area contact with other pay loads that have flat sides. We were also concerned that the crank and rocker would come in contact with one another and interfere or prohibit movement. The final point of concern was the large horizontal profile that the claw would have to sufficiently hold the servo when its on its side.

Design #2:

Our Thought Process:

We chose this design because the servo would be directly over the payload and under where the claw would attach to the arms, properly supporting the center of mass. The placement of the crank and rocker ensured no interference and the static flat end along with the slightly curved other end would allow for maximum surface area contact. And overall we liked the simple design.

Design #3:

Our Thought Process:

Another simple linkage where the right side is fixed. This design is really a combination of 1 and 2 in that the servo is mounted on its side like design 1 and the coupler has the same shape as design 2. We decided against moving forward with this design because we thought that mounting the servo horizontally would make our claw too bulky in size and might interfere with the placement of the rocker.

Graphical Linkage Synthesis (GLS)

Narrative:

When designing the claw in Solidworks special consideration had to be given when deciding on the length of each link. The length and placement of each link was carefully chosen to avoid interference and to allow for movement between open and closed positions. Creating ample space for this model servo was also considered in the design phase of the claw. Design considerations were also made for the size and shape of the coupler so that it could effectively interface with any other team's payload design.

GLS Screenshots:

GLS Download:

Final Model: