Phase II

Explicit Constraints

The grasping mechanism needs to contain a fourbar linkage.
The mechanism must be actuated by a 180 degree servo motor that isn't connected to any link that makes contact with payload.
The mechanism must be compatible with the predesigned testing rig, and be able to pick up the payload at some point on the midline of the testing rig.
The parts of the mechanism should be primarily made of 1/4 inch plywood.

Implicit Constraints

The grasping mechanism needs to incorporate a "catching" component in its design if the payload slips during any time of transport.
Keep between servo motor travel between 0º to 170º (it is unlikely that the servo will be able to rotate the horn to the full 180º due to motor design limitation).
The design should be as minimal as possible, to avoid adding excess weight.

Pros: Center of gravity should be close to the midpoint of claw, avoiding any issues with weight distribution on the arm

Cons: Coupler design can be improved, overall linkage placement is awkward

Pros: Rubberized grips on bottom for stabilizing grab, stable design for bigger payloads, bent arms to allow a wider payload

Cons: Might be too heavy to carry, hard to follow the design, will be harder to build than more simple design

Pros: Simple design, makes usage of even weight distrubution, designed as to not crush payload

Cons: Difficult to place servo motor, not an anti-slip design for our specific payload, angle for bottom "teeth" is difficult to calculate, hard to incorporate this design into our specific project

Pros: Angled parts avoid unwanted contact with the payload, grip points allow use of the payloads anti slip feature, and a large space to mount the motor

Cons: Forward set grip could make the mechanism front heavy, and the grip points could either come unaligned and spin the payload or get caught on the payload.

Design Considerations:

When we chose our final design for grasping mechanism, our group blended ideas from Josh's ground link and Aaron's coupler/rocker/crank design. The major discussion points/ideas that went into the design of the final grasping mechanism are as follows:

Use Josh's positioning of the servo motor and crank to the base as it allows more room for the servo motor to be mounted, and keeps the payload better centered underneath the arm while being lifted.
Incorporate Aaron's coupler with enlarged contact point to maximize surface area to payload and make use of the anti-slip edges that were designed into our payload.

Degrees of Freedom Analysis:

3(linkages - 1) - 2(pins - full sliders) - half sliders

3(4 - 1) - 2(4 + 0) = 1 DOF

Final Decision

Open and Closed Positions of the GLS

The screenshot our Graphical Linkage Synthesis above shows the positioning of our grasping mechanism in both its open closed position (position one) and its open position (position two). This design is compromised of a mixture of ideas taken from both Aaron and Josh's brainstorm ideas which were then refined to remove unwanted weight, sharp corners, and allow sufficient room for the servo motor to be mounted. As can be seen on the our basic representation of the coupler we used a rectangular grip point with right angled corners. This decision was made in order to take full advantage of the anti-slip edge cut into the sides of our payload.

Phase II

Degrees of Freedom Analysis:

Final Decision

Open and Closed Positions of the GLS

Open and Closed Positions of the Assembly

The Grasping Mechanism in Action