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Objective:
Design a graphical linkage simulation for our four-bar claw to pick up the payload
Design Constraints:
Mechanism must be actuated by one 180-degree MG-996R servo
Mechanism must mount to the test rig with two #8 screw holes spaced 1 inch apart, vertically
Materials include: 1/4" plywood, wood glue
Must be able to pick and transport payload made in Phase 1
3 weeks to finish Phase 2
Design Considerations:
Design #1
Design #1
Pros: It is a simple design with easy movement.
Cons: The rocker ends up hitting the motor, making this design not suitable for the project. Anchor holes are too close together.
Design #2
Design #2
Pros: Fixes the complication with Design 1 and still allows easy movement.
Cons: There is only one arm and it is less centered. Anchor holes are too close together.
Design #3
Design #3
Pros: Fixes the dimensions of holes to attach to testing rig. Creates more space for the Servo. Flat pieces are attached to the end of the claw to create more surface area to grab onto payload
Final Design Chosen was #3 as the design creates the best clearance of the servo while maintaining the four-bar mechanism. Claw can easily grab onto the payload on flat surfaces onto the center of the payload.
Degrees of Freedom Analysis for Design #3:
4 Linkages; 4 Pin Joints; 0 Full Slider Joints; 0 Half Slider Joints
DOF = 3( L - 1 ) - 2( Jp + Jfs ) - Jhs
DOF = 3 (4 - 1) - 2 ( 4 + 0 ) - 0 = 1 --> Mechanism
Graphical Linkage Synthesis (GLS):
Design chosen utilized a four-bar mechanism to create claw. Curved coupler shape was chosen to ensure clearance of servo. The placement of the servo in the horizontal position allows the claw to be shortened to increase rigidity in the mechanism.
Design Renderings:
Closed Position
Closed Position
Open Position
Open Position
Comparison Photo:
Reflection:
The grasping mechanism performed as we predicted. We were able to pick up all the class payloads as intended. Since our mechanism worked properly, no changes are needed at the moment. Changes may arise when mechanical arm is implemented. Claw presents slight wobbliness at the connection between testing rig and claw but could be improved by adding washers.
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