Phase 2
Claw Design
Embedded Files
Phase Overview
In this phase we will consider different designs for a fourbar claw mechanism. Design considerations, specifications, sketches, assumptions and reasoning are all included. The final goat reached in this phase is to successfully pickup the payload design created in the previous phase.
Design Constraints
Design Constraints
Prior to designing our grasping mechanism, we needed to take into account all the constraints given both explicitly through the deliverables and other underlying constraints that also needed to be considered. The main constraints that helped direct our designs in the right direction were:
The grasping mechanism must have at least one fourbar linkage in its design
The mechanism must be actuated by one 180-degree MG-996R servo
The servo motor cannot be directly attached to a link that contacts/grips the payload
The servo will interface with the provided Arduino shield. The Arduino must be programmed that one potentiometer closes and opens your claw
Preferably a more universal design which can grasp not only our payload, but other teams
The mechanism must mount to the test rig provided which has two #8 screw holes 1 inch apart, vertically
The payload may be picked up anywhere along the mid-line of the test rig.
Most pieces should be made of 1/4" plywood that can be cut on the laser cutter.
Preferences that were taken into account but did not ultimately affect the designs as much were:
Design should be relatively easy to make
Preferably not include half or full sliders
Sketch Design 1
Pros:
Works with fully rotating servo
Arms work simultaneously
Cons:
Use of 2 half sliders could make it difficult to manufacture
Sketch Design 2
Pros:
Symmetric design
Arms work simultaneously
Cons:
Requires 2 servo motors
Only allowed 1 servo
Sketch Design 3
Pros:
Simple design
Claws are always symmetric
1 degree of freedom
Cons:
Ground pin location is precise
Sketch Design 4
Pros:
Works with a fully rotating servo
Arms work simultaneously
1 degree of freedom
Cons:
Use of half slider could make it difficult to manufacture
Degrees of Freedom Analysis of Design #3
Why We Chose Design #3
Why We Chose Design #3
Out of the 4 designs, this one is easily the simplest and the most realistic for us to manufacture. It requires only 1 servo motor, doesn't require any additional sliders and only has 5 links.
The degree of freedom (DOF) analysis for this design is satisfactory, there is only one DOF for the entire linkage. We speculate the one DOF is the angle of the link that directly connects to the servo motor (or the crank).
One of the constraints particular to this design is that the links that we manufacture cannot be too large. Larger links would prevent proper movement between links (2), (3), and (4), and therefore would prevent links (1) and (5) from opening fully. We overcame this design hurdle by decreasing the overall thickness of all the links, this ensured that the mechanism could open fully to accommodate all payloads.
Graphical Linkage Synthesis (GLS)
Graphical Linkage Synthesis (GLS)
Each button is linked to a more detailed image/file on Google Drive.
The open position for our claw will accommodate even the largest payload sizes.
The closed position of our claw design may accommodate smaller payloads.
Future design considerations include what geometry the claw will use to grip our payload.
Located above is the GLS which displays all the possible obstructions in addition to all the other details provided in previous GLS photographs.
SolidWorks GLS File
SolidWorks GLS File
The following button/image will link to the SLDDRW file that can be downloaded from Google Drive. When accessed using SolidWorks, the movement of our linkage can be clearly demonstrated
Using PhotoWorks, we were able to create photo-realistic renderings of both the open and closed positions of our claw mechanism which can be compared to the real claw we constructed in class. The comparisons can be viewed below.
"Open" Position of Rendering
"Open" Position of Rendering
Modeled Using PhotoWorks
"Closed" Position of Rendering
"Closed" Position of Rendering
Modeled Using Photoworks
In-Person Comparison Photo
In-Person Comparison Photo
Taken in Class After Testing
Reflection
Reflection
The overall design process went quite smoothly with only minor incidents that were efficiently resolved by various members of the team. The final result came out quite similarly to the original concept design despite some adjustments to either fit criteria better or to just work better. The final claw design was able to successfully pick up every payload design in the entire class of several groups. One possible adjustment we may consider changing in the event of another claw being manufactured would be a redesign of the contact points for the claw so that there is a higher surface area which is in contact with the payloads.
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