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The Life-sized Human-interaction Robot
Purpose
The client's vision for a soft-robot replica of Baymax presented an exciting challenge for our team, with a particular focus on the design of the robot's arm from shoulder to wrist. The primary goal was clear: create a robot capable of meaningful interactions—fist bump, high-five, and hug—while embodying the soft and friendly aesthetic synonymous with Baymax. Additionally, the design needed to balance functionality with foldability for convenient storage.
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I was responsible for designing the elbow mechanism. Beyond meeting functional requirements, my task was to ensure the design adhered to stringent safety protocols, all while preserving the iconic appearance that defines Baymax.
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Critical components, such as the shoulder joint (yellow), elbow joint (teal), structural members (black), and inflatables (white), were systematically analyzed throughout the design process.
Process
The project commenced with a thorough analysis of client requirements, emphasizing the need for a soft, replicable Baymax arm capable of dynamic gestures. My initial design incorporated a cable-driven universal joint. However, after conducting simulations and hand calculations, it became evident that this approach would compromise the proportions of Baymax.
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Undeterred, I iterated on the design, introducing a belt-driven differential joint. This modification significantly improved strength and facilitated the mounting of motors closer to the shoulder, streamlining forearm actuation.
Design Iterations
Cable-driven Universal Joint
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Overview: The initial design revolved around a cable-driven universal joint at the elbow. This joint featured three wires, strategically spaced at 120 degrees, passing through inserts in the upper arm, guided by a carbon fiber core. The universal joint comprised a yoke (blue) connected to the forearm, another yoke (white) linked to the upper arm, and a center block (teal) secured by threaded screws (pink). This configuration allowed free rotation, facilitating natural and expressive movements.
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Functionality: The hollow core of both the center block and yokes served as the path for hand cables. The arm movement was controlled by three cables: the top cable controlled vertical motion, while the two side cables managed horizontal motion. Linear actuators in the upper arm extended or contracted these cables, manipulating the arm's position. In its resting state, with the top cable fully extended and side cables in the middle, the arm remained straight. Retracting the top cable simulated a vertical raise at the elbow, mimicking a high five. Manipulating the side cables allowed the arm to bend inward, allowing Baymax to give a warm and comforting hug.
CAD Model
Belt Driven Differential
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Overview: The second iteration introduced a Belt Driven Differential system. This design leveraged two stepper motors, 2 V-belts, 3 bevel gears, and a high load capacity bearing to provide the elbow with 2 Degrees of Freedom (DOF). Inspired by the differential system employed in the open-source robotic arm, Thor, this mechanism demonstrated enhanced strength and efficiency.
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Functionality: The coordination of two stepper motors dictated the arm's movement. When both motors rotated in the same direction, the arm lifted vertically, while opposite rotations resulted in rotation about the y-axis. This design was chosen for its' improved strength and smoother articulation. Given the strength and durablity of the design during simulations, it was clear this design offered more precise and reliable execution of gestures.
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The two design iterations were shaped by a methodical approach, utilizing simulation testing in Fusion 360 and hand calculations to anticipate and address potential issues before implementation. Informed by this data, I researched proven alternatives, adapting them to align with the project's unique challenges. This focused process, rooted in practical problem-solving, ensured that the final Baymax arm designs were both robust and tailored to meet functional requirements.
Final Design
Carbon Fiber Inner Core (Black):
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The arm features two carbon fiber inner core members, providing structural support and rigidity.
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This choice ensures a lightweight yet robust foundation for the arm's movements.
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Belt-driven Differential Joint (Teal):
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Facilities smooth and natural movement of the arm.
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Designed for reliability and precision control.
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Inflatable Components (White):
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Surrounding the inner core are three inflatables, each contributing to the arm's flexibility and user safety.
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A specific design with six long tube-like structures optimizes foldability, motion range, and coverage.
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Polyethylene Cover (Not Pictured):
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A lightly pressurized polyethylene cover (omitted from images, for clarity) envelops the entire structure, providing the appearance of a continuous balloon.
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This design choice not only contributes to the arm's soft and friendly aesthetic but also facilitates easy storage with its foldable nature.
Impact
The culmination of the Baymax arm project embodies strategic engineering decisions. Such choices are evident in the design of the belt-driven differential joint. This design, validated through hand calculations, simulation testing in Fusion 360, and practical considerations, ensures both strength and efficiency. The strategic placement of motors closer to the shoulder simplified actuation and reduced the torque requirement of the shoulder motors.
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Furthermore, I identified potential challenges early on, ensuring a robust final product. The intentional design extends beyond technical merits, incorporating user-centric considerations. The elbow design allows for the strategic routing of cables from hand to shoulder, the soft exterior inflatables provide a barrier between the user and the mechanical components, and the carbon fiber core provides rigidity and strength for the arm that allows users to feel the physical feedback of the gestures.
These choices enhanced both the functionality and user experience.
In essence, the results of the Baymax arm highlight the practical impact of thoughtful design choices. This journey of learning and application underscored the importance of simulation and calculation-based validation and user-centric design.