10.2 Design Process
Iteration Documentation
The image above is a basic representation of our reverse double four-bar. This prototype helps us visualize the rough structure that we want our physical model to duplicate. In this model, we could roughly visualize the motion of the linkage system as well.
Initial Considerations From Prototype
Physical Stop for Repeatable Motion
The oversized gears relative to the range of motion present an opportunity to implement a physical stop at the top of the motion arc. This stop would act as a locking mechanism, ensuring consistent positioning and repeatability. By limiting the motion at a fixed point, it compensates for potential actuator input errors, enhancing precision without requiring complex recalibration.
Keyed Connections for Improved Stability
The over-reliance on glue in the prototype highlights a structural weakness that keyed connections could address. Replacing circular press-fit joints with keyed designs—featuring grooves or slots—would improve torque transfer between links, reducing slippage and increasing reliability. This shift could eliminate or significantly reduce glue usage, streamlining assembly and enhancing durability.
Relocating the Actuator for Mechanical Advantage
Positioning the actuator at the end of the first four-bar linkage, rather than at the base, would optimize the system’s mechanical advantage. This adjustment would allow the actuator to exert force more directly on the moving components, improving efficiency and reducing the energy required to initiate motion, ultimately boosting overall performance.
Gear Reduction for Enhanced Torque
Incorporating a gear reduction between the actuator and the motion links would increase torque transmission to the system. While this would come at the expense of speed, the trade-off would enhance the design’s carrying capacity, making it better suited for heavier loads and more demanding applications.
Scaling Down Horizontal Length
The extended horizontal span of the system appears to compromise its carrying capacity due to increased leverage and potential flexing. Scaling down the horizontal dimensions could stiffen the structure, improving load-bearing performance. (This aligns with basic mechanical principles, as shorter lever arms reduce bending stress, though testing would confirm the extent of the benefit.)
Counterweight for Balance
Introducing a counterweight would stabilize the system throughout its motion path. By offsetting the weight of the moving components, it would reduce strain on the actuator and improve energy efficiency, particularly during dynamic operation, leading to smoother and more controlled motion.
Refining the Grabber
The grabber, currently unfinished, requires focused development to ensure it meets functional requirements. Enhancements could include improved gripping strength, adaptability to various object shapes, or a more robust attachment mechanism, making it a fully integrated part of the system.
Video of Motion:
Bill of Materials for Prototype:
Actual Changes from Prototype:
Material and Structural Improvements
Material Change: Acrylic vs. Wood
The prototype’s wooden components were replaced with acrylic for aesthetics and durability.Use of Cut Metal Rods
To eliminate the prototype’s reliance on plastic pegs and glued connections, precision-cut metal rods were introduced. These rods provided stronger, more reliable connections between links, improving torque transmission and structural integrity between the plane. This addressed the initial criticism of poor connections by reducing adhesive use and increasing durability for repetitive use.Scaled-Down Horizontal Links
The horizontal links were shortened to reduce the system’s span and weight, as identified in the initial concerns. This adjustment minimized flexing of the links, stiffened the structure, and improved load-bearing capacity. The scaled-down links enhanced the system’s suitability for heavier loads.
Mechanical Enhancements
Smaller Gears for Easier Connection
The oversized gears in the prototype were replaced with smaller gears to simplify assembly and improve connection reliability. Smaller gears minimized alignment issues.Keyed Gears for Robust Connection
Keyed gears, featuring slots or grooves, were implemented to replace circular press-fit joints, addressing the prototype’s point of failure and glue dependency. With a keyed slot for the links, these gears ensured robust torque transfer, eliminated slippage, and enhanced reliability. This improvement also reduces assembly complexity, introducing a press-fit.Gear Reduction Implementation
A 12:1 spur gear reduction was added between the motor and motion links to increase torque, as proposed in the initial considerations. After testing sun and planet gears, spur gears were selected for their simplicity and effectiveness, significantly improving the system’s carrying capacity at the cost of speed, which was not a critical factor. While compound or planetary gears could offer further carrying capacity, the spur gear solution met design needs. There was a point of failure trying to connect the circular rod to a gear under high torque duress. Future iterations could incorporate a better keyed connection method to enhance gear stability.Base Modifications: Cuts for Counterweight and Motor Holder
The base was redesigned with cutouts to house connections for the counterweight and a motor holder. The counterweight, as suggested in the initial considerations, offsets the weight of moving components, reducing actuator strain and improving energy efficiency for smoother motion. The motor holder slot stabilized the actuator, minimizing vibrations.
Grabber and Pallet Refinement
Refined Grabber and Pallet Design
The undeveloped grabber was designed to emulate a forklift mechanism, paired with a custom-printed pallet for secure object handling. The pallet was tailored to complement the grabber, enabling consistent performance. The pallet could be further improved to better harness a specialty load.
Electronic Integration
Electronic Integration
Electronic components, including an Arduino and motor controller, were integrated to enable precise actuator control. This addition provided software-based motion limits, enhancing repeatability.