5.2 - Design Process

Physical Prototype

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Prototype of Rope Climbing Mechanism that is hand-powered and requires tension from below

This version of the prototype was the product of phase 3 of the prototype iteration and achieves the desired complex motion profile by climbing up the rope. The scope for this prototype was to construct a robot that is able to climb up the rope which we achieved. However, it is currently manually powered and requires assistance providing tension to the rope. The major next steps to the final product are incorporating a motor to drive the mechanism on its own and a clamping mechanism to provide tension to the rope. We also have additional optimizations we would like to make based on what we learned from testing this prototype. Now that we know our basic mechanism can successfully climb up the rope, we can work towards to allowing it to do so unassisted.

Path to Final Design

1. Reduce the overall size of the robot and link lengths to reduce the weight

2. Add another point of contact with the rope at the bottom of link 1 to provide more stability as it climbs up the rope

3. Dwelling mechanism (Phase 4 of Prototype on Iteration Documentation) to clamp and release the rope and take the place of our manually-provided tension

4. Incorporate a motor to drive the rotation of link 2

5. Allow for controlling whether the robot climbs or not with a switch

Iteration Documentation

Phase 1: Understanding the Motion

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Popsicle Stick Prototype

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Popsicle Stick Prototype in Motion

The first version of the prototype was built with Popsicle sticks and a rubber band to understand the intended motion profile of the final product. We wanted to achieve a mechanism capable of climbing up the rope with the assistance of tension on the rope that would be replaced by a clamping mechanism in the final product. Things we continued from this version of the prototype to the next iteration include how the rope was threaded between the links and the basic movement of stretching the links apart to inch up the rope with an in and out motion. Lessons we learned from this version include considering a way to maintain stability as it is suspended on the rope and the importance of considering the spacing and tension between the mechanism and the rope which was getting caught in this version.

Phase 2: Planing Linkages

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Phase 2: Motion of linkages and link lengths

The next iteration of the prototype was intended to the plan the basic linkages and lengths as well as where they would connect. It was modeled off of the basic movement above, but incorporated a crank-rocker mechanism to actuate link 2 to allow it to be driven by the spin of a motor. From this phase we understood more of the physical constraints of the link lengths and the best way to drive the mechanism. The plan for the next phase was to create a model that could be physically implemented as our prototype.

Phase 3: Rope-Attached Hand-Powered 4-Bar Linkage

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Phase 3 Prototype: Rope-Attached hand-powered 4-bar mechanism with linkages

This phase of the prototype development had the goal of creating a model that could be translated into a physical prototype that we can test with the rope. At this stage our planned scope was to develop a physical model that could climb up the rope while being hand-powered. The intention was to determine if our mechanism could achieve the correct range of motion and apply the necessary forces to climb up the rope. Key takeaways we gained with this prototype included the importance of carefully balancing the friction between the rope and the links as well as the need to for strong tension in the rope. After constructing the physical prototype of this model (which is able to climb up the rope with hand-actuation and assistance providing tension on the rope), we fine-tuned the friction and rope tension, and created a plan for a self-actuating robot.

Phase 4: Dwelling Mechanism

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Phase 4 Prototype: Hand-powered 4-bar linkage with secondary dwelling linkage

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Phase 4 Prototype: Video showing the motion of both the clamping and climbing linkages

The next phase of the prototyping process focused on integrating a second linkage to clamp and release the rope on the upper portion of Link 1. This will be achieved using a cam-follower mechanism. The cam is placed on the same axle as the joint between Links 1 and 2 so that it rotates at the same rate as Link 2. The cam is two-sided so that follower link retracts without needing a spring. The follower link will be constrained by a set of bearings (not shown) that constrain its motion to be parallel to the horizontal portion of Link 1 so that the follower link moves left and right to clamp and release the rope against a fixed pin. Additionally, since the cam must be positioned close to the clamping point, this design was inverted so that the joint between Links 1 and 2 sits above the joint between Links 1 and 4 rather than below as in the phase 3 prototype.

Draft Bill of Materials