5.1 - Initial Proposal
G.O.A.T. (Grip-Oriented Ascension Tech)
Introduction
Our team was inspired for this project by a video of a university competition where teams designed a robot to traverse a horizontally suspended rope. We also found a video of a small Lego robot that climbs up a rope through elastic bands and human actuation of the rope. We wanted to adapt this idea so the robot is driven by a motor and can climb the rope without human assistance. This idea is useful because it could be adapted to transport materials vertically, which could be useful for industries like mining and construction.
Problem Statement
Our problem is creating a mechanism with a complex position profile to allow our robot to traverse a rope that is suspended vertically. The legs of the robot need to be in coordination with each other for the robot to maintain its weight distribution. Controlled forces need to be applied to the rope to ensure clamping and climbing up the rope periodically using a system of intermittent motion. Simple joints will not work for this system due to the oscillation of the rope and the need for balance.
Mechanism
To solve this problem, we propose using a 4-bar linkage, like the one pictured above. This linkage will be designed such that the geometry of link 4 allows for the rope to slide through easily when the link moves upward, but holds the rope tightly when moving downward to allow the device to climb the rope. We also plan to use a secondary linkage, powered by the same actuator, that clamps the rope to link 1 while link 4 moves up and then releases when link 4 moves down so that link 1 can slide up the rope. This secondary linkage will use a Geneva mechanism to create dwells that alternatively clamp and release the rope.
Scope
For the scope of this project, we plan for our final product to be a robot that can independently climb up a vertical rope, without any assistance from human actuation. For our fabrication, we will need to perform positional analysis to determine how the limbs of the robot will reach up the rope to propel the mechanism. We will also need to perform force analysis to ensure the rope remains taught as the mechanism changes position and that there is sufficient friction between the pins on links 1 and 4 and the rope to keep the robot from slipping. Some additional steps that we will need to consider are methods to minimize the number of actuators necessary for this design and implementing programming controls for the speed and distance of the climb.
Preliminary Design
For the preliminary design, we’ve decided to slightly modify the 4-bar linkage described in the mechanism section to create a crank-rocker mechanism so that we can use a continuous actuator, rather than one which requires positional inputs to simplify the robot’s programming. A kinematic diagram for the proposed mechanism is shown below:
Kinematic Diagram:
Gruebler’s Equation:
Number of Links: 4
Number of 1 DOF Joints: 4
Number of 2 DOF Joints: 0
M = 3 (4 - 1) - 2 (4) - 0 = 1 DOF
Grashof Condition:
L1 = 64.0312 mm
L2 = 35 mm
L3 = 55 mm
L4 = 55 mm
S + L < P + Q
35 + 64.0312 = 99.031
55 + 55 = 110
99.031 < 110
Based on the Grashof Equation, our preliminary design is a Type I linkage, so link 2 will be able to rotate fully through 360 degrees.
Position Profile of Point P:
This a plot of the y-position vs. the x-position for Point P on Link 4 for all positions of Link 2 0-360 degrees. Point P will make one back-and-forth motion of this curve every time L2 rotates fully.
