10 - Initial Project Proposal

Problem Statement

In the world of kinetic art, the Strandbeest, crafted by Dutch artist Theo Jansen, stands out as a wind-powered sculpture with intricate leg mechanisms that gracefully traverse sandy terrains. However, its design is primarily suited for flat landscapes. With the diverse topography of urban environments, particularly stairs, there's a compelling challenge to evolve the Strandbeest's mechanical design for multi-terrain adaptability. This adaptation not only pushes kinetic art boundaries but also offers practical applications, potentially guiding robotic designs for varied terrains. Our project's proposal aims to address this challenge head-on by developing a Strandbeest capable of walking on flat ground and seamlessly transitioning to ascending stairs.

Complexities Involved

Creating a four-legged Strandbeest mechanism capable of traversing both flat ground and stairs presents multifaceted challenges. Here are the complexities involved in addressing this problem:

• Dynamic Stability: Unlike flat ground, stairs introduce varying levels of elevation. Ensuring the Strandbeest maintains its balance during ascent and descent is critical. This involves optimizing the center of gravity and ensuring that at any given point during its movement, the Strandbeest remains stable.
• Adaptive Leg Mechanism: The leg design must be adaptable. On flat ground, the legs need a certain stride length and movement pattern. For stairs, the legs need to have a different range of motion, allowing for higher steps and ensuring that the body clears each stair level.
• Kinetic Synchronization: With four legs, coordinating their movements to ensure that there's always a stable point of contact is challenging. This becomes even more intricate when considering stair traversal, where miscoordination can lead to tipping or stumbling.
• Electrical Component Weight: Adding components like motors and batteries increases the Strandbeest's weight. This stresses joints, potentially hastening wear or causing structural issues. Moreover, the added weight can shift its center of gravity, affecting stability and possibly necessitating design changes for balance.
• Single Motor Integration: Utilizing a single motor to drive the entire mechanism amplifies several challenges:
  • Torque: A lone motor struggles to distribute torque across four legs, especially on stairs, making synchronized movement intricate.
  • Mechanical Design: Powering all legs requires intricate gear, linkage, or belt systems, heightening design complexity and failure risks.
  • Synchronization: Keeping all legs coordinated with one power source is challenging, with small discrepancies potentially causing inefficiencies or Strandbeest malfunctions.

Using a simple joint in a complex mechanism like a four-legged Strandbeest, especially one designed to traverse both flat ground and stairs, presents several challenges and limitations:

• Limited Range of Motion: Simple joints typically offer movement in a single plane or direction. For a Strandbeest, which requires intricate leg movements to adapt to varying terrains, such limited motion can be restrictive.
• Lack of Adaptability: A Strandbeest needs to adjust its gait and movement patterns based on the terrain. Simple joints lack the adaptability to make these nuanced adjustments, which can result in inefficient movement or difficulty in traversing certain terrains.
• Reduced Stability: The stability of the Strandbeest, particularly when transitioning between different terrains, relies on the coordinated movement of its legs. Simple joints might not provide the necessary flexibility or synchronization, leading to potential balance issues.

Description of Proposed Mechanism

The Jansen linkage mechanism is a one-degree-of-freedom planar linkage consisting of eight links and seven revolute joints, as shown in Figure 1. Jansen linkage mechanisms are bioinspired and mimic the gait cycles of their biological counterparts, such as the "Strandbeest." They can create a walking motion due to the specific arrangements of the linkages and joints. The crank (m) serves as the input mechanism that drives the motion of the entire linkage and is capable of a full revolution. The rocker arms (J, K) connected to the crank move back and forth as the crank completes a revolution. The back-and-forth motion of the rocker arms is then transmitted to the transmission links (E, F). Finally, the transmission links are connected to the walking leg mechanism (H, I). As the transmission links move back and forth, they drive the walking leg mechanism, causing it to lift off the ground and move forward.

The overarching goal of this project is to engineer a robot mechanism that takes advantage of the specific motion profile of the Jansen linkage mechanism, enabling it to navigate complex terrains, such as stairs. The geometry of the linkages can be adjusted to fit the specific motion requirements of a desired stair or terrain, as shown in Figure 2. For this project, we plan to use at least four Jansen mechanism parts in the design of our robot's legs to ensure dynamic stability. Since our mechanism is a one-degree-of-freedom linkage, we must ensure that all the Jansen mechanisms in our robot share motion, either through gear or belt systems. After building our mechanism, we will thoroughly test it to ensure that all the components work together to produce the desired motion and minimize wear and tear.

The Jansen linkage mechanism can create a captivating and almost lifelike walking motion, setting it apart from motions created using simple joints. In this project, we aim to create a mechanism that not only functions well in navigating complex terrain but also possesses artistic and aesthetic value. This project allows us to combine engineering and art to create a robot mechanism that is both pleasing and awe-inspiring to observers.

Proposed Scope of the Project

The conceptual design and physical application of the Strandbeest have been explored for several decades. The Jansen linkage utilizes a very unique linkage system and provides a very similar motion profile to that of a walking person. However, the challenge lies within the ability to leverage the linkage to modify motion profiles to adapt while the Strandbeest is walking. This project aims to develop and model a fully functional Strandbeest capable of traversing uneven terrain that is within reasonable scale with respect to the size of the model. In order to achieve this goal, the first phase will entail developing a working prototype of the target motion profile capable of walking across flat terrain. Then the following model will aim to integrate the initial model with the ability to climb a set of stairs or obstacles.

The nature of this challenge requires a significant amount of analysis prior to fabrication due to the complexity of the linkages involved. An in-depth motion analysis needs to be conducted to optimize the paths for the intended terrains the model is designed for. This phase will focus on completing CAD models of the linkages and then a motion study of the model and its sub-assemblies. Then the model will be validated using FEA analysis to ensure a durable prototype. Once this phase is completed, the project will move into the fabrication stage.

Fabrication is a significant challenge for this project as the linkages are very complicated and will need to be constructed with precision to ensure a smooth operation. The model is currently intended to be fabricated using 3D printers, hardware fasteners, and laser-cut acrylic. This will be the most anticipated part of the project as all of the planning and careful execution will lead to a cohesive design and cross between engineering and art.

Currently, our team members are all involved in robotics-based projects and this project aims to help broaden our understanding of complex linkages and leveraging mechanical design to simplify motion. This project will also help our team members create an engineering model that is visually appealing and interesting.

Preliminary Design Ideas

Below is a preliminary idea of the motion profile of the Strandbeest's leg on a flat terrain. The measurements outlined for the linkages are not the actual measurements to be used.

Figure 1: Motion profile of regular Jansen Mechanism generated using MotionGen 

Below is a preliminary idea of the motion profile of the Strandbeest's leg during stair ascent.

Figure 2: Proposed preliminary design of the Jansen linkage to ascend stairs

References: (1) Shunsuke Nansai.; et al.. Speed Control of Jansen Linkage Mechanism for Exquisite Tasks (2015)