10 - Stair-Ascending Strandbeest

Summary

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. Below is a short video demonstrating our project and the design process.

What is a Strandbeest?

The term "Strandbeest" translates to "beach animal" in Dutch. These sculptures are made from lightweight materials such as plastic tubing and are powered by the wind. They are designed to walk on beaches, driven by the wind's force, and feature a complex system of joints that allow them to move in a lifelike manner. The Jansen mechanism, also known as the Jansen linkage, is a mechanical linkage system that Theo Jansen developed for his Strandbeest creations. The Jansen linkage mechanism is a one-degree-of-freedom planar linkage consisting of eight links and seven revolute joints. Jansen linkage mechanisms are bioinspired and mimic the gait cycles of their biological counterparts, such as the "Strandbeest". The Jansen mechanism is crucial to the walking motion of the Strandbeest, allowing it to harness wind energy and convert it into a walking motion. The key features of the Jansen mechanism include a series of crankshafts, rods, and articulated joints that work together to create a walking motion. Each leg of the Strandbeest consists of multiple segments, and the joints are designed to move in a way that imitates the leg movement of animals.  When the wind exerts force on the sail or wings of the Strandbeest, it drives the crankshafts, causing the legs to move in a coordinated manner and propelling the sculpture forward (Figure 1).

Figure 1: Example of a Jansen mechanism and large-scale "Strandbeest" (Credits: Theo Jansen, Strandbeest.com)

Proposed Design and Modifications

Our project proposal is focused on addressing the challenges of a classical Strandbeest mechanism by developing a modified Strandbeest (Figure 2). This evolved design would maintain its ability to walk on flat surfaces while also gaining the capability to ascend stairs efficiently. To traverse flat surfaces and ascend stairs, our design utilizes a five-legged Strandbeest with the use of the Jansen mechanism. Four regular Jansen Mechanism legs and an out-of-phased leg situated on the anterior end of the Strandbeest enable it to climb stairs. The fifth, out-of-phase leg has a modified linkage length to have a higher step height to enable stair climbing.

Figure 2: CAD of a modified Strandbeest designed for traversing flat surfaces and ascending stairs 

Figures 3 and 4 below show the kinematic analyses of the regular Jansen mechanism leg and the modified leg with a higher step height. For the modified leg, the distalmost anterior link is designed to be half the length of the regular Jansen mechanism to achieve the motion profile needed for a higher step height.

Figure 3: Motion profile of regular Jansen Mechanism generated using MotionGen

Figure 4: Motion profile of modified Jansen Mechanism generated using MotionGen

Content

1. Initial Project Proposal
2. Kinematic Analysis
3. First Prototype
4. Final Prototype
5. Conclusion