02 - Compliant Joint Walking Mechanism with Nitinol Actuator Drive

Our project is a compliant mechanism powered by a nitinol actuator to provide a new, more suitable design for lunar exploration, as it would have a greater resistance to mechanical wear, less mass, higher energy efficiency, and increased simplicity, relative to current designs. Our mechanism consisted of two main alterations: 1. compliant joints and 2. power input from a nitinol actuator.

The Team:

The members of this project consisted of Evan Blount, Joshua Cheung, and George Coutoumanos, three undergraduate students at the University of Texas at Austin. This project was completed in the Fall semester of 2023.

Summary Videos:

For Gen Z, Gen Alpha, and other TikTok enjoyers: YouTube Link

For everyone else: YouTube Link

Official Summary Video:

For another QUICK overview of our project check out this Poster

What are compliant joints:

A compliant joint is a mechanical connection between two components designed to allow flexibility and deformation within certain limits, essentially acting as a rigid joint without moving/mechanical parts.

The advantage of compliant joints for lunar exploration:

Compliant joints prove to be highly advantageous for lunar exploration due to their longevity and suitability for the challenging lunar environment. These mechanisms offer simplicity by having fewer parts than their traditional rotational counterparts, reducing complexity for assembly and total points of failure. Their lack of mechanical parts avoid the detrimental wear provided by the moon’s abrasive lunar dust. Additionally, compliant joints are considerably lighter than ball bearings or pin joints, ultimately reducing the total mass of the mechanism. Having a lightweight design is crucial for reducing overall spacecraft weight, addressing the cost premium associated with every kilogram of payload transported to the Moon (to get 1kg of payload to the moon is estimated to be $1.2 million with current earth to moon transportation methods). This weight reduction not only contributes to launch cost efficiency but also facilitates enhanced maneuverability during lunar missions.

What is a nitinol actuator:

A Nitinol actuator is a type of actuator that utilizes Nitinol, a shape memory alloy, as the driving element. Nitinol changes shape in response to temperature variations or mechanical forces (temperature variations cause a much stronger response than mechanical forces with nitinol)

How nitinol was used:

We exploited nitinol’s properties, listed in the previous section, to create a driving force for our mechanism, by using two nitinol actuators as follows: (1) at a starting position, the left actuator is at equilibrium and the right actuator is deformed, by heating up the deformed actuator, with an electrical current, an input force is created as the nitinol wants to move to its equilibrium position; (2) while it travels to its equilibrium position, the other nitinol actuator begins to deform; (3) once the actuator reaches equilibrium and the other is fully deformed, the electrical current switches to the newly deformed actuator; (4) step 1 is repeated, but the left actuator is deformed with a supplied current and the right at equilibrium with no current; the cycle repeats steps 1-4. With this concept (a cycle of force in the direction of one actuator to the next) we could create a motion profile in the shape of an ellipse. This elliptical motion is the input for the rest of our mechanism.

blue = no current

red = supplied current

figures

1.) 2.)

3.) 4.)

The advantage of a nitinol actuator for lunar exploration:

Powering our mechanism with a nitinol actuator provides three key advantages compared to standard motors. Firstly, nitinol is particularly powerful, especially relative to its mass, meaning the mechanism will be capable of moving objects other than just itself around the moon, a key factor for a robot's effectiveness in lunar missions. The second advantage: it is much lighter than traditional motors, which, again, addresses the cost premium for transportation to the moon. Lastly, nitinol also avoids mechanical parts, removing wear from the lunar environment.

Although improvements such as effective traversal of rocky terrain, stability and closed loop cycles (sensor feedback controls) need to be implemented, this mechanism acted as a solid proof of concept for the feasibility and suitability of a compliant mechanism paired with a nitinol actuator and could successfully be implemented as the means of mobility for a lunar rover to solve 3 main issues with lunar exploration: mechanical wear, mass, and efficiency.

Table of Contents:

Next Section: Initial Project Proposal