Rolling Contact Joints in Robotics

Introduction

• Discussing rolling contact joints due to project requirements.
• Traditional ball bearings are too large for the current project.
• Aim to introduce these joints, which are not widely known.

Project Overview

• Building a bird-inspired robot that can hop around.
• Initial design used traditional ball bearings and carbon fiber rods.
• Encountered limitations with bearing size affecting design.

Rolling Contact Joint Design

• Composed of two halves with curved surfaces that roll against each other.
• Main components:
  • Rotational surfaces: Allow for smooth motion.
  • Outer walls: Provide rigidity to prevent out-of-plane movement.
• Unique properties allow for engineering specific surface shapes for desired movement characteristics.

Mechanical Design Details

• Joint resembles human and bird joints, featuring nonlinear motion.
• Two main surfaces:
  • Flat section transitioning into a gentle curve.
  • Steeper curve for additional rotational dynamics.

Connection Mechanism

• Uses a compliant mechanism (e.g., fishing line) to hold parts together.
• Fishing line type: Dyneema (ultra high molecular weight polyethylene).
• Threading technique:
  • Create loops to hold the joint together, using a figure-eight pattern.
  • Ensures robustness against unwanted movements.

Demonstration Steps

• Showed how to thread the fishing line through the joint.
• Completed joint allows for varied rotational movement based on internal design.
• Identified design flaw: joint rolls too far forward.

Key Benefits of Rolling Contact Joints

• Size: Can be made smaller than traditional ball bearings.
• Low friction: Surfaces rolling against each other minimize resistance.
• Aesthetics: The design can be visually appealing in robotics applications.

Current and Future Work

• Using rolling contact joints for small mechanisms impractical with ball bearings.
• Encouraged interest in these joints among hobbyists.
• Announcement of attendance at Open Sauce (June 14-16).
  • 150 creators and 500 exhibits expected.
• Future videos will cover project progress, including actuation mechanisms.

Conclusion

• Aim to spread awareness of rolling contact joints in robotics.
• Thanked viewers and mentioned future updates.