Note: This update replaces the belt-and-cylinder mechanism described in the Tropical Ring Update. This solution offers superior mechanical logic and omnidirectional efficiency.

The Problem with the Belts

The previous belt-and-cylinder design had a fundamental geometric weakness: in the equatorial zones, the contact angle was often ambiguous. It could not always guarantee a 100% grip when tensioned or a 100% release when idling. We needed a cleaner mechanical "binary"—either rolling or gripping.

The Solution: The "Pearl Necklace"

Imagine a high-tensile wire (Dyneema or Steel) strung with small, independent spheres—like a pearl necklace. Each sphere is free to rotate in any direction and makes direct contact with the ETFE envelope.

How it Works:

1. At Rest (Rolling): When the necklace is not under drive-tension, the pearls act as omnidirectional bearings. Any movement of the envelope beneath them causes the pearls to roll freely, allowing the balloon to shift or expand with minimal friction.
2. Under Tension (Gripping): When the operator pulls the necklace, the increased downward tension presses the pearls firmly against the ETFE. Because the pearls cannot "slide" along the wire itself, they lock and transmit the pulling force directly to the envelope, driving the rotation.

Material Specification: To optimize this, the "pearls" will feature a soft silicone or nitrile rubber coating. This ensures high static friction for the drive phase while maintaining smooth rolling during the idle phase.

The North Pole: Crossed PTFE Tubes

To handle the crossing of the two necklaces at the top of the sphere, we have implemented a Crossed-Tube Guide:

• Independent Movement: Two slightly curved tubes, oriented at 90°, act as a bridge.
• Ultra-Low Friction: The tubes are lined with PTFE (Polytetrafluoroethylene). This ensures that even when one necklace is under high tension, it can slide through the crossing point without interfering with the other axis.

The Tropical Ring: Passive Horizontal Stabilization

A common question regarding this harness is how the Tropical Ring stays level without motors. The answer is Symmetric Tension:

1. Gravity Alignment: The weight of the gondola pulls downward on the four lines anchored to the ring. This constant, symmetric tension naturally forces the ring into a horizontal plane.
2. Surface Stabilization: Because the ring is in continuous contact with the pressurized sphere, the envelope itself acts as a massive stabilizing jig. The ring cannot tilt significantly because it would have to "deform" the pressurized sphere to do so.

This creates a self-leveling architecture that requires zero electronics, zero sensors, and zero power to maintain orientation during flight.

Status

✅ Concept Finalised — Transitioning to prototype fabrication for friction-coefficient testing.

Call for Contributions:

We are currently seeking data or simulations regarding:

• Pearl Spacing: Optimal density to prevent ETFE "tenting."
• Wire Selection: Evaluating Dyneema vs. Stainless Steel for long-term creep resistance.
• Coating Durability: UV-resistant rubbers for high-altitude exposure.

"The crisis requires sharing, not secrecy."