Manufacturability is the driver of the substantial changes to the 2009 drifter. Instead of a two-hull design, the sensors are now directly exposed to the external environment. Our redesigned hull combines off-the-shelf components with a machined plastic enclosure. The propulsion scheme still uses two propellers in a differential drive configuration, but external motor pods made the design easier to assemble and repair. A new buoyancy control system opens up new possibilities for sensing missions, by allowing the drifter to visit different depths in the water column.
The 2009 drifter is presently in the final stages of prototyping before mass production begins this winter. Check out the photos and videos below for more information.
The 2008 drifter maintained the two-hull design but expanded the machined aluminum flanges and bulkheads to allow a differential drive propeller system. The vertical cylinder profile, which is important for accurately capturing the velocity of the water, makes the vehicle dynamics challenging. Our lab experiments showed that control of the device with the two propellers was indeed feasible.
The aluminum sealing system was changed from a face-and-plate system to a cylindrical seal. This allowed the propeller shaft bearings to be integrated into the machined aluminum parts, and promised to be a more robust sealing system.
2007 Model 2
Our first step toward an actuated drifter was the development of a prototype based on the 2007 passive drifter. A single rotating motor pod was added to the bottom hull. With an electronic compass and external power, the device was a proof of concept of drifter mobility; it also allowed us to further develop our fiberglass manufacturing techniques. Ultimately, we chose not to continue with the single pod design.
The drifter project began in 2007. The two-hull design had a "wet" hull on the bottom for water-facing sensors, and a "dry" hull above for electronics. The waterproof sealing flanges and bulkhead were machined aluminum, and the rest of the hull was a combination of cast fiberglass, fiberglass pipe, and vacuum formed polycarbonate. The main bulkhead contained two modular sensor mounts to allow mounting a variety of sensors.