The decision was made to build a human-powered jellyfish. Now how do we do it? While continuing to update my jellyfish files and working on a schedule I’ve started to write up a set of design parameters for the sub. Although I’m sure that there are any number of ways to accomplish the same or better end results most of my design decisions are based on available funds and the extreme limitations of my home shop.
1. Race Category: The sub will be entered into the one-person non-propeller category. This is being done to keep the size, complexity of the pedal drive mechanism and costs low. It also allows us to transport the sub in a van instead of a trailer or larger truck.
2. Size: Approximately 8-10 feet long with an 8-10 foot diameter bell. The bell will be able to be pulled down to 4 feet in diameter for transport and launching. I’ve got a 7-1/2 foot ceiling in my garage. This will proove interesting.
3. Layout: The operator will be in a prone position in a cylindrical hull in the center of the bell. A plastic hemisphere at the end of the hull will allow excellent visibility not only for the operator but also for the support and safety divers. Entry and exit of the operator will be through this hemisphere. This will eliminate the need to go into the bell to access the sub.
4. Pedal Mechanism: We will use a conventional bicycle type pedal drive. This will give the most flexibility for varying the gear ratio to the final drive, it’s very simple and reliable and pretty efficient. The main concern is that if we use pedal clips on the pedals it may be difficult to provide access to the pedals for the support diver if they have to extract the operator, toe clips may be better.
5. Bell Operating Mechanism: The pedals will operate a scotch yoke mechanism which in turn will make the bell open and close. At least it sounds simple.
6. Bell Construction: Ideally I would like to use a cast silicone bell with internal ribs. This would give the appearance of a jellyfish, would stretch and shrink during the open and close motion and would allow the simulated bioluminescence to show through. Aside from the cost of the silicone, making a suitable mold and having enough horsepower to stretch it open, how hard can this be?
7. Steering and Depth Control: To be finalized. Some of the ideas are a rudder and stern planes ( easiest, but neither of which a jellyfish has), articulate the hull to bend and use that for directional control, having the bell articulated so that it would be pointed in the direction we want to go or my favorite, inertial directional control with no external control surfaces.
8. Ballast: The sub will initially be ballasted to a neutrally buoyant condition. On board ballast tanks will allow for fine tuning.
9. Trim: Trim tank bow and stern with a reversible water pump to move water between the tanks.
10. Safety Features: Per ISR sub guidelines
11. Speed: Right now we are just looking a making it down the course before the operator runs through his tank of air. The fun will be in making the propulsion system work. Next race we’ll go for speed.
12. Cost: Under $5,000
Next entry should have some sketches.