Ballast Systems

Overview

There are many ways to control the depth of a submersible, ranging from thrusters to weights, bladders to ballast. This page serves as a research hub for compiling descriptions of these methods. Some of these methods have been built by the Robolab, and have documentation links following their descriptions. All methods have cited courses links.

Methods

1. Recirculating Air Ballast System (RCABS): This method uses a pump to inflate a bladder using air from within the main pressure vessel. This increases the subs buoyancy, causing it to rise. When the sub is to dive, the valve is opened and the vaccuum in the pressure vessel draws air out, making the sub sink. It is worth noting that the default state of this sub is heavier than water, and hence needs a separate failsafe system. (reference) (documentation)
2. Reverse-RCABS (RCABS-R): Popular in the model submarine community, this method is similar to RCABS (described in #1), but instead of drawing air from the pressure vessel, the air is drawn from a compressed canister. This new design means that the default state is air filling the bladder, hence allowing the sub to float. (reference)
3. Gas Ballast System: This method uses a water-filled ballast tank to add weight, allowing the sub to sink. To remove the water, this system uses a canister of low pressure gas, released using a servo to purge the ballast tank of water and allow the sub to rise. Because of the gas canister, this system has limited uses before the gas runs out, and thus must be monitored. The water comes in through holes in the bottom of the sub when gas is released through a vent out the top, and when the vent is closed and gas is released, the water is pushed back out the holes in the bottom. (reference)
4. Piston Tank Ballast System: This method promises to be the most electronically challenging, but offer the most control over the vehicle. The system uses a piston powered by a motor to pull water in or push water out. The ballast tank size is dictated by the size and length of the piston. Partial retraction of the piston can allow the sub to hold depth fairly accurately. It is a hard system to build. (reference)
5. Low Pressure Pump Ballast System: This system involves a ballast tank and a vent similar to the Gas Ballast System (described in #3). However, instead of storing gas onboard, the submarine has to surface to empty the tank, drawing air from the outside to push the water out of the tank. This requires the sub to be constantly positively buoyant, which means that the ballast tank merely reduces the sub's buoyancy enough to allow it to dynamically dive underwater. This is a safe system because it is always able to float to the surface, but cannot hold a position in the water column due to the dynamic diving. (reference) (documentation)
6. High Pressure Pump Ballast System: This system is similar to the Low Pressure Pump Ballast System (described in #5), but instead of letting the air vent and having to surface to regain it, this system pumps in water and compresses the air inside. This allows the submersible to change its buoyancy without having to surface, and also allows it to be negatively buoyant without problems. It is worth noting that a high-pressure pump is necessary for this system. (reference)