RC Submarine Electronic Modules Explained
I've said it before and I'll keep saying it... RC subs are hard.
One aspect that can be daunting is the myriad of various electronic devices that aid a submarine in safe, efficient and fun operation. There are a number of manufacturers out there that offer these devices, and while some go about the task differently, the task that they're accomplishing is basically the same.
I represent the superb line of electronics designed and produced by Kevin McLeod out of Canada, though I also offer products from MTroniks and some other manufacturers who offer products that Kevin does not currently supply.
Let's take a quick look at the various devices and what they do for your boat:
Electronic Speed Controllers (ESC)
ESC's are needed in order to translate inputs from your transmitter into a proportional voltage output for your main drive motors. The further you push your stick, the more voltage is applied to your motors, hence faster RPM's and a faster boat. Most ESC's available for subs will have full reversing, so you have proportional control forward and in reverse. Most modern ESC's also have built-in BEC's (described below).
Battery Eliminator/Voltage Regulator (BEC):
BEC's take the input voltage from your main drive batteries (normally between 7V and 14V) and cut it back to a lower voltage that servos and other RC gear can accept (around 5V to 6V). BEC's will be rated for a certain ampere output load, so be sure that whatever you're plugging in does not exceed that rating. Servos are quite efficient, but some peripheral electronics can suck a lot of amps.
Automatic Pitch Controller
APC's are designed to help stop the embarrassing (and potentially fatal to a sub) porpoising effect that happens when a sub operator attempts to maintain an even keel while under operation. What happens in most cases is that the sub begins to dive, the operator over-corrects, the sub rises, the operator over-corrects, and you end up with your boat alternating between surfacing and diving, looking like a dolphin trying to breach the surface. The APC uses an internal sensor to detect when the boat is pitched forward or back, and sends corrections via the dive plane servos. The sensors are very precise and fast, and can keep a boat at a perfectly level operation without the operator needing to provide any inputs whatsoever. At any time, however, the operator can override the APC to command a dive or surface. APC's are typically installed between the receiver and the rear dive plane servo. They can also operate autonomously, without the need for a channel, provided they are given 5V power.
This functionality is often found built in to other devices, but there are standalone failsafes that can be installed in any circuit. The idea is that the unit watches the input commands coming from the transmitter. If and when the commands disappear or are scrambled, the unit sends a pre-defined command to the boat, typically to the ballast system to command a blow and surface the boat. The most common reason for loss of signal is diving too deep in the water.
There are a few different variations of this functionality. My BLM module, for example, monitors the voltage of your Lithium Polymer batteries and also integrates a ballast failsafe in case of loss of signal or low voltage. Alternatively, and for those with a bigger boat, there are units such as the Watt's Up display that gives visual readouts of battery voltage, current draw and a number of other insightful data points. Regardless of the specific features, these units generally offer information on the status of your batteries and when it is time to bring the boat in for a recharge.
Mechanical on/off switches are fine, but they require a physical hole to be cut into your watertight compartment, which is a potential ingress point for water. Remote switches offer increased convenience and fewer ports in your compartment. Most remote switches are of the magnetic variety where you simply swipe a magnet over a specific area of your cylinder or hull to turn the model on and off. I also offer RF (radio frequency) switches that allow you to turn your boat on/off from a distance of several meters, just like unlocking the doors on your car with a key fob.
Some boats utilize an "X" configuration for the rear control surfaces rather than the standard cruciform setup. This offers increased maneuverability as you have all four control surfaces moving at the same time to control both pitch and yaw. In order to accomplish this, however, you need to mix signals from the horizontal and vertical servos. These electronic units do just that. You simply plug in your rudder and dive plane servos into the unit and it automatically mixes the outputs depending on what you're trying to accomplish.
These units utilize a small port in the watertight compartment to allow ambient water pressure to act against a pressure sensor on the unit in order to offer relative depth information. Engel has been including these with their ballast systems for a long time, and they allow static hovering of a boat when tied through their ballast control systems to a pair of piston tanks. Another variation that I offer is typically installed between the receiver and front dive plane servos. During operation, the unit remembers the depth of the boat when you last provided input to the front planes. It then keeps the boat at that depth using the bow planes until the depth is overridden by the operator.
These units provide more scale-like speeds from a servo. Typically, when a servo is actuated via a two-way switch on the transmitter, for example, it quickly cycles from one limit to the next in the space of less than a second. The GoSlow allows the same travel, but slows the operation down by a user-selectable rate. This is perfect for more scale-like speeds for torpedo tube doors, bow retracts, periscopes, etc.
Bow Plane Interlock
A handy unit to ensure that you don't damage your bow plane linkages on retractable bow planes. This unit locks out the bow plane servo unless the bow planes are fully extended.
Pump Controllers / Electronic Switches
These electronics are typically used to allow the control of a ballast pump. The units that Kevin manufactures will activate the air pump when the transmitter stick is pushed in one direction, and will actuate an electronic valve when pushed in the opposite. This is perfect for both SAS and RCABS ballast systems. At their heart, electronic switches are simply a set of electronic relays that allow power through depending on the position of the control stick.
I'm sure that I've forgotten some other electronics, but these are the main ones that you'll see installed in a sub. Not all are required, or even applicable to most boats, but each serve a purpose, be it for safe operation, ease of use, or just plain old cool features.