RC systems for boats
- how your rc boat is controlled
It's important to understand how your rc boat system works, in order for you to get the most out of it.
Entry level rc boats are almost always 2 channel, which means that you have control over 2 functions; either engine and rudder if the boat is powered by a motor, or rudder and sail movement if the boat is a sailboat with no motor (some sailboats do have small electric motors, which would be a 3rd channel).
On bigger, particularly scale, rc boats there may be more channels; for example the boat may be a model fire-fighting boat with working water cannon, or extra rc functions might include working navigation lights, lifeboat davits, fog horn etc.
RC systems for boats, as well as for cars and aircraft, are mostly proportional. In other words, if you move the throttle stick of the transmitter only a small amount, then the engine will only increase slightly; move it all the way and the engine will open right up. And the same with the steering, if you just move the tx stick or wheel slightly then the model will only turn slightly.
So with a proportional rc system, whatever input you make at the transmitter is directly represented in the model. Basically, having a fully proportional rc set means that you always have complete and precise control of your boat.
Transmitter (abbreviated to 'Tx')
The transmitter is the main body of the rc system, the part that you hold and use to control your boat.
Transmitters for boats can either be the pistol grip style or the traditional 2-stick type. Generally speaking, an rc boat with either an electric or nitro motor will be controlled with the pistol grip type tx, whereas a sailboat will be controlled with a stick tx.
These two very different styles of transmitter are shown below:
A pistol grip tx can be held in 2 ways, depending on whether you're right or left handed. Use your index finger on the trigger, and your index finger and thumb of the other hand to turn the wheel. You may find that you're more comfortable with it one way than the other, regardless of whether you're right or left handed. It's really just a case of 'suck it and see'!
Above, 2 ways to hold a pistol grip style rc transmitter
When using any radio control transmitter for an rc model, it's very important to always have the transmitter antenna fully extended. If it's not, then the range of the radio system is drastically reduced and you'll very quickly lose control of your boat.
Receiver (abbreviated to 'Rx')
In the same way as a traditional radio or television receives a signal from its broadcasting station, an rc receiver receives the signal that is emitted by the tx when any input is made by you.
The receiver is located inside the boat and is directly connected to the servos by small leads. A thin gauge wire antenna runs from inside the rx to outside of the model. This antenna should never be cut or looped up to reduce its length; in doing so, its ability to receive the signal from the transmitter is drastically reduced, and this almost always has disastrous consequences by way of your boat going out of radio range too early.
The radio signals, once received by the rx, are spontaneously passed through to the servos which then move in direct response to the signals. This whole process of the signals passing from tx to rx, then on to the servos, is called modulation and can be digital (more common) or analogue (not so common nowadays).
Servos
A servo consists of a plastic outer casing, inside which is a small but powerful electric motor connected to either plastic or metal gears. These gears are connected to the servo horn, or arm, located on the top (exterior) of the servo body. This horn is the 'hand' of the servo and links directly to the controllable features of the boat ie the motor throttle and rudder.
One separate servo is needed for each channel, and connects to the motor or rudder by servo rods, fine gauge wire or plastic lengths with plastic or metal cleats at each end.
When a signal from the tx is received by the rx, it travels through to the servo. The circuitry inside the servo tells the motor how much to move and in which direction. This movement of the servo motor rotates the gears, and hence the servo horn and rod. This final movement of the rod controls that particular operation of the boat, whether it's opening or closing the throttle or turning the rudder.
Another kind of servo used in rc sailboats is called a winch servo, shown below in comparison to a standard servo:
Winch servos have a pulley wheel in place of the horn, and they are hooked up to the boat's rigging. Operating the servo winds in or winds out the fine cord that connects the winch servo to the sails.
Winch servo motors have to be more powerful because of the weight of wind in the sail, they need a lot of torque to operate effectively.
RC Crystals
Crystals determine which frequency channel the rc set will operate on. For rc boats, a set number of channels have been designated within the 75MHz and 27MHz frequency bands. Both of these frequency bands also cover rc cars and trucks, and rc surface vehicles in general (see all the rc boat frequencies).
Both the transmitter and the receiver need their own crystal to operate correctly, and they must match frequency exactly. The specific frequency of the crystals determines your channel number or color.
Although you can't change the main frequency band of your rc set (ie from 75MHz to 27MHz), you can change the channel number or color within that band, simply by putting in a different set of crystals. In fact, it's always a good idea to carry at least one spare set of crystals with you, so that you can change channel at anytime if other boaters are occupying your usual channel. When buying extra crystals, try and choose a range of widely spread channel numbers.
Batteries
The most common battery cell size for rc boat systems is the AA 'torchlight' size. It's normal for the transmitter to take 6 or 8 cells, and the receiver 4. However, many modern RTR electric boats don't require separate receiver batteries but instead take the rx and servo power from the motor battery pack.
RC systems don't consume batteries too quickly, but obviously with very regular use you do need to be aware of the power level of the batteries. A full day's boating is usually enough to drain the overall battery level to a critical one. Low battery levels - even if just one cell is flat - can, and will, result in your boat going out of radio range sooner than expected, with the consequent loss of control.
It's a very good idea to buy rechargeable batteries if you can. Nickel Cadmium (NiCD, or 'nicads') and Nickel Metal Hydride (NiMH) cells are commonly used in rc boat systems. NiMH cells have greater capacity and performance than NiCD, and are now the preferred choice. NiCDs are becoming outdated, although still in use at the moment.
Rechargeable batteries are pricier to buy than 'dry' (non-rechargeable) ones, but they soon pay for themselves. Typical NiCD or NiMH batteries last for around 1000 charges, so that's a lot of rc boating!
Always be very aware of the battery level in your rc system. Radio control transmitter battery meters, where used, are quite accurate so you should be able to tell the state of the batteries from that. If in doubt, charge or replace!
If your transmitter doesn't have a meter, it would be well worth investing in a small handheld electrical voltmeter to check your battery levels. If the battery level is low, then your boat will go out of range quickly and you'll lose complete control.
Spread Spectrum RC boat systems
All the information above relates to the standard 75 or 27MHz rc boat systems, but many modern systems now make use of the new 2.4GHz 'spread spectrum' radio technology. The fundamentals are the same, but there's a big difference in how the transmitter and receiver communicate with each other.
Essentially, when you turn on the tx and rx they scan the designated rc 2.4GHz frequency channels until a free one is found, then they lock or 'bind' together on this channel. A second channel is also locked on to, so if the first one fails for any reason then there is a back-up channel that the system can still operate on. Once bound, the channels become secure and impermeable to any interference.
Spread Spectrum radio sets are becoming more and more common, rapidly replacing 75MHz sets. The instant response and secure channel bond between tx and rx ensure worry-free control of your model, with exact and precise control provided through digital servos.
See a choice of rc boat systems here, including 2.4GHz sets.
Related pages
RC boat frequencies - designated channels for rc surface vehicles.
RC gear for aircraft - an overview of rc systems for planes.
