What's the Frequency, Kenneth?

about the mission

R/C submarines utilize three essential electronic components to affect control: a radio transmitter, a receiver and servos. These basic components are the same ones that have been used for years to control R/C airplanes, cars and boats.

Radio transmitters contain control sticks and switches which the operator manipulates to send commands to the model. The transmitter multiplexes all the commands into a single pulse-position modulation radio signal. In most cases, the number of control interfaces on the model dictates the number of channels the radio must provide. Dynamic diving submarines normally require three channels: throttle, rudder and stern planes. Static diving submarines require a minimum of four channels: throttle, rudder, stern planes and ballast system.

The receiver is mounted in the model and receives the radio signal through an antenna. It demodulates and demultiplexes the signal and translates it to the pulse-width modulation used by standard R/C servos or electronic speed controls (ESC).

Hard connected to the receiver, servos contain a small motor in a case that drives a control horn mounted on the top of the case. The control horn moves in response to the receiver command. The motion is transferred by a hard linkage to the control surface.

R/C Hobby Development

The first instance of an underwater craft being controlled by radio occurred in 1909. The French inventor Gustav Gabet unveiled a radio controlled torpedo designed for military use. It wasn’t until the 1950’s that R/C systems began to be commercially available to modelers.

In both tube and early transistor sets, a model's control surfaces were usually operated by an electromagnetic escapement controlling the stored energy in a rubber-band loop. Control consisted of simple on/off commands.

Crystal-controlled superheterodyne receivers increased capability at a lower cost. As the electronics revolution grew, proportionally coded signal streams were used to control R/C servos. This technology opened the door for the growth experienced by the R/C model submarine hobby in the 1980’s and 90’s.

The 21st century has seen a shift by manufacturers to 2.4GHz transmissions which have begun to dominate control of model vehicles and aircraft. Unfortunately, this frequency range will not penetrate water and is unsuitable for submarine use. Pulse-code modulation (PCM) features provide a computerized digital bit-stream signal to the receiving device, instead of analog-type pulse modulation.

Radio Frequencies

Today’s hobby grade R/C systems have modular designs making it possible to move R/C equipment from a car, boat, or airplane and use them in a submarine. However, moving the receiver between aircraft and surface vehicles is illegal in most countries.

Radio frequency laws allocate separate bands for air and surface models. This prevents interference between model aircraft and surface vehicle transmitters and enhances safety. For example, in the United States, model submarines fall into the Surface Use Only (75 MHz) category along with cars, boats and other non-flying models. The F.C.C. restricts use to a radio tuned to 75MHz on Channels 61-90. Utilizing radios tuned to frequencies reserved for other types of models is illegal. Please check the regulations in your country to ensure that you are using the correct frequency band (Canada is 75 MHz; UK, Germany and most of Europe is 40 MHz).

The specific channel is usually determined by the crystal inserted into the receiver and the transmitter. The channel can be changed by simply changing the pair of crystals for a set tuned to a different channel. Some radios and receivers are capable of synthesizing different channels within their assigned band, thus allowing a channel switch without requiring a change in crystal.

Modern computer radios allow functions to be adjusted over several parameters for ease in setup and adjustment of the model. Many of these transmitters are capable of mixing several functions at once, which is required for some models. Settings for multiple models can be stored in memory for reuse.

Radio Reception

A key issue in radio performance for model submarines is frequency attenuation. Frequency attenuation is the tendency of particulate matter in the water to interfere with radio signal transmission. The higher the solids content in the water the model is operating in, the poorer the signal reception will be by the receiver in the model. Clean, fresh water is the optimal environment for maximizing reception. Though optically clear, signal reception tends to degrade in heavily chlorinated swimming pools. Range is further lost in brackish fresh water. Saltwater will not permit submerged reception; an antenna must be above the surface to ensure uninterrupted control of the model.

Placement of the receiver antenna can also affect signal reception range. To maximize reception, the antenna should be looped within the hull of a model. In wet hull boats a brass or stainless steel stud is threaded through a bulkhead and the antenna is cut at the break. The receiver end is fastened to the dry side of the bulkhead stud. The rest of the antenna is fastened to the wet side of the bulkhead and looped in the hull.

When the receiver antenna is placed in the wet area, it is vital that the antenna be insulated from the water, both at the connection point at the bulklhead and at the very end of the antenna itself. To not do so will cause the antenna to become grounded, which will effectively prevent signal reception from the transmitter. Care should also be taken not to change the overall length of stock receiver antennas as they are tuned for maximum efficiency at the factory.

Stock receiver antennas can be looped around a piece of wood or plastic and stowed in the WTC to save space. Care must be taken to ensure the antenna loops do not touch themselves. This configuration tends to reduce reception range. However, it is usually more than sufficient for running a model in swimming pools or other small bodies of water.

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Bubblehead Vocab

learn the R/C sub lingo

  • Radio Transmitter
  • Receiver
  • Servo
  • Frequency Attenuation
  • Antenna

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Best Practice

  • When powering up the radio system in a model, always turn on the transmitter first before turning on the receiver. During shut down, always turn off the receiver first, then the transmitter.