| |
|
|
R/C Submarine Basics
Diving Systems: "Static vs. Dynamic"
A Static Diving System is one where an object submerges (dives) by changing it's overall weight. This typically occurs through the use of an onboard ballest system and can occur when the object is stationary. In contrast, a Dynamic Diving System, is one where dynamic forces are needed to overcome the objects buoyancy. These forces are generally in the form of a sufficient forward speed in combination with a set of hydroplanes (forward or aft), which will then "push" the object under the water. As long as these forces are present, the object will stay submerged.
Ballest Systems: "Electric, Pump, Gas. . ."
See our sample SubCommittee Report articles about this and other topics directly from the SubCommittee Report.
Various Internal Electronic Systems
See our sample SubCommittee Report articles about this and other topics directly from the SubCommittee Report.
How many Channels will I need?
With a dynamic diving submarine, 3 channels (throttle, diving planes, rudder) is the minimum. Add another channel if you want active ballest control. Then add another for torpedoes, or periscopes, another for side thrusters or other bells and whistles...
How far will my signal transmit under the water?
This will vary on the amount of dissolved materials/metals in the water. The deeper you go the more scattering of the signal. The Cleaner the water.... usually the better the Reception and the lessening to the Attenuation of the Broacast signal.
Overall, a depth of 5-10 feet fairly common.
Types of water in order of Best Reception/Transmission of Broadcast Signal:
Deionized Water
Tap Water
Chlorinated Pool Water
Fresh Water
Brackesh (Most Still Pond Water)
River Water
Ocean Water
How to determine antenna length and general radio signal information
Submitted by Warren Wilson
Antenna Length
One formula has a constant of 234 divided by the frequency in Megahertz, answer is in feet. Another variation is 300 divided by the frequency in Megahertz, divide by 4, reduce the length by approximately 5 percent, answer is in meters. In each case the answer is for a quarter wave antenna. A meter is 39.37 inches.
For example 75.700 MHz is mid-point of the frequencies for surface use in the Americas. The first formula results in an answer of 3.09 feet, or 37 inches. The second formula yields the same with differences insignificant.
A question often asked is how far will a radio control a model craft. An answer is very difficult to determine as many factors influence the range that control may be maintained. Some of the major factors are; antenna placement in the model craft; electrical noise in the model; frequency of the transmitter and receiver, strength of the transmitter and its antenna; others operating on adjacent channels.
Generally for model submarines there are few options for the placement of an antenna. Most commonly the antenna is laid horizontally lengthwise in the boat. It is very important is to keep the antenna wire away from any motor, it’s power leads and controller, while avoiding metal objects. If an antenna needs to double back, make the loop as large as possible. For small boats it may be necessary to coil the antenna wire. In that case the loops should be large with open spacing. Tight coils should be avoided and if necessary they should be at the far end of the antenna wire.
At extended range its best with an antenna horizontal in a boat to hold the transmitter antenna horizontal roughly parallel to the boat antenna.
Frequency of Radios
Frequencies employed in the Americas will carry over water a bit further but penetrate to a lesser depth. European frequencies are likely to have slightly less range and will penetrate the water a bit deeper. Most radios used in model boating are adapted from those for aircraft where operating range is important and sufficient power is available. Commonly model boating is conducted with the boat close to shore or the driver, consequently it’s unusual to be limited in range because of transmitter power.
Electrical Noise
This frequently is the major factor determining operating range. In the majority of cases it's also the most difficult problem to solve. One boat may be built without any regard for noise reduction and work well while another be built with attention given to electrical details and be frustratingly plagued with problems. Electrical noise can never be eliminated, only reduced in intensity to where everything works acceptably.
Common Point
This will vary in each boat, and many successful boats will not have one distinct or defined common reference point. However, good engineering practice highly recommends, actually requires, that there be one common point for all negative wires of loads to be attached to. The negative battery terminal connects to this point. It must be emphasized that each device, especially motors/controllers which have a large amount of current flow has it’s own individual negative wire routed to the common point. Don’t string or connect wires, from devices, which have current flow, together one after another ending up at the common point. Yes, it may seem wrong to have a number of wires from the same general place going to the common point, however, it’s best. The location of the common point should be somewhat central but it should be close to the loads with the highest power loads and the negative terminal of the battery. The larger the boat, with consequently higher power drains, the more important it is to have a common junction point for all negative leads. This is known as preventing ground loops.
Noise Suppression
Perhaps the most important thing is to have capacitors installed on motors to suppress brush noise. Three capacitors are needed on each motor. One across the brushes or motor leads, if the motor has a metal case then a capacitor from each lead to the case. Capacitors should be connected as close to the motor as possible with short leads. Generally soldering is necessary. A wire should be run from the motor case to the common point, usually the negative battery terminal. Two motors can be connected to one shield or drain wire. Nothing else should be connected to this wire. The value of the capacitor isn’t critical. Suggested values are 1000 pF, 0.001 microFarad, or 1 nanoFarad, voltage rating should be 50 volts or higher. If in the rare case that one motor lead is connected to the case, do not install the shield or drain wire.
In some cases of severe motor noise a toroid core on the power leads may be needed. Four or more turns should be wound on the core. Both motor leads are to be threaded through together in the same direction. Cores found around computer power leads will work well. The core should be as close to the motor as possible after the capacitors.
Servos are suppressed at the factory and should not need changing. Sometimes when servos are next to each other cross coupling can cause problems. Placing a piece of shielding metal between them or increasing the space between them will correct the problem. A wire from the shield to the common point is necessary.
Stuffing tubes for propeller shafts should have a shield or drain wire connected to the common point. Boats with multiple tubes may have them connected together and then routed to the common point. In rare cases it may be necessary to have a brush on the propeller shaft.
All wires, especially power wires running any appreciable length should be twisted together.
All large metal objects should be connected to the common point. It is acceptable to connect them together one after another as long as there isn’t any current flow present.
The best way to eliminate electrical noise to plan prevention in at the beginning when building the boat. Noise reduction after the fact becomes experimentation for solutions. Sometimes as a trouble shooting aid a small battery powered AM radio can be used. Tune the radio to the low end of the dial to a spot free of a radio station and turn the volume up high. While operating different portions of the boat listen for the crackle of static which changes as you operate different portions the boat.
|
|
|
