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RADIOS - Check with the local fleet about open frequencies before
purchasing, and be sure you are getting a radio with a surface frequency,
usually 75 MHz, or 27 MHz. You don't want to interfere with an airplane
operating in the area. Most radio transmitter/receiver sets come with one or more servos,
one of which can be used as the steering servo. In some cases, however, it may
be advisable to obtain a faster and smoother operating servo, probably not
included in the basic sets. There are two types of radios: Standard radio, transmitter and servo sets, low cost and no frills.
You will notice that the lowest price radios are AM, and as you move up you get into FM. There is a good explanation about the differences between these two methods of transmission on the KBits site, but usually FM has less chance of interference. (KBits is in England, so they use 40 MHz instead of 75 MHz.) Computer radio, transmitter and servo sets (boat can be adjusted from transmitter), more costly and may contain extra features which you may or may not be able to use. This style of radio can often be fitted with HAM frequencies for fewer duplications. Many computer radios have the ability to use an adjustable exponential curve for the steering stick, so as you are making small adjustments to your course, it helps to keep you from over steering.
SERVOS - What do you need? The airplane guru where I got my JR radio says the following in his catalog:
This looks like it leads you to a fast, double ball bearing, coreless, zero deadband servo with “enough” torque. From a JR chart I have examined, the servo cost is about $75. You will find helpful charts on the AMYA site at these links: I was initially advised to purchasing a digital servo, so I ended up trading the four servos that came with my radio for one 8231 Ultra-Precision Digital Servo by JR. So, the Duck’s servo has the following characteristics; from the manufacturers data sheet:
The specifications seem to match
the serious questions, except I do not really know if the 88 oz./in. of torque
is enough or too much. However, I have never felt that the boat was going anywhere except
where it was pointed by me. I have not been out in #3 weather, but if your rig
is right and trimmed properly, the torque required should not go up
substantially. JR has some new, lightweight digital servos, and I may try the DS368 which costs about $70, and has 53 oz./in. of torque, a speed of .21 sec, and weighs only .80 oz., a savings of nearly an ounce, and 30 bucks. For some additional thoughts
about the steering systems in your boat, take a look at an English web site by
Ken Binks at KBits. He specializes
in Futaba servos and has quite a rundown on several. As you look at his site, to
convert the torque rating from kg./cm. to oz./in. multiply by 13.9. You will see
that his safe, middle of the road servo seems to also be in the $72 to $86
range, with torques of 69 to 100 oz./in. An interesting point is that the
Futaba Attack 2 radio, a very economical radio, comes with model 3003 servos,
which costs $7 and have a torque of 42 oz./in. Ken’s ultimate is a digital,
coreless servo, Futaba model 9450, with a torque of 111 oz./in. and a cost of
$127. BATTERIES - Most everyone runs on a 5 pack of AA rechargeable batteries in the boat and of course you want as much electricity as you can store. We have bought packs made up for us at Batteries Plus, a retailer of batteries who will make it up to your specifications. They do not have the batteries with the highest milliamp ratings but they are close, at this time they are supplying 1600 mAh AA cells. We have been using Nickel Metal Hydride (NiMH) because they do not have a memory like Ni-Cad batteries. You can usually find some sort of battery store in town if Batteries Plus doesn’t exist where you are. A web site with some good information about the state of the art in batteries is Small Power. You will find that you can get 1600 NiMH mAh AA cells from them also. Another good site is Thomas Distributing, and they have quite a selection of AA NiMH batteries At about $3.70 per battery, you are looking at about $48 for a really good set of 13 batteries, now you need some way to charge them. CHARGERS -Many of the radios above the very basic level come with batteries and chargers. Some of the sites you have been directed to also stock several kinds of chargers. Ask around at the pond about the latest in chargers. I am still using the one supplied with my radio and a modification of an inexpensive Radio Shack unit. I have had a simple charger recommended, it is a Hobbico
and several types
can be ordered from Tower
Hobbies Chargers in the $20 to $60 range. The unit will have to have adapters added to fit your battery
packs, and the premade units are about $9 each. |
Where
to now?
The perfect launch!
01/09/2006 |
