Radio Control Systems

By Paul Williams.
Article posted 1st March 2008.

Problems with radio control systems seem to plague FE boaters. This is not surprising, given the harsh environment these delicate electronic components have to tolerate. High humidity, high temperatures, motor noise and vibration combine to make life difficult for receivers and servos.

Blaming the environment, however, cannot mask the fact that many FE boaters do themselves no favours when fitting out their radio system. Some of the cardinal sins I've seen committed include cutting the original aerial wire. Do not do this. The aerial is meant to be a fixed unbroken length. Altering the tuned length and introducing connectors immediately compromises the receiver's ability to pick up a clean signal. Run the aerial wire vertically up and out of the boat through a length of thin plastic tube.

Cheaper radios often have very long aerial wires. Don't be tempted to coil up the excess length of aerial inside the boat. Run the whole length up and out, securing the aerial end to the base of the aerial tube. When the boat is running, the slipstream will pull the aerial into an open loop.

Racing boats really only need two channels: on and off, and left and right. They usually don't require huge range like a model aircraft. The best advice regarding radio systems is to buy the very best you can afford. If it's a choice between spending out on a better, more reliable radio or a more powerful motor, consider this: the more powerful motor will smash your boat into a wall or other object harder when the radio fails! Avoid really cheap radio sets. They don't have the range or signal processing/interference rejection of more expensive sets and are a false economy. It's quite easy to spend many hundreds of pounds on a high speed model. Do you really want to risk that kind of investment by skimping on a decent radio set?

A cheap radio may work faultlessly when testing on your own, but in a race may glitch like crazy in the company of another 7 or so radios. Smacking into another competitor's boat because your radio can't cope will earn you no friends and will probably get you disqualified.

40Mhz or 2.4GHz?

There are two frequency bands available to surface models in the UK: 40 MHz FM and 2.4GHz. 40MHz is the "traditional" frequency band and has been in use for many years. 40MHz sets run on a single pre-determined channel or frequency, set by either changing the crystals in the receiver and transmitter, or by dialling in the required channel on a synthesised set. 2.4GHz sets constantly hop around the frequency band and can detect and automatically avoid clashing with other 2.4GHz sets in range. There's a lot more to 2.4GHz than this and Google is a good place to start if you want to know more. For simplicity's sake, all we need to know about 2.4GHz is that you don't need to worry about frequency control anymore and that the aerials are conveniently very short and thus easier to install and less likely to be damaged.

Unfortunately, I'm now very hesitant to recommend 2.4GHz for fast electrics. My own experience of 2.4GHz was not a happy one, and after a near disaster the one and only time I tried it in a race (total loss of control and a failure of the radio to fail-safe) I sold my 2.4GHz Futaba 3GR set on ebay and went back to 40MHz. That said, there are many FE racers who are very happy with 2.4GHz.

In my opinion the jury is still out on whether 2.4GHz really works reliably enough for powerboats, given that powerboats tend to throw huge amounts of water into the air from propellers, turn fins and rudders, and the one thing a very high frequency signal has trouble punching through is a dense, attenuative medium like water.

At this point, some of you are wondering "What about 27MHz?". Well, what about 27MHz? Ok, it's legal to run FE boats on this part of the spectrum, but is it a wise thing to do? No. Absolutely 100% NO. 27MHz is now so prone to interference, I cannot advise strongly enough that FE boaters avoid this type of radio. Stick with 40MHz FM or 2.4GHz and leave 27MHz to the scale boaters and yachts.

Delicate electronics and water don't mix. It's inevitable that you'll get some water into your boat at some point. Assume the RX will get wet and act accordingly. Carefully remove the RX board from its case and apply multiple coats of PCB laquer or a conformal coating so that the RX will continue to function even when fully submerged.

Servos are another item that FE boaters tend to skimp on. Standard servos often struggle to cope with the rudder forces experienced in today's high speed models. A cheap servo will often have a fair amount of slack and may not centre itself in the same position every time. This means the boat can never be driven "hands off" along the straights, and the constant steering input prevents the boat achieving its top speed.

High quality, digital, metal geared, ball-raced servos are a must for a high performance boat. Losing control of a valuable, high-performance model powerboat is not only going to be expensive and painful to watch. Imagine how much energy a 2kg hydroplane travelling at 50mph possesses - more than enough to seriously injure or kill. No, the radio control set is a safety critical system and the one area of the boat where you really must not economise.

Good quality servos are a waste of money if you don't mount them correctly in the boat. Servo tape is not good enough. A servo needs to be bolted to a rigid wood, metal or carbon fibre mounting, and you need to use good quality components in the linkage. Balljoints or metal clevis clips on each end of a metal pushrod will ensure that the precision of the servo is transmitted to the rudder. Worn rudder bearings that allow the rudder to flop around reduce steering response and can allow the rudder to "flutter" at high speed, transmitting a damaging vibration back into the servo. Any amount of play in the rudder or linkage needs to be addressed.

Hitec HS5245 metal geared, ball-raced digital servo fitted with anodised aluminium output arm, secured in a wooden mount made from oak strip and 0.6mm ply.

The rudder on this tunnel hull is connected to the servo with a linkage made from 3mm diameter carbon rod. The ball-joint ends are glued to the carbon rod with Loctite 603.

The strut and rudder brackets are braced with a length of 8mm diameter carbon tube. I made the rudder arm from a piece of 3/8" diameter aluminium bar and a length of 1/8" stainless rod.

The majority of problems that people have with their radio control systems might seem a mystery to them. However, there's no real mystery to it at all: cheap, low-grade components combined with poor installation and non-existent maintenance = trouble. Buy good quality, branded gear from the likes of Futaba, JR or Hitec, install it properly and look after it and you really shouldn't have problems. If it gets wet, remove it from the boat, dismantle the case and allow it to dry thoroughly.

A quick look around eBay rapidly yields thousands of r/c items for sale, many at stunningly low prices, prices that are literally too good to be true. Seriously, do you really think it's a good idea to trust safety and a large investment in time and money to unbranded components that have cost almost literally peanuts? Some of these incredibly cheap Chinese servos have a lifespan measured in minutes. If they cause the destruction of a model that's taken you weeks to build and cost £400+, where's the saving? That's right: in bits at the bottom of a lake. Yes, most branded r/c kit nowadays is made in China. However, Futaba, JR and Hitec all have hard won reputations at stake and they ensure some minimum levels of quality control are adhered to. Plus, they offer a warranty, something that might, strangely enough, be missing from stuff bought on eBay from halfway around the world.

© Copyright Paul Williams and www.fastelectrics.net, 2010.

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Last modified: 08th July 2010 @ 09:06