pirespreto.com :: Getting Started

I've received some emails about the ways to get started with RC Boats. This page will try to provide some answers and to give directions and how to tips for a successful beginning with radio controlled boats.

These advices are based on my own experiences and on information gathered around from people more knowledgeable than me.

First you have to consider a few issues like money, space to run the boats, environmental constraints and even size of the boats.

If we are talking about top notch competition boats the costs are big for any of the types, so you probably will have to decide based on the other criteria.

I try not to be biased towards any of the types, but I find the tweaking and tuning of an electric very appealing. However the 4 minute runs seem to be very small when compared with 10 to 15 minutes in nitro or even more with gas.

Electric may be simpler to start with if you don't have experience with nitro engines (these small devils can be very temperamental) or if you don't have the money to start with a complete gas boat.

Size counts also and with gas you may need to consider powerful servos and more expensive hardware than in smaller boats (electric and nitro) and this will had up to the final amount.

The sure thing is that you will surely want to progress in speed and technical sophistication and probably won't end up with just one type.

Monohulls have a single planning area. In some cases, like the Crackerbox, they have a flat bottom, but usually they have a V section hull with varying degrees.

The angle of the V is known as the "deadrise" and is directly related with the behavior of the hull on rough water. The flat bottom of a Crackerbox will slam in rough water, whereas a deep V will cut trough the waves and handle much better. A deadrise angle of 20º will result in a stable boat in the rough. This picture shows a scale stepped monohull of an offshore boat

In this picture you can see the steps on this hull. The idea of this design is to reduce the wetted area of the hull by creating a discontinued surface that helps reduce the wet area. (See below)

The bottom features two transverse steps. The first step set the angle of attack and guides the hull. The second step sets up the water flow for the last part of the hull which carries the load.

The goal is to minimize wetted area and planing resistance by causing the water not to touch the forward portion of the surface behind the step.

The steps suck in air and add it to the water under the boat, produce air bubbles like ball
bearings that will provide a faster surface for the boat to run on. Planing over a bed of foaming water means that friction is reduced.

Two step monohull for 7 cells surface drive. Lots of fine details and an excellent fiberglass hull. If you want to know more about it, I have one. Go to the detailed Targa page to know about it

This is one of the features you'll find on (almost) every hull whether it is full size or a model. The objective is to create directional stability and lift. Multi hulls (below) usually have special strakes pointing downwards so that the water can create a lift force to reduce boat drag.

Whereas normal spray rails deflects water horizontally away from the boat, creating friction and drag, the these special strakes deflect water downward to further enhance lift and speed.

This hull is a submerged drive "Multi". The V is shallow but much sharper close to the bow. They need good acceleration from rest and out of the corners, precise handling and a minimum of speed loss when turning. Their appearance is due to their function and they usually have a "self-righting" design.

These classes are very popular in Europe where you can see from the very sophisticated computer modeled designs, to the ones made with balsa and conventional building methods.

They derive from the Monohulls and in fact they have two hulls joined by a bridge section. The wet area is smaller and they ride on a cushion of air trapped under the bridge. The air supports the weight of the boat producing lift.

This makes this type of hull very sensible to water conditions and especially wind. If these two factors are not right the boat will blow over in beautiful aerobatic maneuvers.

They do not bank in the turns as a V would do, allowing much tighter turns. The dearise on the sponsons may vary between 0º and 17-20º. However the more deadrise it has, the better will behave in rough water conditions. The fastest examples may have at most 5 or 6º deadrise. The way these hulls behave is exactly the same as their full size counterparts. However there's nobody inside and this is wonderful if they blow over. The "rescue team" needs to be concerned with the boat alone :-)

These hulls take the principle of a reduced wet area to the extreme. They ride on three points - the sponsons and one point at the back, usually the propeller. They can be classified as scale Unlimited or a more functional Outrigger design. They can again be divided between those that "prop-ride" and those that rely on sponsons at the back or the hull.

The ones that "ride" on the prop use special design props that cause vertical lift. The thrust cone is much wider producing some down force that makes the hull go up. The propeller will serve two functions - Thrust and Lift.

The picture above depicts a modern scale Unlimited hydroplane, but some years ago the designs used were the famous shovelnose hydros. Here is one of those examples. There area couple of manufacturers that make these round nose hydros. The one in the photo is produced by Hydro & Marine, but Maus and Bandit Boats also have their own designs.

Sean Robson with his
Aveox powered Maus rigger
at the Canadian Nationals 1998.
(picture by RBW)

A type of hull that takes the principle of a purely functional approach, is the Outrigger design. They look like a fork, with a slim center section and two sponsons in the front. This is the fastest type of hull you can get. They are stable even when the water gets rougher and achieve incredible speeds.

The beauty of the hull it's another matter... You can always paint it with a nice color scheme. Anyway, the goal is to go fast and win the races.

Some have a pair of sponsons at the back of the hull to help stability, but others (like the one on the picture) rely on the prop to produce the necessary lift on the back of the hull.

The design I've made (XS) relies on this principle. If I need to put sponsons at the back it is fairly easy to do at a later stage.

There area few manufacturers that make good fast electric boats for starting. Here are a few links of places where you can get them

If your budget can accommodate a sophisticated boat then you can go a little bit further by upgrading some parts on your boat or even by getting a competition capable boat.
Either one of the manufacturers above have a complete range of boats and setups that fit your needs. The final choice will eventually be dictated by availability, looks or even results in competition.

Hull

All the hardware, including:
Motor, Motor mount, collet for connecting shaft to motor, shaft (rigid or flex), propeller strut, propeller, rudder and rudder mount.

Batteries and battery charger (see batteries) you if choose an electric.

Fuel tank, fuel filter, tubing, motor mount (eventually with rubber blocks), pipe (if you want that extra performance), starter field battery, glow starter (in case of glow engine), fuel pump.

Tools - screwdrivers, allen keys, cutting knife etc.

Radio - receiver, servos(s), speed control, antenna mount (optional)

This is another tricky question. A lot has been written about a good choice of motor but there's not a final word about this. There are a few types of motor that we can use

Ferrite motors - typically used in RC cars, best know as 500 motors. The magnets are ferrite and they exist with all sorts of winding combinations.
They use brushes (that need to be replaced with a certain frequency) and can have a variable number of windings of copper wire around the central element called the armature.

For instance a 17 turn double motor has 17 strands of 2 wires around the iron center.

This center is a stack of laminations in steel, which are pressed together to a length between 21.5 (minimum regulated size) and 22.5mm. For protection against damage and rust and prevention of the sharp edges cutting the wire while winding, the stack is hard coated (green or blue colored).

This part is called the armature.
As a general rule less windings have more rpms but less torque and more windings have more torque with less rpm.

On the following table you can see the relation between winding and the result in speed, energy and motor wear.

Turns	Speed	Energy	Motor wear
10
15
20

You can see the strands of copper wire, the central iron elements and the commutator plates in copper. On stock motors is supported by bushings but in modifieds it's usually mounted on ball bearings. Some care has to be taken with the motor or you will find a degradation in performance from run to run.

Keeping it clean with a special solvent to remove all the dust, should be done after each day of running. Then you have to oil the bearings (the motor makers also make a very thin oil for this purpose). The comm needs to be rectified now and then (depends on the wear) and the brushes and springs checked.

I've seen hard springs get soft due to the heat produced during a run. Then the performance of the motor dropped drastically and I only found the problem when I looked closely at the spring.

The choice of brushes and springs is also very important. When you buy a 540 motor they (normally) come with medium or soft springs and soft brushes.

The springs we use are made from steel and mostly color coated. The springs are available in various sizes and wire thickness. The most used spring tension is about 135 degrees and this size will fit most circumstances. Springs do look easy and not so important but they really are very important as the every spring fits a different brush and motor which are clearer in the next chart:

Type	RPM	Power	Torque	Stock	Modified	Comm wear

90º
115º
135º
150º
180º

The conclusion from this chart can be made, that with a 135 and 150 degree spring you will in 95% of the situations have the right spring. For the remaining 5% we have to fine tune the motor in combination with the brush compound and surface.

Because in boats we run at full throttle all the time, the needs are very different from the needs of a RC car motor. Strong springs and medium hard brushes will do the trick.

There are several types of brushes as you can see on any catalog and in this picture are the ones call serrated. To be honest I don't find that much difference between the serrated brushes and the normal ones. In fact after a couple of runs they stop being serrated due to the wear, so why buy them in the first place? Cooling? Here you have good explanation on why to choose a given type of brush.

Surface contact area / Face – The surface contact area is important in its way to have a maximum contact and so maximum power direct from the start. All manufacturers use the same brush surface radius to have an as good possible brush wrap around the collector. If there is too much difference between the radius of the comm and the radius of the brush, excessive arcing ( burning ) of the brush and commutator can occur, which will increase the damage and so the life of your motor.

If the commutator becomes to small, try too run in the brush slowly or use only serrated brushes, they will "break in" a lot quicker. Together with the compound the face is the most important part of the brush, as it makes the contact between the brush and the commutator.

The word tells enough, this means just the standard brush which most of us use. They are available in various compounds for all types of performance required.

With the maximum surface of the brush touching the comm this brush will definitive give us maximum punch , but also maximum current flow! And due to the full contact we can not expect increase of rpm also.

It’s sometimes a big increase in efficiency if the brush runs in during the race, it takes normally 3 minutes before the brush is bedded in.

In combination with the 135º-150º spring you will find the best balance between acceleration, rpm, efficiency and brush/comm life. This combination is ideal to save energy when we do not have the "efficient finger".

This brush is ideal to be used with very hard springs ( 180º ) in situations were extra acceleration is needed. Take care though of excessive brush and comm wear and a big increase in current flow, a good battery is needed!

This brush is not advisable to be used in combination with soft ( 90-115 ) springs, as brush bounce and sticking brushes can occur very easy. If RPM or efficiency is needed use another wind or change to cut brushes.

A cut brush is a narrowed full face brush, with the sides maximum narrowed 50%. Some manufacturers shave 25% of each side, this is done to stabilize the brush on the comm as the springs pressures in the middle.

Each percentage you shave of the sides, to a max. of 50%, will increase the rpm and decrease the current flow and acceleration. The trick is to shave of as much as possible without losing punch and will be the most easy obtained with the use of "power" brushes.

I strongly advice not to use hard ( 180º ) springs with cut brushes as these will damage very badly the comm. There will be over excessive brush and comm wear due to the high comm pressure.

With the use of soft ( 90º-115º ) springs, take care of the increased comm wear ( arcing ) with the use of high rpm winds.

In most situations the 135º-150º spring will work the best, use only the 150º in combination with a max 20% shaved brush. The brush shaved 10% will help drivers with a very punchy driving style who do not have the ability to save energy.

This is the latest revolution in brush technology. The added lines ( serration ) on the brush face increase the run in sequence as well it increases the efficiency. The big advantage is that no running in is required at all, which decreases the chance on having a "slow" motor. This brush is always the safest bet for the start.

The disadvantage though is that springs pressure is very important and that the motor will have a little less punch due to less contact area. Do not try to "cut" these type of brushes as the result will be a slow motor with a burned comm after the race. I think that is not what we want!

Hard springs ( 150+ ) are not advised as they will increase the serration wear, and we want to keep the serration lines as long as possible. We do not need hard springs as the brush pressure has been increased anyway due to the brush design.

A timed brush has been cut in a way to increase the timing. This has been done to increase the rpm and power in motors where you can not change the endbell timing, like stock motors. The brush has to be placed in the brush holder with the non cut part in the direction of the timing of that particular motor. Especially care has to be taken to slide the brushes at both sides the same way in the brush holder.

Timed brushes do have no use at all for motors with the possibility to time the endbell, as there is a reduced surface area, which will decrease the power.

Soft springs are not to be advised since the high arcing due to the high timing. Also there is already less surface area, a softer spring will make it only worse in contact.

Medium springs will work good, a 150 spring maybe used when high silver content brushes are being used to avoid brush bounce and arcing.

Hard springs will work fine to increase punch, but a big loss of rpm will occur!

Arcing: This means the sparking that will occur at the edges between the segments of the commutator, and burns the copper surface. It mostly happens with not proper cut comm, fresh brushes which are bedding in, soft springs and high timing situations. Also bad capacitors on the endbell do increase arcing, be sure to fit at least 2! Sometimes increasing spring tension will solve arcing also.

Brush bounce: Due to the wear of the comm and arcing the comm will become a little unround. If this happens due to high rpm and the springs used the brush will start "jumping" at a certain rhythm following the rpm. This is called brush bounce. It’s very normal it happens and happens more quickly with the use of power brushes which increase the comm wear. It’s easy to detect with holding a little screwdriver on the top of the brush while revving. If the screwdriver "jumps" the comm needs a skim. Harder springs also help but only increase the damage afterwards. Do not wait to long with cutting the comm as it the damage becomes worse and worse.

Brush wear indications: If you check the brush after each run you can learn a lot about the good or bad condition your motor is in. In general a brush that has changed color from new has been to hot. In most situations a too high load happened. The brush should always have the original color with a nice shiny surface. If the brush has not changed color but the surface looks black or a little burned you have to use a little harder spring for that motor. If you do not want that you have to make sure to clean the brush and comm regularly with a comm stick and motor spray to clean of the burned surface.

Also the brush length must be checked as a shorter brush will have less spring tension and so arcing and brush bounce problems will occur even quicker with a quickly increase of motor damage and decrease of power.

The commutator (copper plates where the brushes touch to make the commutation) wears out and it must be rectified for peak performance. Then you'll need a commutator lathe for keeping the commutators in good shape. Orion and Cobra make excellent lathes for around $150 USD. (see below).

The lathe is used to remove the grooves caused by the brushes friction against the commutator. With boats, we generally use strong springs and after a while the commutator wears off and has to be rectified, for optimal contact with the brushes.

While rotating on the lathe you can cut very fine layers of copper from the comm until the surface is even and polished. This will allow a perfect contact with a new set of brushes

Here you can see how a comm lathe looks like. The armature is set up on the lathe and driven by an electrical motor (usually a stock 540) connected to a 4 cell battery pack.

To get the most out of your lathe it's preferable to have a power supply, or else you will charge the pack time and time again. After a day at the lake (with several boats) you will have to rectify a couple of comms and you'll need a lot of run time on the power source.

You have the choice of diamond cutting bit or (a less expensive option) a carbide bit.
Let me just say that the finnish you get with the diamond bit is far superior. No micro grooves (yes, I've used a magnifying glass) and the bit lasts a lot longer if you take care. Cut little by little. Patience is a must.

Magnets in rare earths like samarium cobalt. More powerful, more efficient and more expensive than ferrite motors. They still use brushes that need to be replaced.

Special motor that do not use brushes and rely on special speed controllers to make the current switching. They are expensive, fast and the only thing that wears out are the bearings.

No need to clena the brush dust, or to check springs.
These motors have the copper wire windings on the can and the magnets on the rotating part of the motor - the armature.

Consider this - You have a really hot motor capable of delivering 40.000 rpm but with very low torque.
If this happens you would need a very small prop or you would load the motor too much. If the engine has a free rotation speed of 40.000 and with the prop you get 20.000, you are running it below the point of best efficiency and it may melt in a second. If you stall a motor the current can reach 200 Amps and melt the whole thing.
For avoiding this sort of problems and to get the best efficiency on a motor/prop combination you can use a gearbox. If geared at 2:1 a motor doing 40.000 would make a prop run at 20.000 rpm but with more torque allowing a bigger prop and much more efficiency. The motor would rev at the ideal rpm (if the ideal motor rpm was 40.000, more efficient = less current consumption) and a bigger prop gives better grip and less chance of cavitation. The best gearboxes around are the ones made by Hughey.

They exist for 2 motors or single motor and have the added benefit of multiple gear sets allowing a fine tuning for every gear/motor/prop combination.

The speed controller is a device that allows a smooth acceleration with an electric motor. If you only have a switch, the only thing you can get is on/off operation and you would not be able to control the speed in a way that you can do with an IC engine.

These ESC (as we call them) switch the current on and off so fast that it appears that the motor is increasing revs as a nitro engine would do.
The frequency at which the ESC does this contributes enormously to that smoothness of operation and also to a more efficient operation. When you see a ESC advertised as high frequency, this means that the ability to make that on/off sequence occurs for example at 2500 times per minute on a 2500Hz ESC.
Features like auto adjust, soft switch start and fail safe characteristics are some of the features you can get with some of these ESCs.

This is a feature that avoids having a separate battery for the radio system. Once the battery is plugged to the ESC this device has the ability to supply current to power the servos and receiver. Usually has a voltage cutoff threshold, so that the voltage is enough to power the radio system. Without this you could have radio control problems due to low voltage.

Some of these ESC's have a provision for water cooling. You you run it below max throttle, some of the energy is dissipated trough heat. If it builds up too much your ESC will be gone. It is one of the most expensive pieces you'll have inside the boat. Check if it runs too hot and then cool it the best way you can. I opted for water cooled ESC's, just in case.

You'll hear about things like BEC (Battery Eliminator Circuit) and this not mean that it eliminates your battery. It means that it eliminates the need for a separate battery for the radio system.

This is one of the most delicate areas one can write about. We are so used to have those batteries lying around the house on all sorts of devices, that we tend to look at them with a rather superficial attention. However, these batteries are one of the most important parts of an electric boat.

The batteries we use are usually NiCad, or to use the correct designation - Nickel Cadmium batteries. Recently another type appeared on the market - NiMh or Nickel Metal Hydride batteries.

They have to be special because they are subject to fast charges (up to 5 or 6 Amp) and to very fast discharges. Peaks of 70 Amp are perfectly plausible, but a more regular 20-30 Amp discharge is very normal. Manufacturers like Orion or Trinity sell special matched packs, in which all individual cells are tested under certain conditions and the ones that show similar values of running time, internal resistance, end voltage will be packed together to ensure that all elements in one pack behave the same way.

On his book Fast Electric Power Boats, Paul Williams says that after a while the cells stop being matched because with all the charges and discharges they will start to show very different behaviors, voltage and capacity. They need to be slow charged once in a while to put them all in a very similar state of charge and capacity. My personal testing showed this to be absolutely true. However these cells (matched) can accept more charge than the regular loose cells and this is mainly the reason why you pay that much for them.

You have to take care of your packs and cycle them every 5 or 6 runs, so that the risk of inverting a particular cell is minimized. And what's this inverting stuff?

Imagine that you have a 6 cell pack with a weak cell inside. When fully loaded 5 of the cells have a 1.45V, but one of them only reaches 1.25V. If you discharge it during a run, the cells may go as low as .9V, but the weak cell can go even lower, and this may cause the inversion in polarity of that cell.

The way to avoid this is to slow charge your pack (capacity of the pack/rate of charge * 1.4) every 5 or 6 runs, so that all the cells will attain the same voltage slowly. For instance a 2000mAh pack could be charged at 200mAh for 14 hours (2000/200*1.4) to achieve this. At this rate (C/10) even if you leave the pack charging for more time, no harm will be done. All the cells will be even at the end of the charge, and the chance of reversing polarity on a cell after a fast discharge is greatly reduced.

These tests were made in 3 packs (1 2000 mAh and 2 1700 mAh). The fisrt two packs show a very healthy state with 10% and 12% above nominal capacity, but the third shows a degradation indicating exhaustion. If a pack is below 95% it's nominal capacity it's gone! Notice that after 3 cycles the pack nº3 is regaining it's capacity. The charge made by the analyzer does not have peak detection. There's a chance that the 9 hours are not enough to fully load the pack.

In this activity, the packs are subject to very high rate discharges and this makes them special in several respects. When you buy a "regular" assembled car pack there are a few things that need to be changed.

First of all, the connectors are probably not suited to the type of use and the current involved. You'll need special connectors that can handle as much as 70 amps. The "Tamiya" style connectors will melt when used in boats. The resistance is too high and the heat produced destroys them. There are several types of connectors you can use, and personally I use Astro Flight connectors. They are low resistance gold plated and recommended by some of the world's top racers.

At the left you can see special connectors from Team Orion, able to withstand very high current.

But if you change the connectors there are still 2 major issues to solve : the wiring and the cell connectors.

We usually use 13-14 gauge silicone wire, multithreaded and low resistance. The major battery and motor manufacturers sell this type of wire and believe me, you'll need it. I've melted to "Tamiya" style connectors together and the complete wiring from the ESC to the motor on one of my boats.

The way batteries are assembled is also very important. The "regular" packs use metal tabs to connect the individual cells, and they are machine soldered in points (normally 2 or 4). The resistance of these tabs is too high for this use, and at high current they just turn blue from heat. Sometimes they can destroy the shrink wrap on the cells and ultimately destroy your pack. You can disassemble your packs and connect the batteries with special low resistance tabs that conduct the currents with minimal loss and without heat build up. The other way is to solder batteries together, but you'll need a special head for the soldering iron.

Bear in mind that when soldering cells all care must be taken in order not to heat the cells too much. Excessive heat may cause irreversible damage to the cells.

If you buy a boat for starting in this hobby, check the state of battery connectors and wiring after each run. If any of the components show signs of excessive heat, you may need to rethink the whole installation. A couples of hours and a few bucks can help you avoid problems when you need more speed and performance. Believe me - you'll want that extra speed...

Airage Publications has a site where you can get this book by ordering online. Press this picture to go there.

This is a fine book about Fast Electric RC boats. It's from Airage Publications and the author Jay Turner needs no introduction. There are a lot of tips and how to setup you boat.
It was written with the North Americam boating scene in mind. If you are from Europe and need a book more adapted to the European scene the one below is for you.

Anyway, the information about motors, hulls and batteries is wonderful. It was my first book and I've read it several times.