A BASIC GUIDE TO SUCCESSFUL
ELECTRIC FLIGHT

Arming Switch. A switch placed in the motor drive circuit for safety reasons, but a switch is so easily 'switched' accidentally that I would question their use. If a BEC switch or speed controller is being used then the arming switch should be placed between the controller and motor so that the motor alone can be isolated. A blade fuse mounted in a convenient position can double as an arming switch. This type of 'removable link' is inherently safer than a switch. Better to be in the habit of disconnecting the flight battery immediately on recovering the model after a landing.

BEFA British Electric Flight Association, yes as ever there is a national body to join but BEFA I think is worth your time and money. An A5 booklet is produced quarterly running to some 70 or so pages and containing much useful information for the sport and competition flyer, fly-in dates, etc. BEFA also organise an AGM worth attending (really) with lots of goodies for sale and even better is their Technical Workshop with traders, lectures and food. Current Membership secretary, Bob Mahoney, 123 Lane End Road, High Wycombe, Bucks. HP12 4HF If you are on the Internet the BEFA website address is http://www.ndirect.co.uk/~befa Or contact, Gordon Tarling, 87 Cowley Mill Road, Uxbridge, Middlesex. UB8 2QD.

Brake. A facility found on some electronic switches and speed controllers. When the electric motor is switched off the wind milling propeller and motor act as a dynamo. The voltage being produced is fed back into the motor via a connection made in the circuit, as this is of reverse polarity to the normally supplied voltage it produces a braking effect. When the motor slows sufficiently a folding propeller will fold back due to the airflow. A fixed propeller will not stop, it will continue to rotate slowly as the voltage produced and the related braking effect form a balance.

Brushless Motors. Although not new technology as far as industry usage is concerned these very efficient motors are relatively new to the world of electric flight. Most obviously, they have no brushes, hence there can be no sparking as caused by brushes and the need for suppressers is removed. They are also very efficient, ferrite versions are about 60% to 70% efficient, rare earth magnet versions (cobalt, neodym) up to 80%. Remember higher efficiency means more 'output' thrust for faster, better climbing models or longer flight times from the same 'input' power (battery).

The construction of a brushless motor is radically different from the standard DC permanent magnet motor that we all know and love. The most basic components have there positions reversed. The series of coils of wire normally found on the rotating 'rotor' shaft are instead formed around the inside of the case, making them the 'stator'. The magnets normally fitted to the inside of the case are instead spaced around the motor shaft and rotate (usually four magnets). As all of the electrics are on the outside as it were the need for a commutator and brushes to pass electrical current to rotating coils is removed.

BUT, and it is a big one. The commutator is a cheap and easy way to switch the polarity of the 'rotor' mounted coils (electro- magnets) as is necessary to cause a motor to rotate. The brushless motor does not have a commutator and brushes so this switching of polarity is done by an electronic controller. Suffice to say that it is a very complicated device beyond description here, even if I did understand it's workings. Complicated electronic devices are expensive and therefore so are brushless motors but electronic devices do tend to reduce in cost rather than increase. So, keep an eye on the advertisements, if you move on from the general fare of this booklet to larger more powerful motors then brushless is probably the way to go. Buggy/540 Motors. Hot stuff generally, in the early days of electric flight these were the motors to use, indeed little else was available. They could supply the power but because they were used direct drive before gearboxes were commonly available they ate amps at an alarming rate so flight times were disappointingly short. Today however we have learned to let them really howl (quietly) on a small propeller on a pylon racing type of model. Or to match the motor to a high ratio gearbox again allowing the motor to rev. fast while turning a usefully large propeller in an aerobatic model perhaps. 540 motors are often referred to as so many "wind" this is the number of turns of wire on each pole of the motor armature. The more winds, the thinner the wire, the less maximum amps the motor can consume, the less powerful the motor. The less winds, the thicker the wire, the more maximum amps the motor can consume, the more powerful the motor ('hotter'). Ducted fans are an ideal situation for the hot 540.

Charging Supply Battery. People do use their car battery to charge their flight batteries, this is not recommended particularly if you drive a modern car which may have microprocessors controlling various safety systems. Such microprocessors may be damaged by supplying power to your charger. Use a separate 12v battery fitted with some sort of carrying handle to ease lifting it. Heavy duty leisure batteries are often recommended but if you are using only 7 cell packs, particularly low capacity cells (700mAh - 1200mAh) a basic car battery is adequate for a full days flying. Top up the charge after each flying session to save it from being drained to too low a voltage and avoid damage. Car batteries are not designed to be deeply discharged before recharging but leisure batteries are, hence their recommendation for heavy duty use.

Cobalt Motors and other rare earth types. Cobalt, Neodym, etc. is the material that the magnets are made of. These types of magnets are much more powerful than the normal ferrite type. Also much more expensive. An advantage of these powerful magnets is that the motor can produce good torque at lower revolutions per minute than a ferrite and therefore turn a larger propeller without the use of a gearbox. Conversely, intelligent use of a good ferrite motor/gearbox combination can often produce similar thrust and hence, fly that model, at lower cost. In normal use it is very unlikely that you will ever wear out a cobalt motor as these magnets are generally only found in the best made motors.

Cooling. Cooling is recommended in all circumstances, particularly cooling of the motor and battery pack. The speed controller will usually benefit from cooling air too. A bluff nosed model can incorporate intake vents above or below the motor to good effect. On a sleek glider or racer with a close fitting spinner some form of scoop needs to be incorporated (facing forwards) or a NACA flush intake (posh name for a curvy triangle with one point facing forwards). An outlet is essential and can be incorporated behind the battery pack, perhaps just beyond the wing trailing edge in the upper or lower fuselage sheeting. Keep a clear path for the air and direct it if necessary with baffles.

A cooling tube with a fan at one end and open at the other is a useful field accessory, use it to cool flight batteries after use. A battery should be cooled to feel just warm rather than hot before it is put back on charge. Hence the often quoted need for three flight batteries per model, one 'flying' one 'cooling' one 'charging' for constant flying. But how do you then fit in talking? Two batteries will allow one 'flying', one 'charging', then the first battery 'cooling' whilst you're talking. Or better still take two models, one battery apiece.

End-To-End Soldering of battery packs. A method of constructing a battery pack where adjacent cells are soldered directly together without any form of connecting braid. The cells are placed in a jig (after tinning) and the positive and negative connections heated at the same time with a special 'hammer head' soldering iron. The iron is removed and the two cells pushed together. Braid or a connecting bar is still required at one end of a pack.

Flux Ring. An iron ring clipped around the motor casing. It's function is to bridge the gap between the two magnets inside of the casing. In most cases this has the effect of improving the efficiency of the motor, moving the maximum torque produced by the motor lower in the RPM range. To us slightly less power but a longer motor run drawing less amps. Or, as explained previously you can use a larger propeller to raise the amps to the previous level and produce more thrust.

Fly-ins. THE place to find out which combinations of model and equipment work and how. Look for dates in Electric Flight International magazine, BMFA News and the BEFA magazine. Meetings are reasonably well spread throughout the country and highly recommended.

Fuses. A minefield of opinion and confusion surrounds this simple device. Just what does it protect? "The crop in the field in which your model crashes", is my best answer. Considering how slowly (in electronic terms) and at what current the average 15 or 20amp fuse blows it is unlikely that it will protect the speed controller. But it will prevent a fire, and if only for that, is recommended. Mentioning the speed controller, many are thermally or fuse protected internally but that is no substitute for the main system fuse.

Fuse rating? 10 amp for 400 motors, 20 amp for 600 should allow normal operation yet blow should the worst happen. Experiment to find which is the smallest fuse that will stand the start up load, this is generally the highest current drawn during a flight. The most convenient type to use is the commonly available automotive blade fuse. It can be connected between two insulated spade connectors or slotted into a purpose made fuse holder, in-line types are available. Position the fuse between the motor and speed controller so that if you are using a BEC system and the fuse should blow power is maintained to the receiver.

Heat Shrink Tubing. As it's name suggests this tubing shrinks in diameter when heated, available in various diameters (un-shrunk) to insulate joints to connectors or hold together and protect complete battery packs. Tubing usually shrinks to half of its original size.

Installation. It is advised that a speed controller should be kept as far away as possible from the receiver in a model due to possible interference problems. Likewise, keep the receiver away from the drive motor. Having the speed controller alongside the motor is fine. So a logical layout from front to rear (or vice versa in a pusher model) is motor, speed controller, servos, receiver. Speed controllers are generally supplied with quite a long receiver connection lead to facilitate this. The drive battery should be positioned, if at all possible, so as to allow a clear exit without hitting anything expensive in the event of a crash. The inside of an electric model will have a tendency to become a 'rats nest' of wires. Route the servo and power wires in a logical fashion. The situation to avoid is that of connecting the drive battery into the wrong side (motor output) of the speed controller, exit speed controller. If two pin connectors are used such as the Mate-n-Lok they can be polarised such that it is not possible to make this mistake. With individual plugs and sockets extra care is needed.

When setting up a new radio control installation involving a BEC system do not connect the speed controller and motor initially. Test the servos by connecting a standard receiver battery and switch harness, when satisfied the receiver battery is disconnected and the speed controller and motor is connected to the receiver but do not fit a propeller yet, the speed controller can now be set up, starting/brake point etc. Some speed controllers have been found to work in the reverse direction to others in respect of the throttle stick position, you can imagine the mayhem produced if a propeller is fitted to the motor when you find this out. The solution to this reversal situation is simply to switch the throttle reversing switch, hopefully you have one. Also be aware that some speed controllers and switches can cause the propeller to kick as they are switched on or the battery is connected. Other speed controllers may start the motor if the receiver is 'on' but the transmitter is 'off'. To help to avoid these potential problems here is a recommended procedure for 'switch on'.

If using a BEC system.
a. Switch the Transmitter 'on'. Throttle stick in the 'off'/closed position.
b. Connect the flight battery to the aircraft system (speed controller).
c. Switch the receiver BEC supply switch 'on'.
d. If fitted, switch the arming switch 'on' just before launch.

If not using a BEC system.
a. Switch the Transmitter 'on'. Throttle stick in the 'off'/closed position.
b. Switch the receiver power supply 'on'.
c. Connect the flight battery to the aircraft system (speed controller).
d. If fitted switch the arming switch 'on' just before launch.

Lubrication. Motors. Some motors have ball races either end of the output shaft (armature) if not sealed these should be lubricated with a little Teflon or silicone grease. Plain bearing motors will benefit from the occasional application of a little light oil, 'sewing machine oil'. Just a spot on the outside shaft to bearing surface. Gearboxes. Gears should be lubricated regularly with a little Teflon or Silicone grease on the teeth. Metal to metal gears wear more quickly than plastic to metal, so inspect them regularly. Be sure that any grease used is compatible with plastic where plastic is present, even if it is only in the case. Gearbox shaft bearings are treated in the same way as motor bearings.

Motor Mounting. With their lack of vibration (if you balance the propeller) electric motors can be mounted very simply. All motor cases are provided with two tapped holes in the front face, a direct drive motor can be mounted on to a plywood nose former by these holes using appropriately sized machine screws. Alternatively a saddle can be made from short lengths of triangular balsa incorporating a couple of metal hooks, the motor can be held firmly by a rubber band or two stretched over it between the hooks. Gearboxes are sometimes provided with beam mounting lugs so that they can be mounted like an I/C engine. Also various commercial mounts can be bought to either beam or radially mount motors. Rubber bands, cable ties, 0.4mm plywood tubes, plastic tubes, even paper tubes for a friction fit, all can be pressed into service with a little ingenuity.

NICAD Cells. Nickel Cadmium, until recently the only choice for electric flight. Companies like Sanyo and Panasonic have developed these cells to their current level of efficiency at high current drain for the battery powered tools market. Happily they suit our purposes too, but there are problems particularly with disposal of the cadmium so manufacturers have been searching for a more environmentally friendly replacement.

NiMH Cells. Nickel Metal Hydride, the new kid on the block. Although cells of this construction have been available for many years only recently have they become available with fast charge and discharge properties suitable for our use. These are 'Third Generation' cells. These cells can be charged at 2x to 3x C rate (see earlier). Early tests indicate that below 20 amp discharge current the NiMH cells will give a longer motor run but at slightly less voltage than similar NICAD cells. Suggesting that the NiHM cells are better in these 'soft fly' situations. They will no doubt improve. NiMH cells are certainly a 'greener' option in that they do not use 'heavy metal' (cadmium) in their construction.

Opto-coupling. If you have ever gazed across a crowded room into the eyes of a beautiful member of the opposite sex you may think that you know what this means... but you would be wrong... very lucky, but wrong. Opto-coupling is a term used to describe a particular feature of some speed controllers. Principally the motor supply side of the circuit (which is liable to pick up 'spikes' of interference from the motor) is separated from the receiver (control) side of the circuit by the use of an optical link. Being an absolutely leak proof one way link this 'opto-coupler' protects the receiver from any on line interference from the motor. Unfortunately an inherent part of this isolation process is that a BEC supply to the receiver is not possible. Opto-coupling however tends to be available on the higher rated speed controllers for larger motors and models so this is rarely a problem in practice.

Ozone Layer. The slight sparking caused by the brushes running on the commutator of an electric motor produces ozone. Here is your chance to do more for the earth than just buy CFC free products. Fly as often as you can, for all our sakes.

Propellers. "If you don't have enough power to fly the model, fit a bigger prop." Unlike their I/C engined cousins this does work with electric power so long as the motor remains within it's safe operating current. Use your ammeter. An I/C engine, especially a two-stroke, if fitted with an over size propeller will slow, and produce less thrust for a longer time per c.c. of fuel. An electric motor in the same situation will draw more current and produce more thrust for a shorter time, draining the battery more quickly unless it burns out, it will really try. This difference in behaviour can be very confusing to the oily convertee.

Propellers designed for electric power are generally lighter, thinner and more efficient than internal combustion propellers and of course they can be of folding design. Some I/C propellers can however be used successfully for electric flight The choice of the correct propeller is far more important to successful electric flight than is the case with I/C power. A different make and shape of the same size propeller can make all the difference, be led by example but never be afraid to experiment. Buy or borrow lots of propellers around the size you require and try them. A pool of propellers among friends is a good idea, often a couple of flights is enough to tell you that the propeller is right or wrong for the model. Never try to use an electric propeller on in I/C engine.

Propeller Balancing. Unfortunately not all of the propellers and indeed spinners that you buy will be perfectly balanced. An out of balance propeller will cause vibration and a loss of power. Simple propeller balancing rigs can be bought quite cheaply. Or you can make your own if you have a straight piece of metal rod two or three inches long of sufficient diameter to be a snug fit in the propeller or propeller hub, and two empty wine glasses (over 18's only). Push the propeller on to the rod and attempt to balance it across the two wine glasses, this may be tricky if you have only recently emptied the glasses. If one blade of the propeller persistently swings down it is, unsurprisingly, heavier than the other. File a little material from the front (curved) surface at the tip of the heavy blade until the propeller balances. If you are balancing a folding propeller with a separate metal hub, first try swapping the blades on the hub as they may be better balanced that way around.

Spinners can be more difficult because they cannot be easily mounted in a balancing rig, they can be dynamically balanced however. Put your balanced propeller on the model, fit the spinner and run the motor, you will be able to feel any significant vibration, if not, all is well. If you do feel a vibration, first try turning the spinner though 180 degrees, if this is no better stick a small 1cm square of insulation tape to one side of the spinner between the blades, try again. If the vibration is a little less add a little more tape, if it is worse move the tape to the other side. When all is running smoothly remove the spinner and trim a little material from the inside edge of the spinner at the opposite side to the tape, remove the tape and run again, do not remove too much material at a time or you could reverse the problem and get really confused. When you have a well balanced set-up mark the propeller, hub, and both spinner parts so that they can always be fitted the same way around. While all this is happening, check that the spinner is running true. If the tip of the spinner looks blurred, it's seating needs attention.

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