Reproduced by Kind Permission of Nigel Hawes and RCM&E
STILL CONSIDERING HAVING A GO AT ELECTRIC FLIGHT BUT DON’T KNOW WHERE TO START? NIGEL HAWES THINKS ITS TIME YOU JOINED IN THE FUN! HERE HE EXPLAINS IN LAYMAN’S TERMS WHERE TO START AND WHAT’S INVOLVED.
When you do something all the time, it soon becomes second nature, and you tend to take it for granted! When I was 20 and my friends were going swimming, they didn’t know whether to be horrified or amused that I couldn’t swim; the reason being that I missed out on swimming lessons whilst at school and after that I thought I’d left it too late to learn!
Electric Flight seems to hold a similar parallel, when you look around everyone seems to be having great fun and success with it these days, but the feeling is there that you may have missed the boat.
Well let me assure you, NOBODY has missed any boat, and in fact the boat has changed course considerably and is now even easier to get on! The fact is that Electric Flight has finally come of age, and is both accessible and affordable - it’s just a case of easing yourself into it at the level you wish to participate, and hopefully this article might help to point you in the right direction for achieving success first time, on a comfortably low budget.
WHERE TO START?
Looking through articles and adverts you may think Electric Flight is a minefield of motors, Speed Controllers, Flight Batteries and chargers etc., but in fact all you have to do is look at it a slightly different way and it all becomes clear and falls into place.
For the dubious, there are plenty of tried and tested packages that will literally work straight out of the box; for the slightly more adventurous there is an almost foolproof formula you can follow that will work on any Electric model or even i.c.-to-Electric conversions!
Deciding where you want to start in Electric Flight is the first thing you have to do, after that it’s just a matter of making the correct and well - informed purchase decisions. But whichever level you wish to enter, it will help to know just a little about what makes an Electric model tick and the difference between some of the major components, so I’ll start the journey here.
In Electric Flight there are two basic types of motor; Brushed motors (i.e. those with a commutator and brushes) and Brushless motors (sometimes described as 3-phase motors).
Some would tell you that Brushed motors are becoming obsolete due to the incredible progress and cost-reduction of Brushless motors over the past few years; the fact is, you can still buy 400-size Brushed motors for around £5, and 480-size for only a small amount more, and yet they are perfectly capable of propelling decent size models with reasonable efficiency and longevity! So in my opinion they are still a very cost-effective way of dabbling in Electric Flight to see if you like it.
Legendary models such as the Multiplex TWINSTAR and TWINJET use pairs of 400 and 480 motors respectively, and I don’t ever remember anyone being disappointed with their performance or duration! So don’t be told you have to start up in Electric Flight by going straight into Brushless motors and their complex Speed Controllers, there is plenty of simple fun to be had with the good old Brushed can motors for many moons yet.
Indeed, as you can see from the picture, I fitted FOUR of the cheapest 400-size motors (costing £4 each) to an everyday Cambria Capstan glider, and the results were not only beyond belief using a basic 8-cell Flight Battery and cheap Speed Controller, but everywhere I fly it, heads are turned simply because it is so unusual! Once you find your feet you can experiment with all sorts of different configurations with surprising results.
THE “BRUSHLESS REVOLUTION”.
Brushless motors have come down considerably in price in the last few years, particularly OUTRUNNER types which are easier and cheaper to produce than the more conventional looking Brushless can motors. On an Outrunner type motor, the entire can containing the magnets rotates around the stator of coils (arranged a bit like a radial engine as you can see in the photo) - this gives the motor a great deal of torque and this allows what look like quite small motors to turn disproportionately large propellers.
From an i.c. flyer’s point of view, this would be a bit like taking the 7 x 4 prop off your OS.10FP engine and replacing it with a 10 x 6 - of course this wouldn’t work; but with Electric motors, particularly Brushless Outrunner motors, it can work as long as the correct Flight Battery is used.
Naturally the Speed Controller for a Brushless motor is far more sophisticated, as it has to effectively change the simple Direct Current supplied by a battery into extremely complex 3-phase pulsed Alternating Current, taking into account feedback and commutation levels that even I can’t even contemplate! What is probably the most amazing thing is that they are now mass-produced in such numbers that they have become in some cases even CHEAPER than the established, simple Brushed Speed Controllers of the past.
This has meant that while a few years ago a Brushless motor and controller would have cost you anything up to three or four times as much as a Brushed equivalent, the price difference is now far less significant and this may explain why even complete newcomers are drawn in to Electric Flight using Brushless from the outset; and there is nothing wrong with this at all providing you get a motor, Speed Controller, Prop and Flight Battery that are all compatible with each other.
The advantage with Brushless motors is that as there are no “frictional” parts (for example the piston and liner in an i.c. engine or the brushes and commutator in a Brushed motor), there is literally NOTHING that can wear out except for the bearings which should last a long, long time and in any case are often replaceable.
In all the time I have operated Brushless motors I have personally never worn out a bearing or heard of anyone managing it, so as long as you don’t overheat or crash damage a Brushless motor you can more or less say it will “last forever”.
Inevitably battery technology improves with time and we have seen several significant changes of technology that have furthered the case for Electric Flight. Initially NiCad (Nickel Cadmium) rechargeable cells were the mainstay of Electric Flight but as they contain some very unfriendly “heavy metals” that are harmful to the environment, these were effectively replaced by NiMh cells (Nickel Metal Hydride) which not only had the benefit of increased capacity per cell weight, but are also much friendlier to the environment.
Initially, they were of pretty mediocre performance but as with any type of technology, this improved with development and within a few years NiMh cells were actually not only higher in capacity but also as powerful if not better than the best NiCads of the previous era.
Probably the best example of NiMh technology is the excellent 3800 ma/h INTELLECT cell, which not only produces more than enough power for most Electric Flight applications, but is the first SUB-C cell that I have tested that can give a GENUINE 4,000 ma/h capacity.
This is a significant landmark, but does raise the question of just how far this type of technology can go, i.e. how big a capacity the SUB-C cell can give at the extent of its development. That said, for those unwilling to use Li-Pos, they are ideal.
THE LI-PO REVOLUTION.
Lithium Polymer batteries appeared on the market relatively recently and once again originated from the mobile communications industry; don’t ever kid yourself that we get batteries developed specially for our models!
Lithium as a useful element first appeared in Lithium Ion (Li-Ion) cells and apart from the extended length, looked pretty similar to NiMhs in that they were built into a metal canister. However when the soft “sachet” type Li-Po cells appeared and subsequently enjoyed an incredible pace of development, they soon changed the whole face of Electric Flight due to their tremendous capacity per weight benefits over previous Flight Batteries, and not only made established Electric models perform better but also allowed previously impractical i.c. to Electric conversions possible.
To give you an example, a 3300 ma/h NiMh 10-cell pack weighs almost three times as much as a similar capacity and power 3300 ma/h Li-Po; or if you want to increase duration rather than save weight, you will pack around 8,000 ma/h of Li-Pos into a model for the same weight as the 3300 ma/h NiMhs.
Put that way, it becomes extremely clear why Li-Pos have become the “must-have” Electric Flight battery and naturally as they become more mass-produced, they are not only becoming cheaper but better due to the intense development they are enjoying.
However, every rose has its thorn and Li-Po cells require far more attention than NiMhs. For a start, whilst we could overcharge, over-discharge and in most cases crash our NiMh packs in a model and usually get away with it, Li-Pos are much less tolerant to abuse!
Each Lithium Polymer cell has a nominal voltage of 3.7v, and a fully charged voltage of 4.2v, compared with a NiMh’s nominal 1.2v and charged 1.4v. This actually works quite well for us in that a 2S Li-Po (i.e. two cells in series) gives a similar voltage, especially under load, as a 7-cell NiMh and a 3S Li-Po is similar to a 9 or 10 cell NiMh.
However, you must NOT over-discharge Li-Po cells because if any cell in a pack is allowed to drop below 2.5v, it will not recover and becomes a “useless” cell. If this happens in a large pack of many cells in parallel or series, then the entire pack may be rendered useless as the cells require specialist soldering equipment and techniques to fit and remove, something no-one without such means must ever attempt.
Worse still, Li-Pos must NEVER be over-charged. If any cell is charged to even 5.5 volts (not that much higher that the 4.2v limit) it can go into a “thermal runaway” situation resulting in a short duration but incredibly fierce flash fire. I don’t want to sensationalise the potential dangers of Li-Pos, as ANY high discharge energy storage device has its potential dangers - but if you look at the pictures, and especially the short video clip of a Li-Po going up at http://www.bvrkits.com it might encourage you to be very careful with your packs!
Fortunately, the overcharging and over-discharging problems have been more or less taken care of by ESCs that stop the motor before the cells become over-discharged and specific Li-Po chargers that stop charging when the cells are fully charged.
In use, as long as you don’t try to draw more current from a Li-Po than it can supply (denoted by the “C” rating) they can be perfectly manageable and reliable with a good service life - but remember they will NOT take any abuse and should be arranged in the model with plenty of foam packaging as without a strong metal canister around them they are far more susceptible to crash damage! If a LiPo cell becomes distorted or crushed in a sharp arrival, nine times out of ten it will be irrevocably damaged.
These are often known as the ESC or Electronic Speed Controller. This clever bit of micro electronics basically gives your Electric motor, whether it be Brushed or Brushless, the same proportional throttle control as the servo connected to an i.c. engine carburettor. The difference is, you can completely stop an electric motor in flight, enjoy the glide for a while, then start the motor again with the throttle stick; there are very few i.c. models you can do that with!
Naturally, the ESC does FAR more than this. It has a function called B.E.C. (Battery Eliminator Circuit) that “siphons” off about 5 volts to supply the RX and servos with power from the Flight Battery, so you don’t have the added weight or inconvenience of having to charge a separate RX battery.
It also has a Power Cut-Off or “P.C.O.” function (far too often wrongly referred to as the B.E,C,) which stops the power to the motor when the battery nears exhaustion, prioritising the power to the RX and servos so you still have control. This PCO function is essential with Li-Pos as it makes sure you don’t over-discharge them below their critical voltage as explained above.
Many ESCs are programmable, allowing you to optimise switching frequency, motor timing for different types of motor, set the brake on or off, select hard or soft start etc., but if you are just starting in Electric Flight most of them have a foolproof and sensible default setting so despite the manufacturers’ efforts to make them extremely versatile, most of us just “plug and play” and therefore won’t ever need or use these functions!
Thanks again to mass production and rapid development, ESCs are very reasonably priced for what they do, and Brushless units are in some cases just as cheap or even cheaper than Brushed units, which clearly shows which way the market is going.
Given the diversity of cells we have in R/C modelling from NiCads to NiMhs, Li-Ion to Li-Po and even 2v and 12 lead-acid batteries used by i.c. flyers, chargers have to be pretty versatile units in order to cope with our demands!
Fortunately the market is brimming with excellent, reliable chargers that won’t break the bank, and I would urge anyone starting out in the hobby to shamelessly buy the best charger they can afford from the outset.
£50 will buy you a very good charger indeed; the one pictured here does everything I need in my everyday pursuit of Electric Flight and is available in various different guises.
Most are designed to work from a 12v car battery at the flying field but if doing a lot of charging in one session it’s always a good idea to make sure your car battery is in good condition!
For home charging, a simple regulated power supply such as the J. Perkins unit shown in the picture is ideal as long as you’re not running several chargers at the same time! Remember if you are giving a 5-Amp charge to a Flight Battery the charge itself will probably be drawing 7 or 8 Amps from its power source - something that is often overlooked!
A final note on Li-Po charging; ALWAYS where possible charge them using the separate plug connected to an “individual cell charger” or “balancer”, especially if the pack is well into its cycle life. These chargers ensure that each cell will never exceed 4.2 volts during charging. If you charge a Li-Po in series, as we have always charged NiCads and NiMhs, if there is a cell in even a 3S pack that has just “died”, the charger will still attempt to raise the pack voltage to 12,6v and this may risk overcharging the two healthy cells.
CHOOSING A MODEL!
Ok, we have looked at the individual items that make up our Powertrain, now we need something to put them in!
Model choice has never been wider when it comes to Electric Flight as we now have the power-to-weight ratio to succeed with more or less ANY project, whether it is a specific Electric design or an i.c. to Electric conversion. The limiting factor, rather than being “will it fly” has become “how much am I prepared to spend to make it fly!” - it is as simple as that.
As well as an almost infinite range of available plans (there are some excellent designs in the RCME plans service so have a look!) and kits on the shelves of every model shop, the market is now being completely flooded with ARTF (Almost Ready To Fly) offerings which in the main come from the far east and in some cases they come complete with the motor, battery and even radio gear!
Whilst this has almost brought entry level Electric Flight down to “toy shop” shelves, there are some particularly nasty ARTFs out there that have dubious equipment installed, all made to a cost so they are an attractive impulse buy.
I would advise that before rushing out and buying something like this, read the popular press and especially try to track down a review of the model; as well as frequent RCM&E reviews there is a gold mine of info to be found on the R/C forums and discussion groups on the Internet. A bit of research can save a LOT of disappointment!
Most specific Electric designs have been well tried and tested and the recommended motor, Flight Battery, ESC and prop size is all there for you. But when taking a step into the unknown, the numbers sometimes don’t add up!
The question I am most often asked by newcomers to Electric Flight is “what motor and battery is equivalent to a .25 i.c. engine (for example). And the answer I give is that ELECTRIC MOTORS AREN’T THAT LIMITED!
I have a motor and battery set-up that will give the equivalent power of a .10, a .15, a .20, a .25, a .30, a .35 and even a .40 i.c. engine, simply depending on how many cells and what size of propeller I use. In this respect Electric Flight is so much easier to master - it’s just a simple case of maths.
Believe me, it took me several years to finally grasp this aspect of Electric Flight but since then I have found it to work every time.
Power is expressed as WATTS, and this is the simplest calculation possible, i.e. the number of volts your battery is showing under load, multiplied by the number of Amps the set-up is drawing. Simply by plugging a measuring device such as a Wattsmeter into the circuit as shown, will tell you not only how many watts are being consumed but is an INSTANT indication as to whether you are over-Amping either the motor or Flight Battery; something you NEED to know!
As a basic rule of thumb, most models will fly on 50 watts per pound of weight. Make this 75 watts per pound of weight and you will have pretty decent performance. Stretch it to 100+ watts per pound and you will have outstanding, and in some cases unlimited vertical performance.
So for example, if you have a sport model that weighs somewhere between 4 and 5 pounds, for decent performance you will need a 300 watt set-up and to make it really perform aim for 500 watts; remember if you have more power than you need you don’t necessarily have to use it all!
On smaller models it is much easier and a lot cheaper to make them sparkle, for example a 2 pound model with a 200-watt 400-size Brushless set-up that doesn’t cost very much at all will eat up the sky like you have never seen!
In this case a 2000 ma/h 3S Li-Po (showing 10 volts under load) drawing 20 Amps (if it is a 10C pack) would be ideal; 10v x 20A = 200 watts.
BUYING A SET-UP.
Knowing this fool-proof formula will instantly relieve you of the confusion that goes with the ridiculous bombardment of numbers that afflict Electric Flight components. Coming from an i.c. background, whilst Irvine .46 might mean something to you, it is unlikely that 3630/1000 or 16/15/4 will be of any meaning at all!
However, contact a leading Electric Flight expert and ask for a “200 watt Electric Flight set-up” and that’s exactly what you will get, with each component of the powertrain (INCLUDING the correct prop size which is so critical in Electric Flight) being matched to each other and working within their limits so nothing is going to catch fire or melt.
Once you realise that the actual numbers themselves are of less importance than the wattage of set-up you require, Electric Flight becomes easy! All you need to do, for example when choosing a 300-watt set-up for a 3-4 pound model, is to make sure the Motor, Flight Battery and ESC are all up to the 300 watts you will demand, and that the prop size is correct.
The only thing I would say in addition to this is that some models require a small fast-spinning propeller (such as a fast pylon type) and some require a larger, slower-turning propeller (such as a powered glider or scale model) and 300 watts can be used in either circumstance simply by correct motor Kv and prop selection - but this is best left to the expertise and experience of the specialist you buy from.
I hope this has in some small way given some clarity to what can be a minefield of numbers and sometimes conflicting information! You CAN participate in Electric Flight the easy way, i.e. by following tried and tested set-ups and the simple fool-proof formula given above, making sure you buy your equipment from an experienced and reputable specialist who will give you the correct advice and appropriate gear!
Or you can, like I did at first, bungle from one frustrating failure to the next without really knowing what you are doing and wasting a lot of time, effort and money in the process!
Electric Flight is not only easier to succeed with than ever before, it is also cheaper and more accessible than we could possibly have imagined even a few years ago.
Every month I write the FLY ELECTRIC column in RCM&E to help identify good, cheap products that work well, and I review a multitude of suitable models along the way. If you think the time is right for you to have your first plunge into Electric Flight there has certainly never been an easier or cheaper time to do it so come on, join the fray!
There is a lot of cheap, quiet, clean fun to be had and with publications such as RCM&E giving constant product awareness and support if you’re having problems, you simply can’t fail to enjoy this fast-growing and exciting area of R/C model flying.