Peter Beeney

I would consider that a 3 phase synchronous motor is a motor supplied by a 3 phase AC supply. It simply synchronises to it’s supply frequency. The first thing that Luke Warm says, and I quote, - ‘The ESC controls the speed of an AC motor with frequency, not voltage.’ He then goes on to state, and again quote - ‘The speed of the motor has nothing to do with voltage or amps, but instead the timing of the current fed into it.’ Nothing to do with voltage or amps, apparently, but the timing of the current… So what is the current if not amps… And finally - 'RPMs: An AC motor's ESC controls the speed (RPMs) of the motor by changing the frequency of the 3-phase trapezoidal waves; the higher the frequency, the faster the prop will turn.' The ESC is 6 switches arranged in a half H bridge format simply to act as the commutator for the motor. Exactly as the mechanical comm. of a brushed motor. The speed controller, or throttle stick, does not change the frequency of this switching, this is controlled entirely by the speed of the motor. The speed of the motor is controlled by the applied voltage and the load; and the throttle stick does this by varying the applied voltage. One way of perhaps indicating this is in my statement - ‘If the kV is 1000 then 10 volts applied = 10,000 rpm, 20 volts applied = 20,000 rpm for an unloaded motor.’ Of course, the comm. switching is also going twice as fast at 20,000 rpm, but it’s driven entirely by the motor, all we’ve done is to double the voltage, we’ve done nothing to the frequency. I may have got this wrong, but anyone with a tacho and a couple of batteries can very easily do this simple test to prove it for themselves, one way or the other. Certainly an increased load will cause a larger effective voltage across the windings, but this is just Ohms Law again. Higher voltage = increased current = stronger magnetic field = more torque. Increasing the PWM duty cycle will surely only increase the voltage but also the speed, so higher voltage = etc. etc. But actually all we want to do is to control the speed, so it’s rather defeating the object. Maybe if we wanted the esc to act as a governor control to maintain a steady rpm under varying load conditions then I’m sure it’s possible there would be a need to vary the duty cycle automatically, but I’ve never seen this required by modellers; fixed wing anyway My overall view goes something like this. When the motor is at full throttle there are no PWM pulses, just the full voltage applied in a series of pulses of fixed duration to give the motor it’s turning motion. When the throttle is operated a PWM signal is sent to these main pluses, which are still of the same fixed duration, but it breaks them up into much smaller pulses, but still each with it’s fixed time period. If within each time period the voltage is switched fully on for half the time and fully off for the other half of the time the average voltage over the whole time period will be half the full voltage. Thus it follows, surely, that if nothing changes the applied (average) voltage over the full duration pulse will simply be half the full voltage. And the motor will run at half speed. Each fully switched on period, the duty cycle, I believe, is at the full voltage and thus the full current and torque, so power is maintained to a large extent. If the duty cycle were reduced to say 25% then it follows that the average voltage will be 25%, or one quarter. Motor will turn at one quarter speed. I don’t really think I can say very much more, except that, as always, we will each take our different views and go our own ways. And, as always, it probably won’t make that much difference in the end anyway… PB

Dave, Taking a quick look at that new link, I’m afraid I have to say again that I’m not at all convinced. About the only thing that I’d consider that does make some sense is that fact that he says, perhaps quite remarkably under the circumstances, that the current in the stator is AC. That’s a definite fact. But I’m sure there are very convincing arguments as to why some of the other stuff is a bit questionable, to say the very least. It would appear, then, that even his moniker, Luke Warm, is a bit generous, too… PB

I think your link just takes you to a speed controller for brushed motors, Dave, but it does at least talk a bit about PWM. Some of this causes me some head scratching anyway, but it does mention the capacitors across the terminals of brushed motors etc, plus a fast acting Schottky diode across either the motor windings or the transistor, I guess for the same reason that I mentioned for the relay. But as you say, perhaps not the time and place for this, maybe what it really needs is a general electrical thread where the subject and posts can wander about at will without causing any concern about going off topic. PB

Thanks for your reply. Actually,I was considering whether to mention the fact that the switching might have other effects, but I thought it might just clog up the issue somewhat. Yes, I believe the FETS on the esc have a diode built in which prevent the induced voltage from the winding from building up and thus preventing any unwanted voltages and currents being able to cause any mischief. I would think this is a bit like the reversed biased diode placed across a relay coil, for the same reason. When the current stops flowing the rapidly collapsing magnetic field creates a rising voltage within the windings, but because of the direction in which this is happening the diode now becomes forward biased and start to conduct. The diode is a low resistance path and it now very effectively shorts out the coil across itself. I’d have though this is of very short duration and not really enough of anything to have any reactions on anything else. The brushed motors of the past had capacitors across the windings and to ground for exactly the same reasons, to prevent the arcing and sparking at the mechanical contacts between the carbon brushes and the copper commutator segments as the armature revolved. With many windings, a fast switch off and high DC resistance the circuit without a diode might enable the voltage to get quite high on the relay coil, but would that be the same for a motor winding? Maybe the motor is different, but I was only trying to describe pulse width modulation as I see it, in very simple terms. That how I see everything anyway, I can’t do complicated. I’m now not even sure if we switch the voltage (and current) or the current (and voltage) or just simply ‘the electricity’ even, I’m afraid you’ll just have to bear with me on this one. Humble apologies if this post has now gone far off topic… PB

Exactly so, Dave, surely when the voltage is switched off the current then ceases to flow? So then I’d consider that when the voltage is switched off the lack of current ceases to create a magnetic field and the motor’s speed reacts to this; therefore depending on what the on/off ratio is, the motor will just go faster or slower. That’s how I see it, anyway. PB

With the greatest respect, of course, but taking another sideways view of all this, as always, I think the speed of the motor may depend on variously the strength of the magnetic fields, the number of poles and windings etc., but most importantly perhaps, the size of the load and the applied voltage. If the kV is 1000 then 10 volts applied = 10,000 rpm, 20 volts applied = 20,000 rpm for an unloaded motor. The esc is an integral part of the motor, the motor drives the esc and in turn the esc drives the motor. Neither will function without the other. In my lowly opinion it’s slightly misnamed too, I’d prefer Electronic Switching Commutator, the speed control bit is only really an add-on here. The motor would certainly not function without the commutator gizmo; but it doesn’t have to have the speed controller. If a motor is running at a steady speed with a given load and voltage and we then increase the load the motor will slow down by an exact proportional amount to that added load and the current flow will go up by an equal and exact proportional amount. These are all inexorably bound together. Add more load and the same thing happens, by an exact proportional amount again. Eventually, though, things would start to overheat due to the excessive current. Now if our motor is back at it’s steady speed and we wish to change this by some amount then we just change the applied voltage, the motor will respond accordingly. The speed controller circuit does not control any of the drive pluses in speed or overall length, the pulse switching speed is controlled by the motor and the length of pulse, in degrees, stays the same throughout; it simply switches the current on and off a number of times during each pulse to supply an average voltage, higher or lower, and thus current, to the motor. One of the feature that really sorts the men from the boys in terms of power trains is it’s overall resistance. The lower the better and we know model power trains do have a reasonably low resistance, so any increase can make quite a difference, percentage wise. If the resistance is say 100 milliohms and the current 50 amps then doubling to 200 milliohms will reduce the the current to 25 amps. For the same applied voltage. Could it be then that maybe Percy’s OP is just a case of some unwanted resistance somewhere? Unlikely, I expect, but in any case I’d certainly agree with PatMc, a quick call to the supplier might the best all round solution anyway. PB

John, Don’t worry about running these cell down to flat. They are stored for longer periods in a fully discharged state, often with a short across the terminals to stop any local action. But as I’m sure you can appreciate they might then need a good kick-start to get going again. Generally speaking, if a nickel cell is good it’s very difficult indeed to break it; and if it’s bad it’s very unlikely, (impossible) that you’d be able to repair it… PB

JB, I’m sure your battery will ultimately be absolutely fine, but if it were mine I’d consider that it was imperative that I test discharged it first. I’m sure your Ultramat will do this ok. This has been an ongoing problem for many years now, I’ve posted about it in various threads in the past and I’ve also written factual letters to a variety of suppliers and the BMFA; needless to say, I’m still waiting for an answer… Although, again as I’ve said before, an answer would prove that they’d actually received it and then in the event of an incident they might be asked some awkward questions. From my deductions over the years I think that when these new packs hang around for a while they get a bit lethargic and the internal resistance goes up a bit; this then becomes a bit of a hurdle for the charger to overcome. Particularly the Futaba wall-socket type. It’s definitely resulted in packs receiving little or no charge at all, thus an instant flat battery and very soon after a splintered model! I know this for at least one fact, it happened to me, I was test flying an immaculate brand new Flair Magnatilla for a club member, he’d assured me at least three times that the battery had been on charge all night, and when after about five minutes flying it was lying in ruins he told me it was a brand new pack! When it comes to power supplies I now never ever assume anything… Discharge your pack, at about 1 amp, say, to save time, ignore this capacity reading because it might be quite low, recharge, discharge and repeat until you are getting at least close to 2300Ah; it will get there. It’s possible to find a duff new park, I’ve seen about 3 in a lifetimes flying, but it is rare. I always used homemade nickel packs, (although now LiFe) for years, 5 cell Uniross 800mAh, for lightness. I charged them using a Schulze charger on auto setting; this took a half an hour from flat to full, the charge rate would start slowly, increase to up to several amps and then taper off. The pack never even got warm. They lasted for years doing it like this. For safety reasons probably the most positive recommendation in our club is the use of an on-board battery voltage monitor. I’ve checked a number of these and they are surprisingly accurate. Modern kit is easy to make cheap and precise! The use of these has stopped two certain crashes in just our small gathering, once particularly when someone spotted a glowing red led deep in the cockpit of a large Pitts just as the pilot was starting the engine!! Good maintenance and regular checking will ensure trouble free power supplies. Without power everything else is just useless… Once your pack gets in the swing of things the wall-socket will charge it, albeit slowly. On 5 cells the output will probably be less than 50mA, I’ve tried it, so a standard charge, 150% of capacity, will be 3450 divided by 50 = 69 hours. You could leave it on indefinitely. The voltage comes up straightaway, which is why the led dims and never try to check the state of a nickel pack by simply reading just the open circuit voltage. It could be a disaster… Good Luck. PS Addendum   JB,  One way to check the pack is fully charged is to discharge it and make sure you put virtually 2300mAh back in. But the on board monitor does run it a very close second…     Your charger will discharge a NiMh down to 1 volt per cell - 5 volts. Don’t worry about any individual cells, the charging regime sorts all that out. For nickel, that is.    PB   Edited By Peter Beeney on 17/05/2016 14:09:12 Edited By Peter Beeney on 17/05/2016 14:15:42 Edited By Peter Beeney on 17/05/2016 14:21:38

Is it worth just slipping the esc throttle lead into a spare channel, for power, and a servo into the throttle channel? This at least will visually prove full stick movement or otherwise. If ok, then extend the throttle travel beyond 100% in the tx and see if that has any effect… …or perhaps even reduce it, cannot do any harm. However, when I’ve pottered around with this in the past I did find that going too far over the top made the esc shut down altogether! Only just a thought… PB

Thanks for the reply, Rob, and apologies for adding one last post. I also forgot to mention that in this case HV = High Voltage - although that is pretty obvious, I suppose… It’s always going to be logical to label any electrical component with the working voltage that it’s designed for, but it will also be able to accept the range of voltage that it’s supply can cover. In the case of the lipo that about as simple as it gets, 3 to 4.2 volts per cell. The nominal voltage of 3.7 volts/cell was originally 3.6, the mid point between 3 and 4.2, this will be the average voltage of the cell as it discharges from fully charged down to completely discharged. Then someone thought they might be able to claim a bit more performance over the opposition by upping to 3.7. Everyone else then naturally enough followed suit and it stuck. The capacity of a cell is usually quoted in ampere hours, Ah, but there is an alternative way which is watt hours, Wh, (or maybe minutes, or seconds,); but to do this we need a voltage as watts are amps multiplied by volts. We can only sensibly use the average voltage because anything would give us an incorrect value. Looking at a single cell, say, a 1000mAh 3.7 would be 1Ah x 3.7V = 3.7 watt hours, 2S would equal 7.4 watt hours. This is useful if we want to compare it with a different type of cell, let’s say a NiMH. Again the capacity is 1Ah but the average voltage is only 1.2 so the Wh capacity is only 1.2 watt hours. So we need 3 NiMHs to 1 lipo. for the same amount of Wh capacity. It’s also another means of checking the flying time of electric models. Our model has 100 watts reading on the wattmeter and we are using a 2200mAh 3s pack. So 2.2Ah x 11.1V = 24.42Wh. Divide by 100 = 0.2442 hours. Multiply by 60 to convert to minutes = 14.652, and 0.652 by 60 again for seconds = 40. So a total flying time of 14 minutes 40 seconds on a constant full throttle. It doesn’t really matter much how you do this little calculation either, but it’s necessary at some point to make the units the same value to give the answer conveniently in minutes. And this is only very much an approximation anyway, trial and error using the throttle will soon prove to be more accurate. Hope this might of some interest and assistance to someone… PB

Rob, If I were using these servos I would be more than happy to connect them to a 2S lipo, the letters HV after the number indicates that it it would be quite safe to do so; and to be quite honest, it’s the only way you are going to be able to supply them with 7.4 volts anyway. Other than using other higher voltage multi-cell batteries, of course. If Corona were slightly more pedantic they would have indicated the voltage range as 6 to 8.4 volts. All these electrical items have a nominal, or name plate, value. Take for instance the common or garden car headlamp bulb. The nominal value of a car battery is 12 volts, so the bulb will be a 12V 55W (say). But because the bulb is mostly on when the engine is running the bulb’s input voltage will be around 14.4. because the battery voltage will be 14.4 volts. So there always has to be a bit of leeway built in, but the driver doesn’t worry or care about this. The nominal voltage of a 2S pack is 7.4 volts and there is a valid reason for this. I’d be slightly concerned about the receiver, though, I’d check this first, but I’m sure most if not all 2.4 receivers are HV. The Frsky ones that I’ve seen can be up to 16 volts. Also if I connected a 2S lipo to the rx I’d make sure that all the servo were HV, hanging a standard servo on as well would result in it quickly showing some displeasure; such as noticeably twitching and then possibly bursting into flames. It has happened. Good Luck… PB

Just to confirm that the DX6 transmitters I quoted that the schoolboys and myself used were indeed the original DX6is. Sorry if I caused any confusion. These always behaved impeccably, not so much as a single glitch in quite a lot of use; but there was an occasion when on one tx the aileron servos reversed of their own accord; I found the reason as to how this happened and was able to replicate it but why it should have happened I was never able to completely understand. There was a completely separate story at the patch at one time, too, about this odd aileron reversal on a DX6i. It can happen. PB PS If the later transmitters really are causing problems, and indeed resulting in models being difficult to control and crashing etc., then this would appear to be a remarkable step for Spectrum to take. Very unusual. Edited By Peter Beeney on 12/05/2016 11:12:21

John, I think that if you are trying to say this particular incident was down to pilot error I think I would have to reply that in this case this was very unlikely. There is no video evidence to corroborate anything one way or the other, but another flying mate that I’ve flown with on a regular twice a week basis for perhaps fifteen years who just happened to be watching remarked as it was going in “He hasn’t got that!”. When you’ve been flying for many years and spent a lot of that time on the end of a buddy lead you do tend to automatically register the differing situations occurring. Perhaps one alternative question I might ask myself is - “Why is it that only Spektrum pilots generally seem to suffer from pilot error?”. I’d certainly agree there are many incidents caused by pilot error, I’ve always thought perhaps in the region of up to 95% maybe, however, I do have some slightly historical evidence regarding Spektrum. In the very early 2.4 days 3 of us had Dx5e radios, 2 beginners and I had one to use as a buddy box because of the numbers of new learners with Spektrum radio coming along. The other two both had problems, one man lost two models, although in rather vague circumstances. But he changed to Futaba, which resulted in no more crashes, although that could of course just be coincidence. The other chap, now a regular mate, also had some incidents, one such was that when he was on a buddy with his instructor as they were on the landing approach with the instructor flying all contact was lost and the engine went to a fail-safe tickover. At the very last second the radio suddenly responded again, all was saved but they decided it was not wise to continue. So another Futaba sale. But this lad is nothing if not persistent, so he ‘flew’ it it safely tethered on the ground until the same thing occurred. With some careful tampering he established that squeezing the transmitter in his hands caused the RF output to fail but not to extinguish the leds on the front. When he examined the main switch he decided it really wasn’t up to the job so he simply by-passed it with a wire strap soldered across and to this day he uses it occasionally; he turns it off and on by removing and replacing one of the dry cells.The switch was faulty and I’m sure this has also been flagged by other forumites, too. The RF output has never been an issue; by the same token I spent some effort in trying to actually cause mine some grief but I was never successful. And as I mentioned previously, checking the brown out figures, I think on 3 separate occasions, led me to think my actual results were considerably different to what others were suggesting they might be. At least on my AR 500 receiver anyway. I think I’ve posted the exact information and details twice before… As someone remarked the other day, ‘Spektrum woes seem to be getting less frequent. But is that only because fewer people are using it?’. I don’t know, and I don’t have any axe to grind here, either. I gave my Dx5 to some schoolboys to use a buddy with their Dx6 transmitters. (Graupner is a directly straightforward buddy with Spektrum, so I’m ok). We never had any problems with 4 of these Dx6 transmitters, apart from my homemade leads acting up intermittently. When is a mono plug a proper mono plug? Only when it’s a Spektrum mono plug. The Spektrum plug is different (larger) in size, but only by half a minuscule; but that's enough for the standard plug to cause the occasional open circuit. So even the genuine Spektrum lead doesn’t appear to have any leeway as far as a reliable connection is concerned, but having said that I’ve never know this to be anything other than 100% reliable. So far…… Anyway, whatever would we talk about if radio gear became ultra reliable… PB

I’ve been doing homemade experiments with model radios right back from the days of single channel and 27 MHz, and I think that without exception there has always been a more than adequate ground range, that is unless there is specific problem with the radio that’s reducing the range; and I’ve always accepted that the air range can be up to 10 times the ground range, too. I’ve related this here before as well, but one little bit of tomfoolery we do is to place a 2.4 receiver on the seat of a metal folding chair together with a connected battery for power and a couple of servos. We then take the associated tx 660 metres (720 yards) to a point across a shallow valley that’s very close to a copse but it’s still a straight line of (distant) sight. A couple of mobiles as a comms. link, one each close up to the tx and rx. To make it interesting the rx aerial(s) always point directly end on toward the tx. Then to try and raise the sweat factor a couple of degrees even further we place 3 transmitters directly underneath the the chair. The strip is in-between too, and invariably someone is flying. I normally operate the tx, holding this at standard waist height, but pointing the aerial in every conceivable direction whilst operating the controls including directly toward and the opposite back to front, tx pointing away from the rx. It also includes a 5 minutes idle wait to check for any extraneous servo twitching from our close up transmitters. So far this has been always 100% successful, we’ve never seen a servo arm out of place when it shouldn’t be, so to speak. We started doing this when a friend installed an Assan 2.4 hack module in his FF9; and the Assan lightweight 6 channel rx has an aerial three quarters of an inch long, which looks to be just a piece of ordinary wire, sticking straight off the PCB. This seemed to set the de facto standard, if this kit was this good, what was the proper stuff like? This was a few years back, and it includes a Spektrum Dx5e and AR500 receiver, again faultless. As an aside I’ve also had several ‘brown out’ type dabbles with this receiver, I’ve previously published the results on the forum; plus including a number of ‘this is definitely not the way to do it’ type installations, breaking every rule in the book - never the suspicion of a failure!! This shouldn’t be seen as any form or example of a definitive test, check or example, there is no firm documented evidence. It serves our purpose, however, and in fact we haven’t done one of these for a while. Probably because we’ve not had any range issues recently. Still getting some Spektrum ‘deviations’ though, an experienced pilot having a sudden and unexplained total matchwood making episode just off the end of the runway only just the other day. But I’d personally now take a great deal of convincing that aerial orientation of any sort had any thing to do with it. Many many years ago I still can remember a class tutor, when I was getting in a tangle with some aerial theory calculations, saying that he wasn’t absolutely certain either and he thought it was all a bit of a black art anyway. Just simply another view for the thread really, but providing you have the space it would be an easy exercise to replicate, no special equipment needed at all. PB

Robert, Your claim to be new to electric flight would appear to me to be something of an understatement, in fact I’d be extremely tempted to say that you’d be very close to being in the expert class. Particularly as you both designed and built the Stirling after just one model previously. They both look to be magnificent models, I’d reckon that must rate a very well done indeed! I was just mulling over an answer for Martin, but you seem to have very succinctly done it for me. I think I had been intending to basically agree with him, but you would rather appeared to have reinforced the idea that additional capacitance is not always strictly necessary. And by some margin, too, I’d say. I’d consider that 900mm is not really a trivial amount for an extension, by any standard, and if all these models have flown consistently ok with these long power feeds then this must mean something… Love the 900mm lead length and 72 inch span remark by the way. Just my language. These figures I can totally understand. Quoting a 2000mm span, say, will always leave me cold. But then I did grow up using proper money… Maybe to some extent part of the reason lies in the fact that the esc is in the nacelle, I suspect there is a good draught of cooling air though there. If you can keep electrical items cool enough you can probably safely overload them by a considerable amount. I’ve just had a glance at 30A esc, this is in a foamie and it fits in custom made slot cut in the foam, quite tight fitting, but with an air duct straight to the front. It’s labeled 3-4 cell lipo. A pair of 220uF smoothing capacitors, marked 25V and 105 degrees C, (that’s max temp, I assume). 25 volts gives a bit of headroom for spikes and 105 degrees of temperature allows it to raise a bit of a sweat in safety. Because it’s a bit cramped in the battery compartment I did cut the power leads down to short, which can only help. Quite by chance when I was tinkering with it one one occasion I found the maximum demand took it over the 30A level by about 5 amps, and nigh on 40 on a fully charged pack; I use 4S, but as it has never shown any outward signs of distress I leave well alone. The model performs quite nicely, loops as big as you like and a turn of speed in a power dive. All good luck with your Catalina, would I be right in thinking you are going to use a couple of fairly hefty motors? Also I reckon you will stick to your previous proven route as regards the electrics; it obviously works well! If I were doing one of my own I would tend to err on the generous side with the cable size, to keep the resistance as low as possible, and the escs as well, it seems to me that if an esc is spec’d for 30 amps it will cope much better with only 20 amps. But that’s just me, and maybe I’m just being overly cautious anyway. Just reflecting back on the ESC manufacturers advice to add extra capacitance for a moment, this can only make good sense really. They can only provide for an average or normal length of lead, and they have no control at all what is connected to to their product so they cover all eventualities with this recommendation. And if you have a bit of experience with a soldering iron and like to have a little dabble with the sparky bits it’s a pretty simple matter to add these anyway; and even if it never does any good, it’s never going to do any harm! All the very best… PB Edited By Peter Beeney on 08/05/2016 22:57:03

I’ve always had a small problem with some of the general perceived ideas and procedures concerned with aeromodelling, and now maybe this is another. I’ve never really given this much thought, but I’m now beginning to ask myself is it possible that there is actually a real problem here anyway? I’d easily be convinced that increasing the lead length will increase the impedance, but for the amount of added length in general that modellers are doing will it make that much difference? I have noticed that sometimes the advice not to extend the battery leads is almost at the point of death, indeed very serious stuff, but is this because there is proof positive, or is it just because somebody’s mate at the patch overhead a rumour at his friend’s flying field… Certainly there is some indication that it ain’t always necessarily so, Kevin Wesley’s very nice looking Mossie is one such very topical example, although I’m sure he always operates it well within the limits set by the manufacturer, such as prop sizes and battery cell counts etc. I’m sure there are other instances that can be quoted, too. It’s perhaps not until you start to wander outside the parameters, (like me), that it might make a difference. And in which case, I can’t really then complain when it all goes belly up… Just to illustrate what I’m trying to say in all of this, another old favourite chestnut of mine is the two, (or more), BECs connected together with both of the infamous red wires still in place. In my opinion, I’ve aways thought that it doesn’t matter at all if they’re separated or not; the system will still work perfectly ok either way. Although I would consider that for a couple of reasons two in parallel together would be slightly more secure than one. Just a few idle thoughts, but if I have the occasion to ever want to extend the battery leads by a considerable amount I’ll certainly keep a close eye on it for a while, but I think I’d be unlikely to make any other alterations, at least in the first instance. PB

As I see it, the fact that because the power input into the ESC is actually rapidly pulsing DC this is going to result in a reactance. Reactance is the resistance of a circuit caused by the action of an inductor or a capacitor; an inductor can be just a straight piece of wire, but it’s almost invariably in the form of a coil. These react to moving or changing voltages and currents. Impedance is simply the sum of adding the resistance and the reactance of a circuit together, so I guess this will now have to be classed as an impedance, but fortunately the units of measurement are still ohms. When a current starts to travel along a wire it causes a magnetic field to surround the wire. During the time the voltage is building up this magnetic is also building up and is in fact also moving; and when a magnetic field is moving past a conductor, or a conductor is moving through a magnetic field, a voltage is created in that conductor. So our moving magnetic field is creating a voltage, or electromotive force, known as an e.m.f., which is in opposition to our applied voltage and is thus slightly slowing it down. This is known as a back e.m.f. When the current is flowing in a steady state there is no back e.m.f. developed, but when the current stops the magnetic field collapses, it’s now moving again and a voltage appears in the conductor, albeit if only for a short time. Our brushless motors can demand relatively large currents at times, and as Martin W said, the FETs can turn off very quickly, both of these situations will contribute to the strength of the voltage that’s then generated; a hefty magnetic field as a result of the high current flow and it’s fast moving too because of the quick switch off; this voltage can be now high enough to seriously affect other parts of the circuit. This is not at all desirable, so these ‘spikes’ are absorbed by the capacitor(s) on the power input to the ESC. Generally speaking, I would suppose that the manufacturer would need to make the ESC as small, light and as cheaply as possible. So to that end maybe he only provides just enough capacitance to cope with the inductance produced by the length of battery leads he provides. One of the benchmarks of a good capacitor is it’s lack of an E.S.R. (Equivalent Series Resistance); a perfect capacitor has none. Therefore I suspect a low e.s.r. is most likely going to be related to the cost, so as with everything else, it has to be a bit of a compromise. Is is possible that the cheaper the capacitor is, the greater the e.s.r. is, and that the hotter it gets, for the same set of circumstances? Ohm’s Law says that the resistance of a piece of wire is proportional to it’s length and inversely proportional to it’s cross sectional area. So if we double it’s length we double it’s resistance; if we double it’s sectional area we halve it’s resistance. Adding extra capacitance to the circuit as has been advised by others, including the manufacturer, seems to be a good workable answer if it’s essential to lengthen the battery leads by any significant amount. Once upon a time I had a hotliner powered by a sizeable 2.3 to 1 geared Aveox inrunner, with maybe up to 2 kilowatt output on a good day. Back in the day the Aveox was considered to be quality kit, the ESC was never a problem, but the large exposed capacitor on the power input got hot enough in normal use to turn dark brown and totally discoloured. I guess it got pretty hot at times; but it never gave up. The motor had a rotor position sensor and I occasionally had to repair this, the thin wires tended to break. Also I was asked to look at an ESC that was running erratically and I found that one leg of one of the pair of smoothing capacitors had come adrift. The repair instantly cured it. It would appear there is no doubt that these little caps really are essential items…….. As always, just a few random ramblings. PB

BEB, I think you’ve just simply summed up a large slice of human nature generally in a nutshell…. ….and then applied it to aeromodelling…. Fortunately though, as you say, for some of us it’s not entirely lost, there are still many instances and examples of folks with the very opposite views and outlooks… PB

Keith, If you are checking the continuity simply between the 3 wires into the motor it very much sounds as if there is some sort of internal break. It’s most likely wound in star, so it may well be where all three ends are terminated together. If so, then the replacement is really the only solution. Star or delta configuration, there will always be permanent continuity between all three wires. Good Luck. PB

Generally speaking I don’t have many problems hooking up cells together, either in series or parallel, or at any state of individual charge, but I might be a little itty bitty cagey about using just the balance leads as the only connecting link. It’s certainly true that there will be little or no current passing down the intermediate wires but it might be that the first outside positive and the last outside negative will carry all the current resulting from the voltage discrepancy between the two packs, which in theory could be up to 1.2 volts/cell. Unless the packs are really adrift, when it may be even higher. When I tried whacking 1 flat and 1 charged 3S together at sometime in the past it yielded an instantaneous inrush 18 amps, although this was only momentary. And the balance leads are definitely not power wire sizes…… But I’ll agree about connecting them together as I’ve always liked the idea of parallel charging anyway. I have some 4 way parallel boards that piggy back with each other in series nicely, so providing all the packs are vaguely in the same ball park I just daisy chain them all together, switch on the charger and let them get on with it. Packs of any capacity flavour; but they all have to be the same number of cells; and as I don’t ever watch any batteries charging it’s never really a chore. One thing I’ve done, and I’m sure with many others too, is to utilise the nickel charge regime to get started. If your charger is capable, select nimh auto charge, set to say a 200mA rate for a 2000mAh pack. In theory this would take 10 hours to complete, so I’m sure you could leave it for an hour or so. Hopefully this would raise the voltage enough for the lithium charge to take over and when this gets as far as it will parallel it with another pack. If after a couple of cycles of this it still won’t play the game properly then probably the only option is to banish it to the tip! I never throw any batteries away, my own or other people’s, unless I’ve established beyond doubt they are not recoverable… PB

We have managed to revive some packs that have been left flat for quite a long period, such as a colleague that lost his model in a treetop in the middle of a large wood for six months. We had to wait for the leaves to fall to find it. Zero volts on test, quite understandably, but it charged up ok and he continued to use it. I’ve sorted a number of packs, including brand new ones that occasionally can be very reluctant; but the older ones certainly don’t always oblige; probably more failures than not, as it happens; it’s just pot luck; but always worth trying, there’s nothing to lose. And I have to admit I do have a very old but still serviceable variable bench supply which makes it all very easy to do. I do appreciate that few modellers will have one of these. I’d tinker with that for a while, try a bit of a discharge and re-charge. Two or three cycles might improve it. Also, if you have to bin it is it such a good idea to put it in salty water first? I take all old cells and packs to our local Civic Amenities Site, where they have a couple of heavy duty plastic tubs for small cells. A modern battery recycling plant will be more than capable of handling anything that’s thrown at it. If lithium cells do contaminate liquids that salty water has to be poured away somewhere, probably a drain, and you may just be passing it on. See the past record of Nicads to see where this goes……. Just simply an observation, Chuck, not meant as any form of criticism or even advice really… It’s just the way I do it…. PB

Why not just simply clean the oil off with a piece of kitchen paper, make sure there is nothing between the electrodes, replace the plug and run the engine again? After all, it’s all brand new, what difference will any staining make? As Ken implied, it will soon change colour again. I’d personally not let an engine that’s running in tick over much anyway. I’d add a bit more oil to the fuel at the very beginning, just to make sure on the lube, run the engine at full throttle for a short period and then allow to cool right down before doing it again. Gradually extending the time until it will maintain full throttle for several minutes without showing any signs of discomfort. My theory is that if I didn’t do this, because the expansion and contraction rates of different parts of the engine are so different at different temperatures, when I first tried an extended run at full throttle it would most likely seize. Now I can start to fiddle with the slow running; if it’s required, that is, maybe only a case of carefully getting the throttle travel adjusted to the slowest running point anyway but still ultra reliable. As usual, perhaps this just another one of my rather unorthodox methods of doing things; please don’t consider it to be any form of advice or instruction. PB

So I guess that on the basis of charging batteries in moving cars etc, I must now be eligible for a fair number of Darwin Awards… …and still ongoing, too… In terms of the actual car insurance, though, I have a perfectly good policy, which as far as I’m aware anyway, will cover a fire. My real problem is that in the event of this actually happening and the fact that the car now must be getting a bit rickety in the differential, so to speak, the company would only pay me the declining commercial value, rather than what it’s actually worth to me. Although I suppose that one aspect to consider (slightly) in my favour is that as the vehicle faithfully obeys the law of constantly diminishing returns, the less likely the insurance company will be concerned as to what caused the fire in the first instance. Therefore maybe I don’t have too much to worry about anyway. PB

Donald, It is quite often the ESC at fault in these circumstances, but not always. Have a close look at the ESC and if any of the FETS have been cremated it’s usually obvious by some burnt covering . If not, try giving all the wiring a good shake up, (battery disconnected), a misconnection can also have this effect. It could also be an internal problem in the motor, a broken wire say, not always so easy to find. Substitution is usually the best and quickest route, but in your present holiday situation that’s perhaps not easy, or even possible, either. The fact that the BEC working is certainly optimistic; but if it is burnt FETS then that points to possible overloading. Unlikely, I’d have thought. Over time I’ve seen a number of dry joints on the wires and connectors, far too many, I’d say, and invariably a case of very poor soldering, so I’d certainly have a good tinker with this first, try giving the connectors a really really good pull to start with. If you are lucky and you get some response then it means you should have a good butchers round it all, at least at some point in the future. If you manage to get it going now, and you don’t fix it properly, sooner or later it will return to haunt you again! All the Best of Luck.. PB Edited By Peter Beeney on 12/04/2016 18:10:56 Edited By Peter Beeney on 12/04/2016 18:13:16

The SC 52 two stroke has been known to occasionally break the odd crankpin or three; could the four stroke be something of a copy cat? A a quick glimpse in the crankcase will reveal all. Unfortunately, I’m told that a new crankshaft may be fairly expensive, too. Good Luck PB