Peter Beeney

One niggling little thought is that if the problem is in the model and the throttle stick failed to the shut motor down how did the throttle cut-off switch manage to do that? It certainly does seem a remarkable coincidence that it happened twice in succession, but I’m at a loss, for the moment anyway, trying to figure out how that might not be within the tx. I think that if the BEC cuts out for any reason the motor always stops instantly; the reason being that the BEC’s primary function is providing a 5 volt supply to the ICs that control the motor on the ESC. The motor won’t run if these ICs have no power. Hope you manage to find some sort of gremlin lurking about in there… PB

Post 2 And in the same vein I notice that a Danish company, (I think), has developed a supercooled generator for wind turbines at sea. The size is reduced but the output is greater. But it still has to rely on the wind blowing I guess. I can’t remember much info. although interestingly there was no mention of the running costs, I guess this soaks up some (a lot?) of that increased output. Although I’m sure it’s possible they’ve developed better conductors and better (cheaper?) ways of keeping it supercooled by now. I have read some snippets about renewables and it does seem that the maintenance and running costs are very expensive indeed. I too use a clip-on power meter for current flow checks, but in close collaboration with a rev counter. In fact I invariably reach for the tacho first; certainly to always check the unloaded kV first; from there I can often guesstimate near enough as to what is going on. Occasionally, in marginal cases, I’d use a contact thermometer to look for any possible hotspots. Drifting downwind and slightly off course now, but I’ve also noticed that the University of Stockholm have given NiMHs a bit of a dusting off - they’re now NiH2. In short they can make them live a very long life indeed. Very useful as massive renewable energy storage load-levelling/sharing lumps etc. Also automotive use perhaps, if they can ever get the various manufactures to agree to supply them in the first instance. A similar move to small lithiums would be nice… As it happens I have a nicad pack in a rechargeable torch, which is now about forty years old; …and still going strong! It’s a slightly daunting thought sometimes that this now stands a very good chance of actually seeing me off… PB

Post 1 May I just add another little ‘joule’ to the collection of gems here, as I invariably look at this in a slightly different way. First, making a simple statement to myself, - generally when a current flows through a conductor with a resistance* it creates heat; it also creates a magnetic field surrounding the conductor; the two conditions are independent of each other, the heat does not generally affect the magnetic field. Second simple statement to self, - power is defined by the rate at which energy is used, or energy divided by time. I always consider the mechanical output from the motor as being separate from the electrical input power inasmuch that the mechanical power, as measured by a dynamometer at the prop shaft, is the direct result of the interaction between two magnetic fields, it’s actually a deflecting action, whereas the electrical power, as measured by a watt meter at the battery is the result of the current flowing through the resistance of the conductor and simply creating heat. The magnetic field is incidental, it’s always there but it comes for free in this particular case. So because the heat produced is the main concern I’m now thinking that the value of the resistance is all important, it looks as though lowering the resistance will reduce the heat produced. Using the little formula again, I squared R, sorry about more arithmetic, if we consider a motor with a resistance of 0.100 ohms and a current flowing through of 10 amps then the the power expended as heat will be 10 x 10 x 0.1, which equals 10 watts of heat. If the resistance is lowered to 0.010 ohms the the result is 1 watt of heat and going down one more notch to 0.001 it will of course be only 0.1 watt. That’s just one hundred milliwatts. But as the amps are constant the magnetic field strength will not have changed, so the power expended by the motor shaft remains the same throughout. For me this resistance, or lack of it, is a bit of a Holy Grail as far as motors are concerned; and indeed, the resistance of whole power train needs to be as low as possible. With regard to the little power conundrum, if I stay within the motor’s parameters set by the manufacturer then I might just stay out of trouble. But that’s not always guaranteed either. However, if I start increasing the cell count then that might soon become noticeable, and I think this is what happens when I do. It’s an electrical principle that if we increase the voltage across a given resistance the current increases by the same amount and as a consequence the watts, (dissipated as heat), increase by a larger amount. 5 volts across a 1 ohm resistance = 5 amps, therefore 5V x 5A = 25 watts. Double the voltage to 10 then 10V x 10A = 100 watts, a x4 increase. But the magnetic field around the coils is created by the current flow only, not the voltage, so that can only increase by up to a maximum of 2 times, thus the torque can only increase up to 2 times, but the heat dissipated is now rising greater in proportion to the increase in mechanical power. I have to reduce the prop size to lighten the load to allow the motor to turn faster. If, however, I change to a larger prop, increasing the load, the motor proportionally reduces the rpm, the back emf reduces again in proportion, more current flows through the coils, and from the above statement the heat dissipation increases greater in relation to the decrease in back emf. It might soon start overheating. * If some conductors are supercooled they lose all their resistance, now I reckon an infinitely large current would flow, driven by an infinitely small voltage; but I guess the supply unit is always going to have some resistance, so that wouldn’t work, also there comes a saturation point where the magnetic field will not increase any further. But it has it’s advantages, I believe the coils for the electromagnets at the Large Hadron Collider at Cern are supercooled; I’ve mentioned this before in similar threads long ago. Did you see recently that they’ve mooted an even bigger one, 4 times the diameter and 10 times the power, as I recall. I’d think they might even have to have a specially lengthened cheque book to accommodate all the zeros to pay the monthly power bill.

supertigrefan, Yes, max torque when stalled because because max current is flowing, creating a max magnetic field around the stator coils. This is so because the motor is not turning, therefore there is no motional or back emf to oppose the applied voltage from the battery. Powered flight. The secret is in the word powered. Power is the prop shaft actually turning. In very general terms, the faster, the better; within the design of the motor, that is. The torque is required to maintain the turning motion with the addition of a load. In general terms, the stronger, the better. So for powered flight, torque is absolutely essential. When the load on on the motor increases the revs fall slightly. So the back emf also falls in an exact proportion. Therefore the motor’s net voltage increases by the same exact proportion, but as it’s coils resistance alway stay the same the current flow will to increase by the same exact proportion… The extra amps increase the magnetic field strength and thus the torque, holding the speed at this level; however, it can’t increase speed again though, because the back emf would then increase again, reducing the current flow again. It’s all a careful electrical and mechanical balancing act. Reducing the load returns everything back to square one. Perhaps not the most elegant explanation I guess, but I hope most of the basics are in there somewhere. Keep on sparkin’… PB Edited By Peter Beeney on 20/12/2018 15:40:39

supertigrefan, Dave Hess’s post above is brilliant, a careful study of this will give you a very good start. The motor is delivering max torque at zero rpm, what it’s not delivering is any actual useful power at all. We are looking at just mechanical power at the prop shaft, this is obtained by multiplying the rpm’s by the torque, power is the rate at which work is done and the rpm’s give the time element. In this situation the revs per minute equal zero, any number multiplied by zero equals zero, hence no power! And, indeed, for all the reasons in Dave’s post, this is not really a good place to be for very long, at any time… it tends to get a bit hot under the collar… …or should that be the rotor… A very brief of brief scribbles I’m afraid, but I hope there’s at least some sort of clue in there. Another clue regarding the heating element (sorry) of the story is the resistance , or lack of it, of the motor. All tied up with the current’s ‘Is it pushed, or was it shoved’ little debate. I’m sure it has to be pushed… PB

Royal Institution Christmas Lectures 2018. - Who am I? - Starts Boxing Day 20:00 hrs. BBC4. With Prof. Alice Roberts and Prof. Aoife McLysaght. Will be well worth watching/recording, I think. Re Old Warden and the old timers. I can remember the day Neil Williams was given special permission to try a circuit in the Bleriot because the conditions were so good. Unfortunately he didn’t quite make it, gently floated down in the adjacent corn field and had to be rescued! The broken propeller was on display for a few years after. Already have The Guns of Navarone and Where Eagles Dare in the can for yet another repeat… plus some others. PB

Coming at this from yet another direction, to my mind the ‘comparison’ factor must also play at least a small part in this. I’ve always thought that the battery cost might be related directly to fuel cost; something I’ve poggered over a few times in the last 10 years at least. So another fag packet calculation, (incidentally, empty ciggie packets are getting harder to find these days, I’ve not seen an empty Senior Service or du Maurier lying around for some time now) to decide between methanol and amperes. Leaving out all the hardware costs for a moment let’s look at a 5 lb 12 oz, 61 inch span, low wing sports model with a lump of Irvine 53 Mk II up front. This turns an 11 x 8 APC at 11K and for arguments sake soaks up 1kW in so doing. This runs flat out for 20 minutes on 9oz of fuel. (I have timed it, from 9oz start to an empty dead stick.) The model is quite lively too, with a theoretical speed of around 80mph. My fuel is straight synthetic with an extra pint of methanol added to each gallon to thin it a bit more. Let’s say it’s 20 quid a gallon. A gallon is 160 fluid ounces, so I’d get 160 / 9 = 17.8 full flights from a gallon. That’s a total run time of 20 x 17.8 = 356 minutes or around 6 hours. To get the same performance from electric I’d again need a kilowatt of power; actually I’d consider that’s a bit conservative, the i/c power measurement is at the prop shaft whereas the electrical power as measured by a watt meter is that which is flowing from the battery; and they are not quite the same thing; due to losses changing power from electrical to mechanical in good conditions I’d need to see probably 1,200 watts, 20% more, on the watt meter. In some circumstances the disparity between these two measurements can be very pronounced indeed. Anyway, let’s be generous and just call it a kW. In a random but practical way let’s select say a 5S 5,000mAh pack. To deliver a kW it would have to discharge at 1000 / 18.5 = 54A. Discharging at 54A would give me 5Ah / 54 = 0.0926 hours; or 0.0926 x 60 = 5.5 minutes flying. That’s a discharge rate of around 11C, nothing too drastic there. The cost of a 5S 5Ah pack is around £60. I get three gallons of fuel for that; this give me 18 hours of flying time. If I get 5.5 mins per flight electric, then to be able to fly for 18 hrs would take 18 x 60 / 5.5 = 196 charges and discharges. How would the battery be feeling after that? In my experience, a little bit jaded to say the very least. Also another point, the 9 oz of fuel gradually finds it’s way though the engine and disappears; the engine’s performance stays fairly consistent throughout. The model gets a bit lighter, thus perhaps improving it’s flight characteristics. The CoG also moves back a little bit, (I like back a little bit CoG; it helps to to give the elevator a tad more authority!) The battery weighs around 30 ounces, so the model now weighs 7 lb 10 oz, this stays constant and the motor’s performance can only ever (slightly) diminish throughout the flight. I fully appreciate this is all very speculative and perhaps my arithmetic is a bit wobbly anyway; and that there are very many successful electric models. Indeed, they’ve been winning World class competitions for quite a while now. It’s just that I’ve occasionally wondered what size of battery I’d need to get the same time flying time and performance from the model. Also I’m not sure why the Irvine is so economical; just the gently tickling of the needle valve perhaps; maybe an OS 55 AX would be twice as thirsty; very much the same spec. though, 1.25 kW at 17k. So I reckon a kilowatt at 11,000 rpm might just about fit again. Even if it did drink twice as much fuel the battery would still have to deliver the very think end of 100 flights to equal it’s duration. I have to admit there’s not much flat out flying for 20 minutes at the time for me these days. Even 5.5 minutes might require some written notification and preparation. And like many other folk I don’t count the cost very much anyway, I might find it slightly disconcerting to be constantly counting the coins. I can cope with single tasking, just… as for multi tasking, no chance… There is another option here too, I could go back to slope soaring, a little something I’ve fancied for a while now, as it happens. Now the motive power will be cheap enough, but the car fuel gauge might start to complain it’s a bit thirsty on a regular basis… It seems I can’t win… Please consider this as only another dusty and rambling chronicle, just my view… PB   Edited By Peter Beeney on 06/12/2018 13:02:00

I’ve also been doing this for a while now; in fact right from the time lipos first appeared on the scene. I just cut a small piece of hardwood to a convenient size, drilled two small holes through to match the balance plug hole centres, pushed two pins through, cut them to length, soldered on bits of wire as an extension connection point and bent them down on to the wood; well separated of course; and then covered the top with a good blob of epoxy. Also having had the big advantage of a variable bench supply I can clip the leads onto the wires and give each individual cell as much (or as little) stick as I wish. Plus also monitoring the voltage accurately at the same time with a quality volt meter is very useful. I have found that on the very odd occasion even new packs have one cell that needs a bit of a kick start, I’ve sorted a few out for fellow flyers over the years. Although in general perhaps the overall quality has latterly improved. Or people are buying from more reputable outlets, maybe… I’ve sometimes had a bit of a tinker with this stuff in the past, too. As I’ve related before, I’ve raised the voltage on a single cell in a pack to over 6 volts without anything particularly untoward happening. One effect it does have though is to increase the cell’s capacity proportionally on a subsequent discharge. However, what the cell’s longevity is after this sort treatment is I’ve no idea I’m afraid, I didn’t bother to try cycling much. Also discharging to zero and resurrecting, again with apparently little ill effect; at least in the short term. Usual terms and conditions apply. This is not a form of advice or instruction; for safety reasons this should not be tried at home; I also fully understand that should anything go wrong whilst I’m trying these experiments it’s entirely my own responsibility. PB

Going back to the OP for a moment, and with the greatest respect John, but may I ask just how fast is fast? I did a quick rough and ready fag packet calculation earlier and with the 4 inch pitch prop you quoted arrived at a theoretical speed of around 59 mph……which would seem to be at least adequate (to me) for that model if it’s the one in Stephen Jones photo. Digging a little deeper I then found some pretty comprehensive test figures for that motor. The example on test actually had a kV of 1850 rpm. There were many combinations of props and voltages quoted; but an APC E 6 x 4 at 10.8V = 57.7mph soaking up 118 watts . An APC 6 x 4 Sport, (i/c?) at 10.8V = 57.4mph munching on 124 watts. Unfortunately there wasn’t a 5.5 inch pitch listed but a Graupner Cam Speed 6 x 6 at 10.8 volts resulted in a theoretical forward speed of a very healthy 79.8 mph, burning 152 watts in the process; however that’s still only 14.1 amps, still below the max 16 amps current flow given for the motor. Hope this is of some interest… PB

Yes Stephen, I’d think the Cherry II would be ok, I suspect the 10 cell nicad LVC point would be about 10 volts perhaps, you might like to consider cutting the the 3S lipo power at a slightly higher point, do a bit of experimenting and then stay within the flight time limits. I’ve never been very fussed about LVC points anyway, I have a long time flying mate that generally flown small fast foamies for many years time now and he’s always gone right to the limit all the time without any particular problems. If you start doing some serious flying you may find those brushed motors soon start becoming a bit tired, at that point have a go at upgrading to brushless. You will like the improvement! PB

I’m not sure you have to worry too much, Stephen, I flew a Twinstar with the brushed motors on a 2S lipo for a long time without any problems at all. As it happens the gentleman in the linked article is actually talking about a 3S lipo, and the ESC cut-off is related to the battery TLC anyway, rather than the ESC, i.e. it cuts off the power supply at a predetermined level to protect the battery; perhaps it’s better title would be a voltage cut-off point; in your case about 6.5 volts if you can adjust it. In my case I just let it run until it began to sag a bit and then land. In my opinion the worst thing that can happen is the power might be cut off a bit early, resulting in a shortish flight time. I don’t think you will do any damage. If it fails to recognise the battery voltage at all the performance will eventually start to fail but at least that will give you an indication of the flight time. Good luck! PB

Just to add a few more snippets of info. about the Jungmann, it was actually designed as a primary two seat aerobatic trainer; and as it happened they did make rather a good job of it. Shortly after it went into service was somewhat overtaken, at least by sheer style and performance, by it’s slightly later stable mate, the Jungmeister, an expressly designed single seat fully aerobatic biplane of the nineteen thirties, again an extremely successful machine at doing what it was designed to to. However in many ways, whilst the Jungmeister was very flamboyant and showman like, good at controlled flick rolls etc.*, the Jungmann was perhaps better at precise aerobatics; in later life it’s wings were given a new profile for sustained inverted flight and it gained a 180 hp Lycoming engine; in this guise it was renamed Lerche, or Lark in English, and continued to participate in aerobatic competitions up until about 1970; the Jungmister had largely ceased to become competitive in the late nineteen fifties, I believe. *One of the superstar Jungmeister pilots was a Romanian, Prince Constantine Cantacuzino, he flew a 275 hp Lycoming version after the war and he would often perform his ‘sign off signature’ manoeuvre, simply approaching for a normal landing and when the wheels touched he would snap the throttle open, yank the plane back into the air and zip around a flick roll at about 20 feet, instantly stopping the roll when perfectly upright again and then landing on as though nothing had happened. Sometimes he would do this up to three times in a row along the runway. Neil Williams, the RAF pilot who became British Aerobatic Champion many times, owned a Jungmann, G-BECX, and even with it’s slightly less lively125 hp engine he gave some pretty awesome displays and would finish with the same little flick rolling party trick on landing. So I guess anyone contemplating having a go at replicating this with a model will need every last ounce of power they can squeeze out… I’ve often thought that nineteen twenties and thirties must have been one of the best periods in history to have visited air shows. The overall flying performance was going up all the time but the rules were still pretty lax. Geoffrey Tyson, a Chief Test Pilot for Short Bros and Saunders-Roe gave an account of his routine flying program when performing with Alan Cobham’s Flying Circus and as I remember a small part of it went something like this: ‘I would fly inverted up and down over the crowd at about 30 feet, (in a Tiger Moth?), where then the people looking up could clearly see my hands working on the stick and throttle…’ Those were the days! Good luck with that, too. PB Edited By Peter Beeney on 07/11/2018 19:00:07

With regard to the brass tubes in fuel tanks failing, it’s actually the methanol that’s the culprit; methanol can attack brass, sometimes quite quickly and vigorously too. I discovered this many years ago and I replaced all the brass pipe with small bore copper tube; there’s also been a thread or two since on the forum chewing over this problem. As it happens, I’ve always used straight fuel anyway so it wouldn’t have been a nitro presence. When I was investigating this at the time I did read somewhere that the folks that go drag racing with high powered cars using methanol as hurry up stuff replace all the brass parts in the fuel system with stainless steel versions. I’d say very deep pockets are needed for drag racing… When the OS .46 SX (the one after the FSX, as I remember) first appeared on the scene a friend bought one and it almost immediately failed; he sent it back and a new one soon materialised with unusually a letter stating the the new type of nickel plating lining the cylinder wall was faulty. I think this problem persisted for a while, indeed it might still occasionally be with us, I’ve seen at least two LA .46’s that have died very quickly because of this and yet another one didn’t. My take would also be on the bearings causing the piston damage. I’ve seen similar a few times, I once had an Irvine .36 which got a bit noisy; being lazy I put off immediately sorting it and then one day there was suddenly no compression at all! If you didn’t know you’d have said the plug had been removed! Typically of course this happened when I was trying to start it as I was going to have a little burn up with a Frantic funfly at a local fete!! Quite remarkably a piece of a broken ball bearing had managed to embed itself in the piston’s skirt and had consequently cut a matching groove in the cylinder wall; this was quite deep so how it ever got to that point anyway I’ll never know. The rest of the piston and cylinder were also a matching mess… Unfortunately at the time I never thought to take any photos. In those days I bought all the engines and bits from ‘The engine man from Devon’, John D. Haytree, and on speaking to him he said “It’s not your fault, these are being a bit of a problem all over.” It seemed as though Irvine had bought bought some bearings that were marginally not quite the right size to start with and were also not entirely the best quality either. Perhaps things were just starting to get tough modelling wise even back then? But he did remark too that it was amazing just how any bearings would last as long as they do in model engines… I never met John but I did speak with him and his good lady many times. However, a good flying mate always that went to Devon for his holidays would always call in to see him for a chat and a cup of tea. On one occasion John was running a new version of an OS engine and it transpired that OS would often send him their newly designed models for his evaluation; the performance specification would then generally be based on his results. All in all he was a very nice and extremely knowledgeable bloke… PB

cymaz, I’ve just been browsing though the very capable Mick Reeves site as linked by Don F and it throws up some interesting info. and comparisons. His own reduction unit is the Torquemaster and is attached to the Zenoah 62cc engine. It’s reduction scale is 1.75 : 1 and he finds the best prop is a 28 x 14 which turns at 4,400rpm. So this would then indicate that the crankshaft speed is 7,700rpm. Significantly he does remark that the 32 x 12 at only 2700rpm is too big for max power… He’s installed this assembly in his one third scale Sopwith Camel which has a span of 112 inches and weighs in at 30lbs or 13.6kg, so it would appear to be very light. However, he also says that it will fly straight and level on one quarter throttle and will perform scale aerobatics on half throttle. But he qualifies that by saying that’s it’s nice to have the extra performance in hand for use when you want it. He also mentions prop slip and the like which I didn’t take into account, and I didn’t quite understand his figures anyway; I’ve read other articles about prop slip etc. and they often offset this to some degree by taking into consideration the fact that the propeller will unload in the air and thus turn faster. I imagine that today’s all singing and dancing telemetry functioning radios can already now get quite an accurate handle on all these ‘in the air’ situations. Very useful for future reference perhaps. Incidentally, applying the same logic to Bert’s Zenoah, if the crankshaft speed is 8,000rpm then the forward speed will be about 49mph without any other correcting factors… Mick's 14 inch pitch prop gives the Camel a speed of 58mph flat out... PB

cymaz, Just thinking in very very general terms here and I may be way of the beam anyway; and I’m also assuming the 7,500/8,000rpm is on direct drive; so if you were to use a 2 : 1 reduction unit this might give you a prop shaft speed of around 4,000rpm. It seem to me that the SE5a’s one third scale air speed would be in the order of 46mph, but if you were using a 32 x 8 inch prop at 4k it would only give you an air speed of about 30mph, perhaps not quite fast enough really, in action I guess the pilots were at times trying to muster every last ounce of urge they could! So to reach an air speed of around 46mph you would need a minimum 12 inch pitch; or alternatively a 1.7 : 1 gearbox would give you 4,700rpm which results in around 44mph on a 10 inch pitch prop. All of this stuff is back of the fag packet of course, and I tend to think the reduction gear makes the revolutions more obtainable, but by the the same token the gearbox inertia might tend to soak up any benefits… Hope this might at least be some sort of starting point… Good luck! PB

Chris - I certainly wasn’t intending to be in any way critical of G-JIMG or George at 4MAX, I was simply interested in the definition of a mismatch between lithium polymer packs when connected in parallel; and I certainly didn’t intend to post anything that directly contradicted anything that George said; or even only slightly contradicted anything he said. Neither was I intending to post something that is directly the opposite of what George advises, indeed in my previous post about paralleling lipos I did say that that it was ‘not really a comment on how to parallel packs and cells, this is just a statement of what I recorded when I tried the worst case situation.’ Many apologies if this is how it appeared to be… If G-JIMG choses to connect and power his model with two separate packs I don’t have the slightest problem with that at all, there are many ways of skinning a cat, as they say. That is until the momentum starts to get a bit of a wobble on, though; then if you’ve not taken this possible situation into account things can get a bit tricky. I’ve noticed it does happen occasionally with model aeroplanes… I tend to base my actions on the experience of spending many years in a previous working life tinkering about with things electric, including occasionally connecting in series and parallel cells and batteries that clocked enough voltage and sufficient capacity to cause a minor lightning flash if you got it wrong! Fortunately I never did, I’m frightened of electricity, but I was involved in more than one investigation when it did happen. Hopefully this is not misinforming anybody… PB Edited By Peter Beeney on 18/10/2018 22:44:12

G-JIMG - With respect, but may I ask how you are considering, or describing, a mismatch, please? And indeed, how it might shorten a particular battery’s life? I’m only just asking out of interest… PB

With regard to the PPM/PWM conundrum I’ve always understood, rightly or wrongly, it’s really just a combination of both. Does the basic 27/35 MHz kit operate like this? The transmitter controls create a sequential Pulse Width signal which is sent to the Encoder which turns it into a series of very short pluses, each one being the start and end of each long pulse; so this now becomes a Pulse Position signal. This carries on to the transmission compartment where it Modulates, or is superimposed, on the carrier wave. Now it takes to the airways and has the title Pulse Position Modulation; it then reaches the receiver and after being Demodulated by the Radio Frequency section is send on to the Decoder. This sorts out the string of short pulses and turns them back into a sequential Pulse Width signal which in turn is divided up and sent to the appropriate servo. So I would say that strictly speaking the expression Pulse Position Modulation, PPM, is the more accurate description for this operation as it is this signal that is actually modulating the carrier wave. I think the word ‘modulation’ is often used just as as a general descriptive term, ‘Waveform’ might sometimes be more appropriate… This is a very very minimalistic account of affairs but it’s how I’ve always thought that this system works. PB Edited By Peter Beeney on 17/10/2018 11:03:42

Back in the day, when lipos first appeared on the scene and then balancing the cells when charging suddenly became necessary, a lot of discussion started up which suggested that before paralleling the packs together all the voltages must be exactly equal otherwise as stated the current transfer would be high and damage would occur. I wasn’t really convinced about this so in the usual pb ‘poke and hope’ tradition I tried a little experiment. Using two 3S 2200mAh packs, both in good order, I fully charged one to12.6 volts, and discharged the other until the open circuit voltage read 9 volts; it was definitely flat! I then just paralleled them directly together. I made a sacrificial item for the final connection; a short piece of heavy duty cable and a large croc clip. I didn’t particularly want to burn the sockets, I thought that perhaps this was the biggest danger. I used a clip on power meter to measure the amps and when I closed the croc clip on the wire the instantaneous current flow read 18 amps. This then began to tick down at about 1 amp per second until it reached a rate of about 8 amps. It then started slow further and when it fell to the 3 amp level I disconnected, nothing was going to change much from there. The two packs would eventually reach parity, cells in a simple parallel circuit will always eventually level out at the same voltage, whatever the circumstances; plus my power meter might not always be strictly accurate below 4 amps anyway. This would imply that the total circuit resistance would be around 200 milliohms, certainly the internal resistance of the fully discharged pack would be at a maximum. Nothing warmed up, at least to the touch. Both packs recharged ok and just carried on powering models as if nothing had happened. As it happened, I was not in the least bit surprised about any of these events. Not really a comment on how to parallel packs and cells, this is just a statement of what I recorded when I tried the worst case situation. If I tried it with say 6S packs the voltage differential would be twice as much but the internal resistance would also be higher so maybe there would not be much difference in the current flow rates. PB

Andrew Moore 7 @ 04/10/2018 17:30:56 Re range check; - take a quick ganders down this thread… PB

I think I might well be tempted to have at least one more look at the 3 motor connections on that ESC if it were me Dave. Sometimes the soldering on these things does leave a bit to be desired. I had a completely dry soldered connection on an ESC which lasted ok through the first owner and then for many flights for me until after a landing in the long grass the motor suddenly refused to run any more. When I eventually found the little gremlin I actually pulled the wire out of it’s socket cold. There is a photo here in my Hextronic Battery Monitor album, next to bottom row on the right. One simple experiment you might be able to try goes like this. With the heat shrink removed from the connections you should be able to latch a croc clip onto the sleeve and the wire where they join. Press it firmly together so that the teeth bite well into both at the same time; then each motor wire in turn. I reckon this at least will be good enough to prove if there is a dodgy connection or not. I know it’s not a given certainty, but I think that on the very rare occasion that I’ve seen any ESC power transistors blow they tend to resemble the leftover remains of last night’s burnt barbecue… You are right about the motor details being confusing too. So far I’ve not really looked that hard but there does seem to be a distinct lack of detail available. I’d have thought that a 480 brushless would be in the 20 -25 amp bracket so an 18A ESC might be a bit on the economical side… Having said that it does seem to be the supplied unit. As it happened I had a foamie that spent all it’s flying time with it’s supplied ESC overloaded too but it never ever blinked… But it did have it’s own bespoke wind tunnel cooling system which it slotted into as part of the design; and I think this was the reason it never became overheated… it definitely wasn’t through lack of trying… Good luck. PB

To try and answer the question regarding the duff cell in a pack that’s connected in parallel with another, both packs will discharge equally timewise but the total capacity will always be less than two good packs. If they are (say) 2Ah packs but one has a faulty cell reducing the capacity to 1.5Ah then the total will be 3.5Ah. This will happen seamlessly with or without any diodes. If a pack shorts out certainly a diode will stop any back feeding but I’m wondering how this might occur anyway. If there was a short within the pack I think the resistance might be low enough for enough current to flow briefly to perhaps cause a fire - which might then quickly become a bigger cause for concern. I’ve never read of any instances of a pack shorting out internally; if it were to happen I’m sure it would soon be reported. (Other than problems relating to counterfeit batteries that is; but then this situation could also equally apply to modellers as well, I suppose). Then there is the lipo hazard which is very familiar and well recognised but rather than go open circuit they simply self destruct and go on fire anyway. But as yet do many folks generally use lipos as a receiver power supply? In my view all this simply reiterates the importance of testing the individual pack’s capacity from time to time; at least annually perhaps; and just as importantly new items before they go into service. Cells fail gradually over time, and there is no outward indication of this. However, It’s possible to avoid this by about 99.9%, a simple onboard led receiver battery voltage indicator gives a constant readout of the battery state and I’m sure it would be very difficult to ignore a brightly glowing red lamp and take off regardless! Again, I’d put this very close to the top of any priority list. Please consider this as just my opinion… PB Edited By Peter Beeney on 23/09/2018 15:58:43

Bob, 2.8A sounds a trifle on the high side, maybe ok for a 25 volt input; so I guess the question maybe be with the motor’s kV figure. If your 9,000 rpm result on 6S is correct I don’t think it can be a 590 unit. However, as you’ve changed it for a similar unit it’s perhaps not that pressing now anyway. Still well worth having a little fiddle about around with to find out exactly what is going on. though, on the face of it this one does seem to like a touch of loud pedal too, one gentleman runs it regularly at 1750 watts static, that’s a 6S pack, 12 x 12 prop and a 75 amp whack of current. I’d estimate that at 22.5 volts and 75 amps the revs are in the 12,000 + bracket; that’s a theoretical forward speed of real hurry up stuff. Perhaps more than 130 mph! No wonder the owner says that when his Sundowner 50 goes by it turns heads. Almost overpowered then, even for an example of a Formula 1 racing lookalike model! Sounds like fun! PB Edited By Peter Beeney on 19/09/2018 22:48:40

Bob, I’m not sure those kV figures quite add up for starters. Assuming you used a fully charged 6 cell pack for the test then I’d expect to see around 14,800 rpm at no load. Even at 3.7 volts per cell it should still surely be about 13k. What was the current flow that you measured? I’ve checked a number of motors for their kV figure. Mostly they are about as per spec but they can be suspect. One I did recently was an completely unmarked can but the model’s write up said it was an 850. A test figure proved to be 600! The model appeared to be flying a bit slowly! But, of course, that doesn’t mean it will necessarily use excessive current. I use a 12V car battery for a nice stable voltage that I can easily read with a voltmeter and if the tacho is accurate, which it is according to the mains frequency, then I reckon you can get fairly close to what it actually is. I always check the unloaded kV first then the tacho / prop figures always gives me an instant indication of what is going on. I wouldn’t bet on anything but I think I’d be looking again at the kV figures in the first instance… The motor does appear to be a 1,650W jobby? Around 65 amps constant? Good luck… PB PS   Bob, reading the motor reviews you may not be that far off the iron anyway. Stuff like 12 x 12 props and 1700 plus watts I ask you...   Edited By Peter Beeney on 19/09/2018 19:00:37 Edited By Peter Beeney on 19/09/2018 19:02:21

T. W. S. I don’t think we have any figures or statistics as yet anyway, but what we do have is a general statement from the BMFA saying that there has been a significant increase in claims for members car crashing into other members vehicles or expensive aircraft in the pits area. Which I have taken to mean there has been a significant increase in insurance claims. (Plural). And then because we may not get the refund these claims have in fact been met. I’ve done r/c aeromodellling on a regular basis now for a number of years, I started to attempt radio flying in the sixties with McGregor and the homemade TerryTone receivers. Fortunately I just missed the valve operated gear and the 45 volt HT batteries! Overhaul I guess I’ve seen and heard about most situations but crashing into a car or an expensive model in the pits is one that’s so far escaped me. So my first thought was ‘ What are the Safety implications in this? Or subconsciously inverting that perhaps - What are the Danger implications in this? Then trying to get a better handle on it I thought that because the BMFA membership figures have remained stable for a number of years the routine procedures will have probably also remained relatively stable. Including the number of insurance claims. But I really can’t think that the standard of flying has deteriorated that significantly, particularly in view of all the training aids there are available today, so I agree entirely with BEB when he says “I don't understand where all these incidents are coming from?” Perhaps not prudent to comment further, but as I said before, I think my friend thought the car damage figures might have been slightly artificially high years ago. Not particularly squabblin’ hopefully, just sayin’ PB