Peter Beeney

Exactly so, Mike, but I’m still a little sceptical in parts. Multiplying the amps by the generated voltage to get the output power is surely just measuring the heat generated again, not the mechanical turning force? This may well be ok when the input and output power ratings are as close together as they are going to get, but not so accurate when they are far apart. Your 9V example in the last paragraph, as apposed to the previous 10V, would appear to show the way this is developing. You have the ability to do the calculations so you would be well aware of whats what but I might simply look at the 387 watts displayed on my watt meter and think what a nice powerful motor I’ve got; this is exactly the reason why I’m saying I would be a bit cautious when comparing figures. Also the sentence: ‘The motor is also measured to by running at 10,000 rpm,’ does that imply you’ve also clocked the rpm with a tachometer? If so, how often is this action quoted, recommended or even mentioned? I seem to have missed it. As it happens, a tacho is always right on the top tray of my toolbox together with a new CR 2025 cell, it’s bound to go flat just when I need it…I’ve found with a bit of practise this can give me a great deal of information. Frank, I think I would like to try out the bits and pieces listed in Mike Downs’s OP on the bench for myself. For instance, what (low) cell count pack would I be using to keep the amps at 50 or below on a 12 x 8 prop? Also what are the revs, this is where I start, it will give me a good indication how the model will fly amongst other things. Mike B mentioned his ‘good’ 12 volt battery, (able to sustain 12v under that sort of load!), I use a fully charged 12V car battery for bench testing motors, now that is a nice stable supply! If I had a model that required a larger slower propeller I’d want to obtain an appropriate motor that still allows me to use it at it’s optimum revolutions point. Nigel, I’m not sure a propeller is any sort of dynamometer at all, but with a bit of trial and error, or as in my case, poke and hope, it will give you a fairish visual indication of how well or not your model will perform. At the end of the day I probably don’t really need to know very much information at all, I can just tinker until I get it right. But a dynamo. will give me the point on the revolutions curve where it’s at it’s most powerful straightaway. Interestingly, I believe that model aero engines were once tested with a propeller. They needed to know the torque so that together with the rpm they could calculate the horsepower. In the first instance they bolted the engine on a torque beam which was variably weighted at one end and pivoted against the opposite torque of the propeller thrust; but there were some anomalies arising due to the prop wash etc. so they found the the dynamometer a better instrument to use. And somewhere in the distant memory banks I’m sure I’ve seen a picture of an early full size aero engine up to the same sort of caper… I simply said that I would be a bit cautious when directly comparing the output power of the battery with the output power of the motor; and also including i/c. That’s not to say you shouldn’t do it though, in fact I tend to subconsciously compare electric motors with i/c all the time, I suppose because I’ve used glow engines for so long I’ve a pretty good idea how they are going to perform. Again fine if the the electric set up is spot on but again if the watt meter gives an erroneously high reading it might be a tad misleading. However, I’m sure that as folks are using e.p. more and more the increasing knowledge and experience will lead to less confusion. I actually think the modern DC brushless motor is a real cracking lump of engineering. With it’s design features and some help from components like neodymium magnets and the very essential but equally as impressive Electronic Switching Commutator it’s a real little powerhouse; and I have noted at the patch that some are still running faultlessly after very much use, too, so in some cases at least their longevity would appear not to be questionable either. More power to your (electric) prop… PB

I think I would always be a bit cautious when it comes to directly comparing the output power of the battery with the output power of the motor; or indeed the output power of an i.c. engine, too. To my mind we are measuring two different types of movement here. I’ve probably got all this wrong again, I usually seem so to do, but as I see it the battery power measurement is electrical whilst the motor power measurement is a mechanical one. They are always going to equal each other in total, but the two different effects are not always what we really want. Generally speaking,* when a current passes through a conductor it has to overcome the resistance, an action which produces heat, and it at the same time it creates a magnetic field surrounding the conductor. Again, rightly or wrongly, I figure that the magnetic field comes for free; the cost, in our case here anyway, is that it always requires it’s accompanying current and that in turn is causing heat which we don’t want, at least in this case. The circular motion of our permanent magnet DC brushless motor relies solely on the reaction, or rather a deflecting action, of two magnetic fields, one established by the flow of current. The mechanical movement, or power, of the prop shaft is derived by multiplying the torque by the rpm and here we seem to be measuring the strength of the inter-action between the magnetic fields; to get an accurate measurement of the power we would need a dynamometer to read the torque and rpm to calculate the power; whereas placing a watt meter between the battery and ESC measures the amps and volts to give the watts. Unfortunately this is just measuring the heat generated, rather than the turning motion! To illustrate this let’s consider two points on the motor’s power curve. At the instant of start up the motor is stationary therefore the current flow will be at a maximum. If we were able to read our meters in slow motion the watt meter would read max amps, therefore max watts input (all heating effect) but although the dynamometer would read max torque there are no revolutions which equals zero power output; but of course this situation doesn’t last very long; the motor very quickly starts to turn, the current flow diminishes and the speed and current flow equalise at whatever values they ultimately reach. Right at the other end of the curve let’s consider the motor in a stalled state after running. Exactly the same situation, max watt meter reading into the ESC and motor windings but no power indicated by the dynamometer, again because there are no rpm’s. As before we are just seeing the heating effect, this time possibly indicated by the distress signals given by the power train in the form of an arising column of white smoke or worse. In my view these are the two extreme points and somewhere in between there is one point where the motor will run at it’s ‘best case’ compromise speed, where the two measurements are closest together. I suspect, in very general terms, this is most likely to be not too far away from the unloaded speed, but there are many different cases. For me this is an indicator of the importance of the resistance, or rather lack of it, of the total power train. Looking at a fictitious case of 3 circuits, with 3 different total resistances but the same 10 amps flowing in each, a) 1ohm, b) 0.1ohm and c) 0.01ohm; Then in circuit a) there would be 100 watts dissipated as heat, circuit b) 10W dissipated and circuit c) 1W. All hypothetical of course, to maintain 100 amps three different voltages would have to be applied, from a) 10V, b) 1V and down to c) 0.1V. But the magnetic field strength would be the same in each case so the mechanical power output would not change. I’d judge the quality a power train by the value of it’s (low) resistance and by the same token I’d always try and keep the rpm as high as possible, within the required performance envelope of course. * When some conductors are ‘super cooled’, that’s frozen down to near absolute zero, they tend to lose their resistance. In this state a vast amount of electricity could flow unimpeded, there is no heat generated by this but a very strong magnetic field could be created. This can be used to an advantage, indeed I believe I’ve read somewhere that the Large Hadron Collider at Cern uses super cooled electro magnets in the particle accelerator. I know nothing about it, though, does it also make it cheap(er)? to run, too? But I reckon one prevailing caveat at least must be the fountain-like eye watering cost of maintaining the low low low temperature… Just my idea on the subject and of course it does not take into consideration the other principles that enable the motor to function…and no assurances that any of this is correct, either… PB

Sam, Just a thought but usually solenoids have a mechanism to return the plunger to the off position when it’s not operated, very often a spring loaded arrangement. The version you are using would appear not to have this facility and because it’s a ‘pull in for on’ type I think it’s already in it’s operated state; and from the spec. it’s now held in this position by a permanent magnet which is cancelled by a reversed current pulse which reverses the magnetic circuit and just releases the plunger. Unfortunately, though, it doesn’t move the plunger to it’s extended open ‘off’ position, so perhaps if you lightly pull on the plunger whilst momentary giving it a short reversed current pulse you might find it will slide out. All a bit of guesswork and speculation here on my part but I’m sure you won’t do any harm by trying… if it works come back here and you might be able to use gangster’s M.O. with the servo; but with apologies to him, in a slightly different configuration. Good luck… PB

Yes indeed, Bruce, I do have to hold my hands again up to this one. Certainly had I picked up a lipo pack and taken just a glance it would have straighten out my thinking; …and I had one just a few metres away… In this case I’d merely transposed the cell one slot along the 2S balance plug, so the charger would have probably read the balance lead as a 2 cell pack with one cell missing and would not have started charging anyway. I put it down to an advanced OAP condition with a memory state that needs a spot of re-formatting… A very long time ago, back in a distant working life, I spent a great deal of time swanning around with a small bunch of other reprobates. I very quickly learnt that if you made the correct comment about a particular perplexing situation no one said anything very much at all; but if you got it a bit wrong the sky would instantly fall in… so it was a case of doing the proof reading first and making sure the homework was always up to speed. Unfortunately in this balance plug case I forgot about my own memo! But others have also made small mistakes, too, on one space mission to Mars I believe, one half of the team used the yard as a yardstick whilst the other half used the metre as a yardstick for their landing instructions! Later on one very confused capsule! And wasn’t the Hubble Space Telescope also launched with a bit of a fuzzy lens which later had to be rectified… There have been common positive connection systems in use, cars in a bygone age had 6 volt batteries with a positive earth/chassis connection. I can remember seeing those. Also some industrial systems using large storage batteries used a common/earth positive connection, the battery voltage thus always being considered negative with respect to earth. This meant some care had to be taken when connecting equipment designed for the standard industrial common neg connection, but with practise you do get use to sorting it out. Particularly so when using mains driven test or other ancillary kit, if not double insulated it would have a green/yellow safety earth which is commonly joined up with just about everything else. This could lead to some very odd looking conditions, we always got out of it by disconnecting the earth wire and anything else that prevented the circuits from being fully isolated from each other; something I guess would not fit very well, if at all, with today’s H&S lot, but this was a fair time ago. I think I really must try and get out a bit more to the patch for some model flying and spend less poking about at these computer keys; then that would leave me less scope for thinking errors and more time for proof reading. But it’s jolly nice to know that someone out there is always getting it right, all of the time… PB Edited By Peter Beeney on 05/02/2017 15:45:57

Yes indeed, humble apologies here to Dick, he’s absolutely right, of course. I didn’t verify this to start with and I’d assumed that the battery started from the positive end when in effect it starts from the negative end. I should have looked before I spoke, it would have only taken a moment, my memory is definitely now showing it’s age... Sorry again, I’ll just keep quiet on such matters… PB

Yes, I afraid I wasn’t absolutely clear on this, either. With the greatest respect to Dick, I would place the red pos balance wire from your 1 cell in the first positive end of your balance plug (whether 2, 3 or 4 cell is unimportant) and the black neg next to it. The black wire acts only as the neg for a one cell, but both neg and pos for a two cell; in this case it would usually be a different colour. You need to tell the charger it’s only a single cell; and any other connection position will simply tell it little porkies… But in the unlikely event that you do get wrong it will just say mute anyway. It has to be connected correctly to start up. Which of course does complicate the issue if you are trying to make the charger start if a battery only gets slightly out of it’s normal operating limits… PB

Jonathan, it very much seems to me that the charger won’t fire up until it sees a voltage on the balance port, but I’d suspect that any number from 1 to 4 will be ok. This is to absolutely ensure the charger has automatically set the right number of cells, because you are unable to do this manually. So what I would do is to make up a intermediate connector in the main lead with a ‘balance’ pair attached to the main neg and pos and then using a redundant 2s (three pin) balance lead but leaving off the black neg at the end. In fact such a lead would be ideal as the 2 wires into the connector to save a little bit of knitting. If you are a bit adept at tinkering with these little bits and pieces just bodge up a temporary lead to give it a quick whizz; and then when it works ok (I’m convinced!) you can make it a bit more permanent. Not much of a plan to try and kid the balance port that it has 2 fictitious cells connected, I’d say that it’s very highly unlikely to accept this anyway but if it did it might give your cell a bit of a headache, to say the very least… The balance port is the only way the charger knows what is connected to it… Good luck! PB

Belated post 1 edit. No such thing as a PPM/PCM receiver, it’s just one or the other; in this case PCM… I should proof read my own ramblings better! Sorry for any confusion… PB

Post 2 Regarding the aerial blanking and poor installation stories, I’ve again spent considerable time trying to actually create such a kettle of fish for real but I’ve never managed it yet; but I suppose I could now say I’ve just been unlucky in this respect. I’ve also related in a thread before the story of our stringent full range test (long!) including attempts at interference and aerial orientation. This again has been a total success every time, and that also includes a DX5e with it’s AR500 rx. So I just continue to fly on rewardless regardless… When I did a low voltage test on the AR500 receiver on two separate occasions I found it went down to 2.7 volts before it locked out; but at this point the servos were also seriously complaining of the cold too, so I arranged to keep them up to 5 volts and just reduced the receiver. Exactly the same result. Oddly enough, when I’d previously done a similar check on a 35 meg set, at the time I was interested in range distance combined with low voltage, I found the receiver still had range at 2.9 volts but ceased working completely at 2.8 volts; so in this case anyway a fail at 0.1V higher than the 2.4! We live and learn… PB

Post 1 I think I’ve always considered the term ‘failsafe’ in this context to be a bit of a misnomer anyway, any self respecting failsafe system will automatically go to a preset safe condition in the event of anything in the system failing; and how often can the user ‘adjust’ or perhaps better ‘tamper with’ the various ‘fail’ settings as a matter of course? Using a lift in a building as an example, I suspect that if the power fails when in use there is more than one condition applied which ensures that the lift car stops and remains at a standstill; and no one can interfere with this state, either. If the power fails on a model aircraft the control conditions will stay as they are, it will instantly be totally out out of control and if it just should happen to be a 10lb warbird with a 120 FS going at full chat and it impacts close enough to the pits such some debris finally finishes up there it certainly grabs everyone’s attention a bit smartish… I know this from experience…. All the way through my model flying times and tribulations I’ve never seen a case of genuine outside interference, but I’ve seen a fair few number of power failures, that situation may be (hopefully) improving now, but it still occasionally happens. A long while ago there was a very serious incident which led to quite a lot of comments and instructions, much of which related to failsafes, at the time this was the latest radio development. We didn’t fully understand much of this because some of it appeared to be contradictory or even impossible to implement anyway. So we decided to do our own experiments and try and decide exactly what the real live effects would be in the field. As it happens, I’d bought a fun fly model second hand with a Futaba PPM/PCM receiver all ready on board, and I also had a FF7 PPM/PCM tx, which I often used as a buddy. I spent time kicking this around until I was conversant with the PCM failsafe procedures and we then tried it with the model up in the air using a second tx on the same frequency. It was a bit windy that day, but with practise I eventually found I could tolerate the interfering signal for up to a few minutes at the time, from well up wind to well down wind although it was always going to finally come down, fortunately it was never ever going to get very far away. We even switched on a second tx at one point, also on the same channel, but that made not an iota of difference. However this little episode did inspire one of my long time friends and inspired modeller that was involved to drily remark “PCM radio sure don’t behave like wot it’s supposed to”. We never did pursue this any further, though, because it seemed a bit pointless. Every case of interference would be different. I did discover one interesting little snippet on the way though. In the beginning, whilst I was tinkering with this on the ground, sometimes the settings would function ok and occasionally they wouldn’t. At first I thought it was a fault but on really getting into the system I found it was a natural quirk of the FF7 tx/rx. The servo positions were set by holding the sticks in the required positions like as now, this memory was stored in the tx and the info. was sent to the rx as a short pulse, once on switch on and thereafter about every minute. When the combo was switched off and then switched back on again the rx had no settings until it received the first pulse. Usually this was ok, but if I switched the tx on first, (as normal) and then slightly delayed the rx turn on it was possible it had no settings for up to a minute… Which is exactly what my problem was… I considered that this might not be too much of a problem with ic models, from tx on to take off is invariably greater than a minute I would think; but an electric hot liner which is carried to the strip the battery connect up there and launch can be quite swift. So in theory I thought it was possible here to have a short period of flight with no failsafe settings. In those days the PCM radio sent the last good signal to the servo…and the ESC…so full throttle with no control… I never saw this flagged up or even mentioned anywhere so I don’t think this was ever common knowledge and I’m sure this was all very insignificant at the time anyway, but my personal point is - If there is ever a serious incident for which there appears to be no explanation, could it be down to some arcane and mysterious set of circumstances of which no one is aware, such as this one? And if this situation did happen I suspect it never would be investigated, either…

Tom, If I remember correctly the Fox plugs that I favoured way back were 1.5V, I still used the 2 volt cell though, I just adjusted the length of the lead until they were nice and hot! I think most of todays plugs most be about 2V, I’ve never had any problems with them, at least not as far as the power supply being too fierce. My cell in those days was exactly as onetenor says, a small 2V wet lead acid… I’ve done a fair bit of tinkering with plugs in the past anyway, such as checking power consumption etc. and in general they are quite hardy creatures, although they do tend to rather take the hump a bit when my colleague has plugged his glow lead into the 12 volt starter outlet on the power panel. I’ve suggested that he should change the connectors on the leads in order to polarise them but so far there’s been little progress. There might just be a tiny point here. When I attach my glow lead to a loose plug the only form of heat sinking the element has is the body of the plug; and if this is left connected and lit up for a fair period of time it can all get finger blistering hot. But when it’s screwed into the cylinder head that must act like an efficient heat sink, at least under cold starting conditions. So I’m wondering if this might make any difference to the brightness of the glow. When the supply cell is in good nick I suspect most likely not, but when the voltage is beginning to sag a bit and the element is only just about a weak glimmer anyway… The next time I’ve taken a cyl. head off for any reason I’ll do a bit of tinkering with this theory and see if I can establish exactly what, or if indeed anything, does occur. Certainly a soaking with raw cold wet fuel will dampen things down a bit, too, but fortunately electrical principles being what they are, the element’s resistance now goes down and the current flow therefore goes up and thus quickly brings the element back to all it’s illuminated glory… indeed, I’d now consider the same thing probably applies with the plug normally installed, the heat sinking effect just flattens the glow battery a bit quicker… As I remember too, the first new glow motor I owned was a Veco 19, circa 1959/60, this had a throttle coupled to an exhaust baffle which moved across the open exhaust port as the throttle arm moved. No silencers back then! This covered the port when the throttle was shut, I believe in an effort to try and make the slow running more reliable. This was for R/C use. This also had a 1.5V plug too, because I can remember having to buy one of the large 1.5 volt dry cells of the times; I think those batteries were also used for powering radio sets. PB

One trick that’s been tried many times when winding up a reluctant motor is to just place a finger momentarily over the silencer outlet to increase the tank pressure and force more fuel into the spray bar; however, this needs plenty of caution at the same time because it could result in the crankcase quickly becoming over flooded; generally it’s a very brief affair, say for only up to a second, at least initially; an overly flooded crankcase and a energetic starter motor might not really be the ideal combination with which to start the day… Having now said all that, this simple little strategy more often than not results in an instantly reassuring burbling exhaust… I like to see a nice bright glowing orange plug, I’ve always thought this does help with starting so I’ve always used a 2V lead acid cell as the power driver. For some time now my source has been an 8Ah Cyclon cell, this is very portable but it will maintain it’s 2V output for a long time and in dire conditions. Mine is often borrowed to help out when items such as power panels are suffering from voltage drop and other ailments, particularly in the winter. Which bring me to the next point, I always tend to try to impress on beginners the importance of keeping all their batteries fully charged, especially during the cold weather because this will soon expose the laggards; it’s very discouraging to spend a long time trying to start an engine and then finding the plug is rather dimmer than yesteryears proverbial Toc H lamp… …and I suspect that it helps to be of a certain advanced age to fully appreciate that remark, too… I’ve found that a short time spent giving the engine a little bit of help in the starting blocks usually pays dividends, then it mostly becomes a first or second flick jobby.. but there are exceptions, such as the Moki, (a few posts above). One or two modellers I’ve noticed seem to be quite content to just connect the glow and then continue to crank it on the starter until it eventually fires…or doesn’t… This is a bit too much like hard work for me… In a case like David’s I think I’d be tempted to concoct a little priming bottle with an extra dollop of castor oil added. This might at least help the piston seal when it’s cold and consequently the compression and the induction; and if it doesn’t do the trick there is no harm done, either. I’ve not used castor fuel for years but I always have a small bottle handy because I add a modicum to the first tank when running in; but even then that’s only really for a bit of insurance perhaps… PB

David, Once upon a time I flew a Chippahawk with a Moki 61 two stroke up front. This was a super engine, very much suited to the equally super Skyways model. The only problem with it was that through the autumn and winter months it simply just would not start under any circumstances. I tried every trick that I knew, including priming with a drop of Keil Kraft diesel fuel but always to no avail; the best it would ever do was an infrequent pop in the silencer. I soon concluded that there was little wrong with it because it normally ran so well; and having read the stories about the difficulties starting full size in the extreme cold and also previously watched my colleagues starting their diesel lorries early in the morning in the depths of winter during the late fifties and early sixties, they would get the gas blow torch going and warm the inlet manifold up I eventually had a rethink. Part of my work kit was a small Primus gas bottle/torch so as a very last ditch attempt I lit this up and warmed the very reluctant beast up. Lo and behold, one flick and it was away!! So this instantly became the order of the day and it was always a total success, I soon discovered that a few moments concentrating on the crankcase was sufficient, I could only surmise that it possibly helped any neat fuel to vaporise sufficiently to get that first firing stoke in. In those days I was a member of a popular busy club so you can imagine the ribald and fairly derogatory type of remarks that frequently accompanied this procedure; but I usually got my own back because it always started straight away… I even got proficient in doing ‘hot’ refuels, i.e. without stopping the engine; although I have to say this was probably just really just a bit of unnecessary bravado… Whether this was a one-off Moki or whether they are all the same I do not know… The model met it’s end in a midair with a small biplane on it’s maiden flight. His prop cut right though one wing near the root and it crashed heavily on a tarmac runway which broke just about everything. The runway was fairly big, but when you consider it as a percentage of all the surrounding acres and acres of grassland… Typically his model was undamaged which was at least one consolation and as with the other two midairs I’ve had there were only two of us on site at the time. Like many other modellers I’ve owned a number of Irvines over the years, from the first 0.40 with the Dykes ring, but from memory they’ve never been significantly difficult to start… Hope you manage to fix it without any more delay… PB

Peter, Just to jump in here for a moment, don’t worry, the parallel charge rate is always fully self controlling, it’s all to do with the voltage. In your example, charging all these packs at 7.2 amps, (that’s the 1 hour rate, or 1C), will allow the 2,3000 mAh packs to charge at 2.3 amps each and the 1.3 mAh at 1.3 amps each. This is because when packs are connected in a parallel configuration all the batteries must remain at the same voltage, it’s impossible for it to be otherwise. I just bung my exhausted packs of different capacities but all the same cell count on a multiple parallel board, set a fairly low charging rate and leave them on overnight in the back of the car; not to be recommended though, this is definitely not advice to do this I hasten to add, but I’ve personally never had any difficulty charging batteries and I personally don’t have any particular worries with lithium batteries either. If I did I wouldn’t use them anyway. I’ve done this for many many years now and it’s always worked well for me. Exactly the same situation applies during discharge too, if a 20A and a 1A battery were connected in parallel and then set to discharge the same voltage must appear across both right throughout the total time, whether that time be fast or slow. Or, of course, any number of packs in parallel… Hope this is of some help… PB

Daniel, Firstly many apologies for a lengthy and rather dusty chronicle here………. Regarding your thoughts on what to do regarding your power train for the Edge 540, with the greatest respect I think if it were me in the same circumstances I’d abandon this one for now and maybe replace it with a known and proven combination; something using a 3S battery might be nice and simple, I’m sure there are plenty of examples around. You’ll probably have time to do this as well, when you join your local club for some training it can take a while to really get going; and you’ll undoubtably see some models with similar power requirements that work properly… I’m sure you’ll find most folk are very willing to help… I do have to admit that this one is a little confusing. The designer seems have taken a specific quad motor and married it to a Castle Creations heli ESC; and although you’ve changed this for yet another dedicated heli type I’m sure these will operate together ok but it might unduly complicate matters. The motor is interesting, I’ve only checked the HobbyKing site but even here it has some slightly conflicting info. The general overview gives the power as 1000W @ 18.5V, (5S) and 800W @ 14.8V (4S); however, the specification panel tells a slightly different story, it gives the power as 555 watts with the max current being 30A and the max voltage being 19V. Significantly the overview gives the cell count as only 4 - 5S Lipoly, not 6S, - the spec’s max 19 volt level also limits the count to 5S. So it would seem that a 6S battery is definitely in unknown territory here… I’ve said for many years that aeromodellers can sometimes be rather good at taking a piece of equipment and straightaway trying to make it do something it’s not designed to do… Let’s just use the overview quote above for guidance as an example, say. 1000W @ 18.5V, and 800W @ 14.8V; dividing the volts into the watts gives a a max current flow of 54A; that’s a little bit removed from the spec. max current of 30A, and also this 30A figure divided into the 555 watts of power here very neatly gives us 18.5V, the nominal voltage of a 5S Lipoly! 6S takes us over the top and connecting a fully charged pack at 25.2V, (as you may well have unknowingly done!), takes us up to 6.2 volts over limit. Not the best of ideas, perhaps, it’s advisable if you are getting into this sort of caper you really really need to know exactly what is going on. So it would seem on the face of it someone seems to have generated some rather conflicting info and you only followed the instructions?. I’d have thought this to be a very unusual line of thinking, particularly when there are many power trains around that are far more appropriate. Having said all the above though, maybe I’m still not totally convinced. I’ve always been a bit of a poke ’n’ hope sort of a bloke and I’ve often deliberately tried to get various items to malfunction but with very little success. Of course if you cross battery leads or some such the effect is entirely predicable, (and visible!) but I’m simply talking about standard setting up procedures etc. So it’s difficult to understand quite why your motor failed in the way that it did. Certainly I’d say to be most unlikely to be an error on your part, this stuff should be bullet proof. Did your motor attempt to move at all? Was it in fact free to turn? Did you hear any beeps? Once you have the motor connected and if it doesn’t start and run up to speed when you expect it to, it’s very important to disconnect it instantly because if the ESC has for whatever reason fired up maximum current will be flowing into the motor; and you may not realise this until it sends out extreme distress signals; as you’ve now already noted. Incidentally, the beeps are always from the motor, not the ESC as is sometimes thought. As I see it, the ESC sends a quick squirt of audio range AC to the motor coils, this acts in the permanent magnet field to vibrate the magnets and motor can to create the beeping sound. Maybe a bit like a very primitive speaker cone. I’d say that if the beeps are correct all is well with the windings in the very first instance, I’d have thought any shorts for instance would result in very weak or no beeps. The substitution method is a very quick and convenient way of isolating faults, but of course you do need some spares kicking around. But this does come over time. I think that’s more than enough for now, all good luck with your adventures at the model club… PB

Touché, Ron, but I really wouldn’t want to be winding you up, either… PB

Elastic? PB

Thank you for your very kind thoughts and considerations, Ray, but perusing this from my usual sort of upside down/sideways angle I feel that my ‘permeance’ regarding my ‘conductance’ may well be of an adequate sufficiency… However, I do agree that my ‘susceptance’ is now certainly showing signs of flagging (as it often does nowadays!) but fortunately the hour is fast approaching when I’ll have some pleasure in taking a small ‘measure’ to ‘rectify’ that situation… I’ve now read the link at last and I’m rather of the same opinion as yourself regarding the amount of information; but by the same token I’d tend to think that some areas at least are worthy of some sensible discussion, if only to make a token point; but nevertheless motors will continue to turn props and models will continue to fly regardless… PB

So can we now now consider bringing ourselves right up to date here, just for fun lets change that car side lamp bulb for a modern LED type and then perhaps we may be able to shine a whole new non-linear very efficient white light on the dark, dusty and mysterious pronouncements of electrickity… No? Oh well, perhaps not then; I shall therefore just continue to motor on rewardless (or resistless, maybe?) in the gloom… Happy Landings in 2017. PB

Simon, Whilst I would agree that if this is an example to illustrate Ohm’s law it might be somewhat confusing; however, to be a bit pedantic I’d also consider that the resistance still has everything to do with the current that would flow when the motor is running. It doesn’t change in value; because of the way an electric motor functions it’s the voltage that actually changes; generally within a circuit if the resistance stays constant to vary the current it requires the voltage to vary. Also, in all honesty, in terms of electric motors for models (aeroplanes) at least, 30 ohms does seem rather a bit high, 0.3 ohms would be much nearer the mark. Or better still, 0.03 ohms… In fact, in power terms the lower the total resistance of the complete power train can be made the better - but undoubtably the monetary cost will also grow proportionally… I’ve not seen the link yet, so maybe I’m talking out of turn here, but it seems to me it does need something more of an explanation; using a motor to explain electrical principles might be a bit tricky! PB

Dave Hopkins @ 16/10/2016 12:10:02 Dave, I’ve just read this post and the comment I’d have to respectfully make is that just like Megawatt above all you’ve done is simply just changed the rules. You are now anchored to a fixed point, the 747 cannot do this because it’s free to go where it will. What ever the belt does, you will always be able to pull yourself forward. Although that’s within reason, of course, if the belt were clocking 200 mph rearwards the ride could get interesting; and don’t let go of the rope either, that might be a bit of a mistake, too! Still, at least you would see the way clearly by the glowing light emanating from the skate’s wheels. I’m always looking for the easy option, so why not clamp the skates to a folding chair, employ a winch as the far away anchor point, tie the rope to the cross bar and relax with a quick half and RCM&E as you are towed gently to the end of the belt. Stay cool! PB

Megawatt @16/10/2016 11:11:22 Megawatt, I do apologise for the late reply, I’ve been out flying… With respect, I’m afraid I’m still not yet convinced at all, so I guess we shall have to gently agree to disagree here. I’ve covered the plane on the belt so I won’t go there again, but there are a couple of the other small points to note if I may - The man on the treadmill. In my humble opinion the man reacts to the treadmill action, not as you suggest, the other way round. It’s support frame is bolted to the floor so that it can’t move about, but the man is free to go wherever he will. The belt can only ever move back or forth. In exactly the same way the 747 is free to go where it will on the conveyor belt. When the belt is moving backwards at 5.3 mph as the sole of his shoe bears down and touches it it is moved backwards at 5.3 mph. So now I would consider that his shoe, foot, leg and in fact the whole of his body is being moved backwards at 5.3 mph. He has now to generate a constant forward momentum with his leg movements, sufficient to exactly compensate for the backward movement. This is how he maintains equilibrium. And as I mentioned before, if you have any doubts at all about whether he is actually being moved backwards or not, check out the funniest treadmill vids clip. This demonstrates in no uncertain terms what is actually happening. Re. the car on the rolling road. Now we’ve changed the rules from the question a snifter. In the first straightforward condition the wheels will be turning at 30 mph. In the second likewise condition the wheels would be turning at 35 mph; the car is moving forward at 5 mph and in this situation if the rolling road has a finite length the car would eventually be winched off the forward end. If it were 5 miles long it would get there in 1 hour. In the third condition, simply increasing the road speed backwards by a further 5 mph will further increase the wheel speed to 40 mph. This because the car is anchored to the winch rope and cannot move backwards at that extra 5 mph; the winch will continue to haul it at the same 5 mph and the time taken would be as 1h as before. Whatever the backward speed of the road in mph the wheel’s forward speed will always be that value, plus 5. But the winch will always be able to reel it in at 5 mph. That’s in my view, anyway. Back in the thick fog of long distant memories I was a bit of a spanner man for a winching team for a while. Given a sufficiently powerful low geared winch and a shed load of block and tackle for extra leverage you definitely can generate some really serious pulling power. Enough to bend or break virtually anything as I remember. One big problem too, out there in the fields, could sometimes be is that of finding a suitable anchor point for the said block and tackle, because if you’re not very careful that’s the first thing to throw in the towel! Happy times! PB

I think I might argue with the same conviction that plane wouldn’t move forward, it would stand still. Relative to the observer and the surrounding air, that is. Belt moving backwards at 150 mph, that must now mean that the point of contact under the tyre is also moving backwards at 150 mph. The 150 mph worth of jet thrust is simply now holding the plane steady against that. The wheels are still turning at 150 mph. The belt is having to apply a similar worth of thrust backwards. Top kit, these Turnigy brushless motors! The post implies that the plane takes off normally regardless of any sort of movement underneath the wheels. That being so, then how is our stalwart runner on the treadmill able maintain equilibrium between himself and the backwards moving belt? Why doesn’t he simply keep running into the stand in front of himself? Eye of newt, and toe of frog, and all that… We should have a nice thick brew by Halloween… PB

Stuart Coyle @15/10/2016 20:52:50 Or maybe not, Stuart. The wheel is still only going at 1 mph. With respect may we consider this a little more closely? Let’s put an OP (Observation Post) opposite the wing tip and assume that these to and fro actions happen simultaneously; plus there is an adequate power input all round. When the wheel rolls forward the belt rolls back at the same time same speed and same distance. So the plane goes back to where it started from. But the OP can only see this as the plane standing stationary. When the plane is stationary it’s wheels are also stationary, for sure. However, the belt is moving back under the wheel at 1 mph, causing it to turn forward at that 1 mph. All the time they are in contact with the surface the wheels are only going to be able to turn at the relative speed between the plane and that surface. Think runner on the treadmill; his running motion is carrying his body forwards, at say 5.3 mph. But he has set the belt to run at 5.3 mph in the other direction. His adjustable speed moving leg action takes the place of the revolving wheel, allowing the seamless transition from motion to motionless and so a casual bystander will just note that his body is stationary above the moving track. He is having to constantly apply power to match that of the machine, though. But if any one doubts that the belt is not actually moving backwards at 5.3 mph it’s well worth worth watching the little vid - 25 funniest treadmill moments. But in the event this might be a bit hypothetical anyway. In our question I suspect something similar happens, but in very much smaller increments. Maybe it gets to the point where the jet is eventually running at full power trying to move the plane forward because the pilot has opened the throttles fully; meanwhile the rules of the question are always being faithfully obeyed and an equal amount of power is being applied to the belt but in the exact opposite sense; the result is just stalemate, neither can actually move. So a theory might be; If the power applied to the belt is greater than that of the jet it will be able to go faster and thus the plane will be carried backwards at the backward speed minus it’s forward speed as seen from the OP. That’s inevitable. But if the jet power is greater and therefore the plane speed is fastest it will likewise move forwards; it has no other option. In our special case though, the two powers are equal resulting in the fact that the plane has to remain stationary. Taken from the Sunday Morning Digest……… that’s my excuse… PB

Colin, Bob Burton’s little sentence says it all, really. Keeping to the rules of the original question, which is - The conveyor is designed to exactly match the speed of the wheels, moving in the opposite direction. So the statement - "The point is that the wheels can rotate at a rate faster or lower than the speed of the conveyor by either advancing or retreating on it." is rather totally nullified as far as I’m concerned, I’m afraid. If I accepted that then I’d have to accept any statement about anything. There is another little statement in another post - When the aircraft reaches 5mph the conveyor will be going in the opposite direction at 5 mph resulting in the wheels moving at 10mph relative to the belt so we have movement of the aircraft while the original statement is still true. This seems to be a common theme. Taking a closer look; ‘When the aircraft reaches 5mph the conveyor will be going in the opposite direction at 5 mph’ I have have difficulty with this for a start. The aircraft will have to have accelerated from zero through 1 - 2 - 3 - 4 up to 5 mph. What has the belt been doing meantime though? The question says that too has been accelerating at exactly the same speed and at the same time but in the opposite direction. Had this not been so, as in standard runway, then the plane would’ve accelerated normally but because it’s trying to move forward on a surface that’s moving backward at the same magnitude then the nett result must surely be that the plane’s still standing there and not going anywhere soon. The real clue must be that the wheels are in contact with the surface all the time and their rotation is strictly controlled by what the plane and the surface are doing; they cannot turn freely on their own. But I have to emphasise that this is only my view. Now this part - ‘resulting in the wheels moving at 10mph relative to the belt’. If I can go back for a moment to the microlight powered car at the oak tree, we left them moving at 50 mph in opposite directions. So are the wheels now turning at 100 mph? Not so, I’m afraid, it’s a mere 50 mph, the car is stationary relative to the tree and the road is moving underneath them at 50 mph. Thus they can only turn at this 50 mph. The saga continues… PB