Chris Marshall

I am considering a portable generator as a better investment than a stack of LiPos to acheive an afternoon's flying. It seems to me that I would be better off with just one or two packs per model and expect to lifetime them in a season, rather than a pile that I will not exhaust in a couple of years, after which time they will be deteriorating regardless of use. There is a vast selection available from several manufacturers, with a huge range of prices. Just as important there is a huge range of noise levels from barely audible to higher than the BMFA limit for model engines! The quietest seem to be significantly more expensive. I would be interested in anyone's practical experience with a generator, both in terms of reliability etc, but also in terms of the noise level of the model they have, and it's perceived acceptability by others. One of the clubs I fly at is electric only because of noise considerations, obviously there is little point in turning up with something as loud as an IC model! I don't need an explanation of decibels etc, I am just interested in anyone's practical experiences, obviously I don't want to spend more than I need to. Clearly some units are really only any use for a building site with relatively high noise levels, but I am hoping that I don't need the most expensive.

Engine Doctor, I'm with you on the original colour scheme. I started re-painting mine soon after I got it (3 flights) and it is still waiting to be finished, and no further flying. I used some of the special primer for this sort of foam on all the unpainted areas then masked and sprayed with Auto air colours, which are water based acrylic. I have had very good results on helicopter canopies and I'm not the only one apparently. The white primer coat gives a very good base on which to build colours. Al was going very well until I removed the masking whereupon some of the original paint came away! Seems that e-flight cut corners in their painting process. I am now waiting until I have renewed enthusiasm to finish the job. think I will have to use masking tape over all the original paint, peel it away and prime and re-paint any areas that come away. It may take a while as I found flying it a bit boring so there is no great incentive to finish it, and when I have I will probably sell it.

Thinking about it some more I think I would just continue to use the BEC in the ESC. I have a couple of Platinums myself which have a switched BEC and I think would happily power the two servos. The most likely failure is probably the motor which is being pushed to it's limit or beyond withthis setup. I have heard that the motors specified are quite variable in the magnet strength which translates into higher or lower top speed and hence power consumption. This is probably going to cause more variation that the little change caused by using the ESC BEC

Hitec (USA) support tell me that all their digital servos will happily run on two LiFe cells. I don't think yours are digital but they may still be happy if they are rated at 6V. 2 LiFe cells are 6.6V fully charged but drops very rapidly to 6V

As I see it the key thing is the internal resistance of the battery. I would guess at 10mohms for a 4S 35C pack which is the max allowed for e2k unless it's changed. The elevator servo may be peaking at 2A through the turns, assume worst case and say an average of 2A. Assuming a switching BEC this means a current drain from the battery of about 1A This will result in an additional voltage drop of 10mV. The motor is probably pulling about 40A flat out resulting in a terminal voltage of say 14 V The servo drain is therefore causing an additonal reduction in voltage and hence prop speed of less than 0.1% Because the power is proportional to prop speed cubed this means a reduction in power of just over 0.3%. You would have to be pretty good to notice that! A better reason for a separate battery is the possibility of failure of the main battery or the BEC, Because you do not have much weight to play with the choice of battery isimportant. It needs a high C rating- or to put it another way low internal resistance, so NiMH cells particularly small ones are a poor choice. two LiFe cells or if your servos will take the voltage LiPos would be my choice.

Single and dual conversion refer to the number of frequency translations that occur before the signal is extracted from the carrier. dual conversion receivers convert first to 10.7Mhz, then to 455kHz. The encoded signal is extracted from the 455kHz stage. with a single conversion receiver the conversion is straight to 455kHz. The incoming signal is in each case mixed with a local signal generated by the crystal oscillator. The crystal frequency needs to be different from the required receive frequency by the frequency that the signal is first converted to, hence the crystal is different for single and dual conversion sets. There are advantages and disadvantages to each. The number of filter stages will be at least the number of IF stages but may be, and normally is more. 

1. Swindon Model Centre2. Fast-Lad3. Hyperion Yak 54 40e 4. Horizon Hobbies

1 Mode 22 Oxfordshire3 Oxfordshire4 mostly self taught

Great thread, v. interesting. It has convinced me that I want a Chipmunk for next year, something I have been contemplating for a while. Just a comment on power and efficiency.  I thought that IC engines are normally quoted in terms of shaft power, i.e the power that goes into the prop, so the 2hp that has been mentioned is comparable with 1500 @85% = 1275 watts.  The efficiency of a bigger slower turning prop on the electric (and the reason for using gearboxes on early motors) will probably make up the difference. I am not disputing a low overall efficiency for IC engines, just that they are rated (I believe) in a different manner, due to the difficulty of measuring the energy input, other than as fuel consumption.

I don't think that the voting for 1 will be very meaningful as it is too dependend on geography. (There is no longer one near enough to me, and I have to get everything mail order)  If you had asked people to rate their nearest shop on a scale of one to ten you may have been able to derive something significant.   1 Best high street retailer - none 2 Best mail order supplier -Robotbirds and Fast-Lad joint. 3 Best UK distributor - Horizon 4 Best Kit - T-Rex 450 SE

Looks like a PUFFIN to me. 

My post (last night) also seems to have been lost. I also said no Warbirds, not even the Beaufighter ( Of which my father flew the last flight of the fullsize in Singapore)   I would like something elegant ,aerobatic and with retracts:   1. SF260   2.PC7   3. Super Chipmunk

Ps as I said (and Timbo) all you said was true.

Phil, hope it wasn't my comments!  I'm too thick skinned (just thick some people say) to take offence at anything as long as it's legal. You strike me as someone who has some idea what he is talking about. Not the sort of person who should keep quiet!

My original post was a comment on the unsuitability of 7805s in this application. My comment on A123's was not strictly relevant as they are much too heavy for this application, just echoing Timbo to sum extent and giving an example of running within spec, which the servos's and receiver I am using ( not necessarily any others) will be, even with the initial charged voltage of A123's. This would not be true for a 2S LiPo, with significantly higher voltage.  Apologies if my mentioning A123's caused any confusion.  Phil, it's a dangerous thing claiming any qualifications, look at the response to the recent Ohms law question! Having said that I would not disagree with anything you have said so far! For what it's worth I have a degree in Electronics and about thirty years as a practising designer.

7805 regulators have a specified dropout of 2.2V, so that as soon as the battery voltage drops below 7.2V the output will fall below 5V. Follow Timbo's link for one of the right answers.Also low drop out linear regs are available. I have been looking at this earlier today and have just ordered a 2 cell A123's pack. Ready to go complete with balance connector.  The servos I  intend to use it with are specced for 4x alkaline cells or 5x NiMH so I intend to run without a regulator (KISS principal) The receiver is a Spektrum so it will also be more than happy with the voltage.

I'm not the Messiah, I'm just a very naughty boy. I still want to win it though.

Yellow and purple ones on my arms!

Bert, presumably you now wear it on your arm! Pegs:  here's a completely unsubstantiated thought, the spring is a significant wavelength at 2.4GHz, could easily distort the polar diagram of the aerial, and the peg material particularly if it is damp wood could absorb some of the signal? Has the safety of modifying the aerial in this way been proven?

Eric, I originally thought that the relative proximity of the attenuated transmitter would be enough to overcome the signal loss and overide the signal from the remote Tx with Aerial extended. That is until, as I said earlier, exactly the scenario described arrived, and a one or two models were saved, because of the servo twitching. I.E. not theory but pracise.  If, on seing servo jitter you thought it was due to overloading, you would move the Tx away to see if it clears wouldn't you? If it gets worse it's a fair bet that your assumption was erroneous. I don't think it is guaranteed to work, as it depends on the relative attenuations, but it seems worth it to me, that is for those who are still on 35MHz.  These sorts of problems and  poor pegboard discipline are what decided me to sell all my 35MHz gear over a year ago. I haven't regretted it for a moment.  One club I know who operate a peg-on system allow two (or more) people to put their pegs on the same channel on the pegboard!  I agree with you that there is no compelling reason for pegs or pennants on 2.4GHz My interest in procedures for 35MHz now only extends to self interest in that I don't want someone else's out of control model in the back of my head!  Myron,- As far as the poor old 'output tranny' on modern sets I quote from the JR website: Once you've activated the low-throttle failsafe, do a range check. With your model on the ground, simply collapse the antenna on your 8103/9303, or remove the antenna on any of the 10 channel systems. With the engine running at mid throttle, walk away from the model until the engine goes to the pre-set position. Count your paces - you should be at 60 paces or greater. They ought to know, they are hardly likely to design a set that will suffer premature failure when owners follow their own advice!

I don't agree. If you get used to having a pennant on 2.4 and not extending the aerial you will not make the visual connection if you pick up a 27 or 35MHz set with a pennant. The fact that it is a different colour will not matter,as it is a different set, you will expect it to look different.There is more difference between pennant and no pennant than orange pennant and black penant. The bigger difference gives you the bigger clue as to what to do with the aerial. I do agree entirely (as I have already said) with the use of pegboards.  I personally do not intend to have anything more to do with 35MHz. In the event that I attempt to help someone with a 35MHz set ( or any other band) I would treat it as something new and think through it usage before ploughing ahead, that would mean all aspects- i.e rate switches etc, and aerial usage, as well as how I expect the model to behave. Notwithstanding, I am obeying the rules and I have a pennant on my 2.4G set, albeit one that is as visually unobtrusive as I can make it. Black is a good colour for starters!

The reason for the procedure is so that the transmitted signal is attenuated, so that if you are not on the channel you think you are, and there is someone already flying you will A) not shoot them down, and B) possibly tell from the behaviour of your kit that this is the case.  Not guaranteed by any means, but useful. A friend of mine has experienced this exact situation, and thus probably saved one if not two models. As far as the consequent mismatch of the TX output stage and increased heating, I think that it was probably quite a few years ago that this was any real concern. I suspect that nowadays if the handbook recommends extending the aerial first, it is only so that it is not forgotten.

That sounds like an argument not to have black pennants, i.e. if you have a pennant/channel flag you have an aerial that needs extending, if you do not you do not.  Real safety however lies in adopting a procedure and sticking to it, i.e. the point at which you exten the aerial should be the same each time you fly. This will depend on local club rules, my club require the aerial to be collapsed at switch on and stay that way until you have left the pits.

To clarify(I hope) I mean do not bend the aerial wires where they exit the case, just position the separate cases such that the aerial wires of one are at right angles to those of  another, and at any convenient location in the model, with more separation being better.

I believe that the aerials should be oriented in the natural direction that they exit the case.  Where these are in opposition the wires are two halves of one dipole aerial, for one receiver, e.g the satellite RXs, but where they are in different directions they are separate 1/4 wave aerials for two separate receivers within the same case.  Within those limitations arrange the aerials at right angles.