Andy Freeman Posted November 20, 2008 Share Posted November 20, 2008 Looking for a lightwieght solution for my long running multiplex Fox conversion.I have been told that a 2S liPo can be used without a voltage regulator. I doubt that but a nameless purveyor of flying boys toys is adamant it will be OK...Who is right....? Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 20, 2008 Share Posted November 20, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Andy Freeman Posted November 20, 2008 Author Share Posted November 20, 2008 I did tell them it was a cheap and nasty GWS Naro thing and 3 3.xg servos. I actualy rekon it might be better with 1S (but was concerned the reciver might not have enough juice. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted November 20, 2008 Share Posted November 20, 2008 1s LiPo will be too low, and 2s "neat" is not advisable IMO. THe simple answer is a 2s and cheap standalone regulator of which there many around ( the ones I use cost about a fiver, and even include a low voltage warning alarm that sounds if the battery drops to around 6V which is just the right time to re-charge anyway ). Alternatively, but probably no good for your particular case 'cos of the weight is 2 x LiFE cells ( A123s ) - these come out at 3.3V nominal..... and soon drop off to around 3V which is fine for most servos and receivers.They are heavier than Lipo although there are some lower capacity smaller lighter ones available too which should be OK for radio gear. These weigh only around half the "normal" M1s Quote Link to comment Share on other sites More sharing options...
Bradley Posted December 26, 2008 Share Posted December 26, 2008 I just got my Fox for christmas, thinking lipo single cell, it has just enough juice but not enough capacity.Where do you get those regulator's for a 2s Timbo? Quote Link to comment Share on other sites More sharing options...
nasa_steve Posted December 27, 2008 Share Posted December 27, 2008 any electric flight specialist or reasonable model shopnasa Quote Link to comment Share on other sites More sharing options...
Matt Jones Posted December 29, 2008 Share Posted December 29, 2008 I got mine Here. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted December 29, 2008 Share Posted December 29, 2008 Thas a very pricey unit for a .5A capable regulator !I got most of mine from Hobby City / KIng TBH. Personally I wouldnt use anything lower than 3A. How about this ? Quote Link to comment Share on other sites More sharing options...
Former Member Posted December 29, 2008 Share Posted December 29, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted December 29, 2008 Share Posted December 29, 2008 Or with 4 NiMH 210mAh cells soldered to form a 4.8volt battery. Will fly a fox around for hours and provide correct CofG.Available from www.component-shop.co.uk. Make up a couple and fly all day. Quote Link to comment Share on other sites More sharing options...
Andy Green Posted December 29, 2008 Share Posted December 29, 2008 Eric, my first thoughs were 7805 but didn't think anyone would know what I was on about, now there's a blast from the past.Andy Quote Link to comment Share on other sites More sharing options...
Chris Marshall Posted December 30, 2008 Share Posted December 30, 2008 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. Quote Link to comment Share on other sites More sharing options...
Phil_G Posted December 30, 2008 Share Posted December 30, 2008 Sorry to barge in but this thread has some slightly strange replies and I feel compelled to respond...First of all a 2S lipo fresh off the charger will hold 8.4 volts which, regardless of how quickly it might begin to drop, is far too high and will most likely do some damage. People confuse damage with failure - overvolting can easily cause damage but may not cause immediate failure. I'm surprised that the 'nameless purveyor' should give this advice.Re 'thinking lipo single cell, it has just enough juice but not enough capacity', a switching regulator will give you more capacity from a 2S pack but also adds to the expense, weight, and its another box to bury in the tiny Fox fus. A linear reg (ie 7805) wont give you any capacity increase from 2S. If the single cell voltage is ok but capacity is a problem, then surely the second cell would be put to better use in parallel with the first, or just make it easy and use a single cell of suitable capacity... many Fox users (inc me) are running a Corona synth rx and 3.6g servos off a single cell with complete reliability, although obviously not all sets are happy at this voltage.Re A123's, (we are still talking about an 80 gramme AUW glider aren't we?) their CV float is 3.65v so fresh off the charger a pair will read 7.3v which IMHO is also too high, yes they will drop to 6.6 which is better but still high and by then damage may have occurred. Again, 'damage' isnt always 'immediate failure', just because it works doesnt mean that no damage is being done.Amongst other things I teach BTEC electronics, and one of the course topics is 'reliability'. Running vdd within spec is a necessity for a reliable system.I hope this comes over as helpful I dont want to knock anyone or 'stir it up', although I do think the proprietors advice was at best 'suspect'. Maybe he meant to say 1S but said 2S.CheersPhil Quote Link to comment Share on other sites More sharing options...
Matt Jones Posted December 30, 2008 Share Posted December 30, 2008 Timbo wrote "Personally I wouldnt use anything lower than 3A."That's fine, and personal. I'm happy to use that for a 2 mini servo glider. Quote Link to comment Share on other sites More sharing options...
Bradley Posted December 30, 2008 Share Posted December 30, 2008 Phil,Where do you get a 1s of decent capacity then? I've been thinking 2 single cells in parallel, got the batteries from mini Helli's but I still don't think the capacity will be enough Quote Link to comment Share on other sites More sharing options...
Chris Marshall Posted December 30, 2008 Share Posted December 30, 2008 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. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted December 30, 2008 Share Posted December 30, 2008 Matt Jones wrote (see)Timbo wrote "Personally I wouldnt use anything lower than 3A."That's fine, and personal. I'm happy to use that for a 2 mini servo glider.This post is unclear Matt - but I presume you mean you are happy to use that one you linked to ?>If so, then I still stand by the suggestion that 500m/a capacity is too low for most applications - and the fact that you are using mini servos actually worsens the situation, as most minis take MORE current than regular sized servos not less. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted December 30, 2008 Share Posted December 30, 2008 A high capacity single cell is probably easiest to obtain by carefully stripping down a >2s pack. However this is outside the TOR for this thread, and not a job for the faint hearted / unskilled. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted December 30, 2008 Share Posted December 30, 2008 Chris Marshall wrote (see) 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. In trying to keep to the OPQ - the simplest way to achieve a "lightweight solution" is with a 2s LiPo and proper regulator ( preferably switching type not a wasteful linear "heat radiator" like the 7805 ). The other various posts about LiPo and A123s etc are all valid and pretty much correct. Although 2s A123 may well be OK unregulated on some servos, it is, as stated by Phil a tad high, and besides.... is certainly NOT a "lightweight solution". As also stated earlier...surely if that particular model normally requires a little noseweight, why not just stick to using LSD NiMh cells in 4s? Quote Link to comment Share on other sites More sharing options...
Phil_G Posted December 30, 2008 Share Posted December 30, 2008 Sorry chaps, as often happens, good intentions taken the wrong way, I humbly withdraw & revert to silent lurking.CheersPhil Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted December 30, 2008 Share Posted December 30, 2008 No offence taken here Phil, all you said was fine and true - stop lurking - you can get into trouble for that you know Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted December 30, 2008 Share Posted December 30, 2008 Slightly off topic but I can't help thinking that the Rx/Servo pack out of an E Flite Vapor or similar could be ideal for a Fox conversion and it runs off a 1s lipo.Can you buy those as spares I wonder. Quote Link to comment Share on other sites More sharing options...
Chris Marshall Posted December 30, 2008 Share Posted December 30, 2008 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! Quote Link to comment Share on other sites More sharing options...
Chris Marshall Posted December 30, 2008 Share Posted December 30, 2008 Psas I said (and Timbo) all you said was true. Quote Link to comment Share on other sites More sharing options...
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