Chris King 3 Posted October 4, 2018 Share Posted October 4, 2018 Hi, I stopped flying electric planes probably 20 years ago and was motivated to get an unfinished (Astra) Spitfire foamie out of the loft after watching Battle of Britain Model Squad on the TV. Thought at least one flight would be better than it being forgotten for ever! I solved a couple of the problems that forced me to shelve it originally but I have a duff aileron servo which isnt made anymore. Can anyone recommend a replacement for Protech B109 mini/micro (?) servo please? Dims are 27x24x9 9g. Quote Link to comment Share on other sites More sharing options...
Former Member Posted October 5, 2018 Share Posted October 5, 2018 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Chris King 3 Posted October 5, 2018 Author Share Posted October 5, 2018 Hi Percy, Thanks for coming back. You're right a lot has changed! Choice seems the biggest change especially for servos. Its only servos (ill swap one of the other servos so the wing servos are the same and get two new for the rudder/elevator) and batteries I need so not too worried about price. Just want reliable ones so I dont have to cut any more access panels in the wing to get to the Y cable. Batteries are my next problem. The old NiCads arent holding much charge and I had them made by SR Batteries in the states as the battery shape was a bit different. Everyone seems to be going NiMh now but it's hard to find an equivalent pack due to different voltages and size of the pack. SR Batteries are still going so ive asked for a price but im sure that wont be cheap! Broken foamie hinge is the next issue with 50 different options for that! All good fun though. Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted October 5, 2018 Share Posted October 5, 2018 Try Overlander for batteries. I can't remember but they may even make you up a custom pack Certainly cheaper than going to the USA Edited By Peter Miller on 05/10/2018 08:45:52 Quote Link to comment Share on other sites More sharing options...
Nigel R Posted October 5, 2018 Share Posted October 5, 2018 Is that the main flight pack? You sure you want nicd/nimh? Everyone uses lipos these days. They're half (or less) the weight of nicads. Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted October 5, 2018 Share Posted October 5, 2018 Posted by Nigel R on 05/10/2018 08:56:43: Is that the main flight pack? You sure you want nicd/nimh? Everyone uses lipos these days. They're half (or less) the weight of nicads. ....which might cause CofG problems if the model was designed for Nicads. Also LiPo voltages don't often match up with NiCad voltages, and *might* cause issues with the ESC. I'm also guessing that if the model is that old, it won't be using a brushless motor. All these things are fixable - at a price! And I'm guessing that in, view of the age of the model, Chris will want to do this as economically as possible! I had a similar issue with a power assisted thermal soarer, designed to fly on 8-cell NiXXX packs. A 2-cell LiPo didn't have enough voltage, and a 3-cell too much. In the end, I fitted a 3-cell LiFe, which had almost exactly the same voltage as an 8-cell NiXXX, and mounted nicely on the CofG, avoiding any balance issues. Its still flying well today... -- Pete Quote Link to comment Share on other sites More sharing options...
Chris King 3 Posted October 5, 2018 Author Share Posted October 5, 2018 Im really looking for minimum hassle/cost to get some use out of an existing park flyer (Miss Moravia) and an unfinished Astra (foam) Spitfire which shared the same battery packs (neither brushless). It certainly is looking to be a custom pack. They are based on 8 x 4/5AA cells which were 1000mAh back in the day. I have a decent charger that can cope with Nicad/Nimh and dont really want to change that. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted October 5, 2018 Share Posted October 5, 2018 Yes, this might be the almost unique case that a NiMh pack may be best. Before you rush into getting someone to make a pack up for you, take a look around the model boat websites - it really is a charming trip down Memory Lane! Most of these guys are still in the sixties - well the start of the sixties anyway! But they very often still use NiMh packs and they have ready made packs in various capacities and voltgaes, brushed motors, ESC's the size of a bungalow! And if you think aeromodellers can be a bit "careful" with their money these chaps are in different league believe me! So prices tend to be good - electric motor for £4 for example! So, a look around places like Howes, Hobbies and Cornwall Boats etc might yield dividends! If you are unsure give them a ring - nice blokes. BEB PS No insult intended to out boat sailing colleagues - they are lovely chaps, just a bit "traditional" that's all! Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted October 5, 2018 Share Posted October 5, 2018 hello Chris, welcome back from me...things have moved on at a frantic pace in 20 years...maybe consider changing your power set up's to brushless/lipo' batts...…...you'll be current() and have a bit more duration and oomph....as for servos any of the adverts on the right hand side of the forum here will take you to suppliers...you may find stuff cheaper nower days and more reliable straight out of the box... main thing is enjoyo…. ken anderson...ne..1...… …..duration and oomph dept. Quote Link to comment Share on other sites More sharing options...
Chris King 3 Posted October 5, 2018 Author Share Posted October 5, 2018 Howes Hobbies turned up a 9.6V (which ive worked out is what I have) 8 cell nicad pack in same configuration but with full size AA not the 4/5s. Looking at both models I could just about get away with the extra size. Cheap as chips too at £9 odd. Would be very slightly heavier but if I look for the full AA size there seem to be many more options and I can see Nimh packs at 1500mAh for the same weight which would be an advantage - getting there! Thanks for all the advice guys - Think half the fun is sourcing stuff! Quote Link to comment Share on other sites More sharing options...
Chris King 3 Posted October 5, 2018 Author Share Posted October 5, 2018 Think I've cracked it. Component-Shop do a '9.6V 2600mAh AA NiMH Compact RC Battery Pack Vapex'. It will fit in both the models (just) and is lighter than the original (1000mAh) Nicads. Does the fact that it's 2600mAh mean it will last 2.6 times longer or will the motor go 2.6 times faster and explode? or is it not that simple. I get the whole LiPo and brushless thing. Brushless was just coming in when I gave up before. I have a conventially built model I bought from a club member years ago which needs a motor so may look into that in the future. Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted October 5, 2018 Share Posted October 5, 2018 Chris, the problem is that with NiMh packs the higher the capacity, the lower the current ability generally speaking. 2600mAh cells often struggle with supplying just servos and receiver, never mind the current needed by a brushed motor for motive power! I suspect a 9.6v pack will really be designed for use in a transmitter and will probably only have 2A wiring. As for the effect of the extra capacity, if the cells could supply enough current your motor would run at the same speed as with 1000mAh cells but for 2.6 times longer. Unfortunately because 2600mAh cells are really designed for lower current use the voltage will drop so your motor will run slower under load. You need to be checking the rated current output, which will probably be higher for the 1200 cells. Me, I'd stump up for a cheap LiPo charger and run a 3S 1800mAh LiPo which will be a slightly higher voltage at 11.1v than you NiMh pack but should be close enoughas your Ni pack will be around 12v after charging. That's just me though. Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted October 5, 2018 Share Posted October 5, 2018 In theory, the 2600 means it should last 2.6 times longer! BUT (and its a big one!), high capacity NiMhs tend to have a higher internal resistance than the old NiCads, which may mean that you can't draw as much current from them. If the price is low enough, it may be worth just taking a punt and see if it works or not. But don't be surprised if it appears down on power. (Of course, this will depend on how much power the model drew in the first place. If it was a modest amount, you may not notice the difference.) A 3S LiFe pack will be almost exactly the same voltage as an 8-cell NiXXX, AND deliver more current than a NiMh pack. 3-cell packs are not easy to find in small sizes, but I've spotted this one: **LINK** You will need a special charger for it, but any charger that will work with LiFes will also have a LiPo setting, and be useful if you decide to stick with the hobby. Money spent on good tools is never wasted, and chargers definitely fall in to this bracket! -- Pete Quote Link to comment Share on other sites More sharing options...
Chris King 3 Posted October 5, 2018 Author Share Posted October 5, 2018 Details said Max Discharge Current: 7,800mA Limit 3,000mA with Futaba/JST connector Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted October 5, 2018 Share Posted October 5, 2018 A little story to illustrate the point: A few years back, I replaced the ageing NiCads in the ignition system of my petrol powered helicopter with 2000mAH Eneloops (very similar to the Vapextech cells you are looking at). All of a sudden, I couldn't get enough power to take off! The engine started fine and ran smoothly enough, it just had no power! The ignition system used a capacitor discharge circuit. Although the average current was well within the cells capability, the *peak* current was being limited by the internal resistance of the cells. Hence the capacitor couldn't fully charge between firing strokes, and the power was reduced. Replacing the AA cells with sub-C cells provided an instant cure! As I said, depending on the current draw of your motor, you may get away with AA cells, but don't be surprised if there is a significant power loss. -- Pete Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted October 5, 2018 Share Posted October 5, 2018 This one? So let's call it 8A at 10v, 80W running the cells at their claimed limit. Not always realistic but let's be optimistic here. I don't know the airframe but if it weighs around 1 lb it should fly. Good luck Chris. Quote Link to comment Share on other sites More sharing options...
Chris King 3 Posted October 5, 2018 Author Share Posted October 5, 2018 Yes it was that one. Model is about 800g so well over 1lb (about 1.7lb) with the heavy old Nicads! So is the problem with the Nimh that its 2600mAh? Would going nearer the Nicads 1000mAh help or has it got nothing to do with the rating? Quote Link to comment Share on other sites More sharing options...
Nigel R Posted October 5, 2018 Share Posted October 5, 2018 Have to admit, I think the higher chance of success here lies with the recommendation of a 3S 1000mAh lipo & charger. The airframe will be 1/4lb lighter and fly better. The battery has more capacity to deliver current. Etc. If it needs ballast to balance, well, nothing lost. 3S lipo charger here, £10 https://hobbyking.com/en_us/turnigy-e3-compact-2s-3s-lipo-charger-100-240v-us-plug.html 3S 1000mAh lipo here, £5 https://hobbyking.com/en_us/turnigy-1000mah-3s-20c-lipo-pack.html Quote Link to comment Share on other sites More sharing options...
Chris King 3 Posted October 5, 2018 Author Share Posted October 5, 2018 Actually that does make for a good case for Lipo. I can buy 2 batteries and the charger for the same price as the 2 Nimh cells plus I get the bonus of a significant weight saving. Only downside is I cant charge in the field. Quote Link to comment Share on other sites More sharing options...
Former Member Posted October 5, 2018 Share Posted October 5, 2018 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Don Fry Posted October 5, 2018 Share Posted October 5, 2018 Buy a charger with 12 volt input voltage, most are anyway, charge off your car battery. Quote Link to comment Share on other sites More sharing options...
Ben B Posted October 5, 2018 Share Posted October 5, 2018 If you go down the lipo route get a cell checker / alarm also. Nicads/NIMHs you can deep discharge fairly low without impunity. Not true of lipos. A brushless ESC will likely have a Low voltage cut-off suited to lipos, probably not true if you're still using a brushed set-up / esc. Quote Link to comment Share on other sites More sharing options...
Chris King 3 Posted October 5, 2018 Author Share Posted October 5, 2018 When I was trial running both of them they cut the power to the motor early, I guess to keep power for the Rx and servos - not sure if thats the same? Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted October 5, 2018 Share Posted October 5, 2018 Another reason to consider LiFe cells over LiPos for this application - they tolerate a deep discharge better! BTW, if you decide to use the car battery to charge at the field, make sure its in tip-top condition! Don't ask how I know about this......... -- Pete Quote Link to comment Share on other sites More sharing options...
Former Member Posted October 5, 2018 Share Posted October 5, 2018 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
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