Jamie sawyer Posted July 25, 2014 Author Share Posted July 25, 2014 I've done a wee bit of research and I have a question regarding packs. Why do people as a standard fly on 4.8 volt packs any way. Why not 6 volt packs all the time ? I'm planning a few Fr Sky fasst Rx units and they take up to 10 volts max on the spec and most standard modern servos take 6 volts no problem..... Why fly 4.8 on board packs. I'm going to move to either 6V units or 2 cell lipos and fit a regulator in line. Lipos are lighter at the end of the day and just as cheap as NiCad cells. Maybe someone will shoot me out of the sky here and tell me why but It'll be a minimum of 2000mah from now on to with battery monitors on board also....once bitten twice shy as they say!!! Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted July 25, 2014 Share Posted July 25, 2014 Jamie As Paul Adams mentioned on page 1, Futaba radios have an Rx battery failsafe where, if the receiver detects the Rx battery voltage falling then it brings the throttle back to around 1/4 as a signal to the pilot to land sharpish. My money is definitely on this being the cause of the crash and not the throttle servo failing because you ignored the warning and carried on flying until the battery was exhausted. Your equipment tried to warn you! PS - don't think that a 6V pack will stop this from happening again. A flat or knackered battery is a flat or knackered battery. I would be interested to learn how you charged your battery and determined it was fit to fly. Did you cycle it? Did you use an intelligent charger that tells you how many milliamp hours it put into the pack or did you use the wall charger supplied with the radio? Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted July 25, 2014 Share Posted July 25, 2014 Posted by Jamie sawyer on 25/07/2014 08:52:31: I've done a wee bit of research and I have a question regarding packs. Why do people as a standard fly on 4.8 volt packs any way. Why not 6 volt packs all the time ? I'm planning a few Fr Sky fasst Rx units and they take up to 10 volts max on the spec and most standard modern servos take 6 volts no problem..... Why fly 4.8 on board packs. I'm going to move to either 6V units or 2 cell lipos and fit a regulator in line. Lipos are lighter at the end of the day and just as cheap as NiCad cells. Maybe someone will shoot me out of the sky here and tell me why but It'll be a minimum of 2000mah from now on to with battery monitors on board also....once bitten twice shy as they say!!! I believe it's historic - early reed and propo rc ran on an even number of cells, either 4* 1.5v dry cells or 4*1.2v Deac cells, because they needed a centre tap as they drove the servos in different directions by by using +3v or -3v from either end of the pack. Then came IC circuit based equipment, most ICs were only rated 5v before cmos came along. Because we traditionally use a nominal 4.8v servo power amplifiers and receivers continued to be rated at that figure. There are still a lot of servos around that are a bit edgy on 6v+. Most (but not all) will cope with a fully charged LiFe at around 7v which is similar to a fully charged 5 cell Nixx pack, but not LiPo at 8.4v Quote Link to comment Share on other sites More sharing options...
malcolm woodcock 1 Posted July 25, 2014 Share Posted July 25, 2014 It might have nothing to do with the crash but I think everybody should check linkages with this hot weather we are having, especially if model has been in a hot car. Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted July 25, 2014 Share Posted July 25, 2014 ps - under load a 1.5v dry cell will drop to a similar voltage as a 1.2v Nixx cell! Quote Link to comment Share on other sites More sharing options...
John Muir Posted July 25, 2014 Share Posted July 25, 2014 Bad luck, but that is probably one of the most comprehensive demolition jobs I've seen in years. Personally, I don't think anything about your gear was likely to have been a problem. My money would be on the wire-in-tube throttle linkage. If it kinked and jammed, or the throttle end of the linkage geometry wasn't quite right and the throttle arm stuck, then the throttle servo would be fully stalled and the current draw would go through the roof. After a while (not very long) the battery would get hot and run out of capacity. As the battery power dropped off your Futaba receiver would slow the servo responses and attempt to drop the throttle to idle as a warning that the battery is just about dead. Of course trying to move the throttle servo would only make matters worse and soon, with no power, the receiver would shut down. No response, no failsafe. no nothing. The plane then did its own thing, keeling over into a fatal dive with the engine unloading and seemingly increasing revs as it did so. I like these speculative threads: you can never be proved wrong. John. Quote Link to comment Share on other sites More sharing options...
Jamie sawyer Posted July 25, 2014 Author Share Posted July 25, 2014 Alan I flew the flight of 6 min roughly with the throttle at 0.......the stick was right back and also the trim!! If the fail safe kicked in due to power loss of Tx surely the throttle would come back all on its own to Idle and then I would have had to input throttle again. If the battery was fully depleated on take off then I would have lost all my servo control. This wasn't the case as I said in the post earlier......I flew for a further 6 Min in full control of the aircraft all BUT throttle!! I kept the aircraft in a safe manner well away from the pitts and down wind of the flying area. There was 2 reasons for the down wind flying 1.....was a better position for a dead stick which was inevatible due to the senarion. 2 .....Down wind kept it away from the pitts and also away from all public areas (Down wind was 2 miles of and long grass and lots of sea!! ) If the battery was the problem then it would have been a problem as soon as I took off. I wouldn't have just lost 1 servo Alan, it would have affected the whole on board electrics. Yes I do or did charge my packs from the cahrger that comes with the RC gear but this was a learning issue for me. I will now from now on use my modern digital lipo charger which does every type of battery out there. Its a Turnigy Accucell 6 which charges lipos from 1 to 6s, Nimh 1 to 15s and Lead acid 2 to 20v. I dislike your comment of " My money is definitely on this being the cause of the crash and not the throttle servo failing because you ignored the warning and carried on flying untill the battery was exhausted. Your equiptment tried to warn you! " You are very wrong! Its almost like you haven't read the whole thread and just stuck into me... And also you say a 6 volt pack wont stop this from happening in the future....now your just patronizing me. The crash was caused by a series of events happening. Loss of throttle first Cause: 1 : servo failure 2: Control link failure 3: Engine carb failure ( blockage in carb ) 4: Rx failure on ch 3 not likely is it but possible I have checked the control linkage as in the thread and it is intact including the link that was connected to the servo horn. All servo horn screws were installed also so the horn cant have popped off plus I cyanoed all allen key joints as I did the installation. I always do as an added security. I've inspected the carb and its functioning correct and smooth as it was before. Debri to be cleaned out of the port from the crash but you'd expect that. The only thing left is Rx or servo. I will probably never know because both are destroyed. Loss of power during flight.... This was obviously due to the battery loosing power. I had 6 min of flight before this happened. Obviously either the pack wasn't charged correctly and fully or it has gathered memory loss on the cells and the battery was past its best by far. Or the servo jammed causing serious power discharge to the battery during flight. I will check the battery thourally and it will most likely get recycled due to the severity of the crash. I have lost confidence in the battery now and even if it takes a good charge its not getting used now. I hope this clarifies it all for you . Thanks Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted July 25, 2014 Share Posted July 25, 2014 Jamie, one possibility has just occured to me - a loose cable flapping around and jamming the throttle servo in the open position. It's hard to avoid having either just a cable or a plug and socket (eg aileron extension) floating around and 99.99% of the time this isn't a problem. Maybe you were the 0.01%? Quote Link to comment Share on other sites More sharing options...
Jamie sawyer Posted July 25, 2014 Author Share Posted July 25, 2014 John I fully agree with you Jamie Quote Link to comment Share on other sites More sharing options...
Jamie sawyer Posted July 25, 2014 Author Share Posted July 25, 2014 Thanks Bob, we will never know fully what happend. Thats the really annoying thing!! Its all about prevention, learning and passing on the info to add knowledge of experiences at the end of the day. No one was hurt other than a patch of grass, a long walk to collect and a lot of match sticks. I'm in the process of checking and checking again my aircraft that I fly. Trying to illiminate this happening to me again. I've changed my battery pack to a brand new one I had lying around and checked my battery checker and installed it on a visible section on my fusalage of my plane that ill fly just now. Going flying again shortly so fingers crossed for a trouble free outing Jamie Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted July 25, 2014 Share Posted July 25, 2014 Jamie Futaba throttle failsafe is not the same as user settable failsafe. You as the user have no input over the positioning of the throttle servo when it kicks in. You can get throttle control back for a short time by throttling right back and then opening up again but it seems you might not have done that. I was only pointing out a feature of your equipment that you may not have been aware of and that may explain the way that your model lost control. If you want to reject my suggestions then feel free - it's only my opinion after all and it's very much a second had diagnosis. Quote Link to comment Share on other sites More sharing options...
Jamie sawyer Posted July 25, 2014 Author Share Posted July 25, 2014 Hi Alan , I have looked for the information on this secondary fail safe you have muntioned and specifically on Futaba website pulling up the RX which is a R617FS and I can't find anything. It is something I have to admit I was totally unaware of even existed. I don't dis beleave you but I'm struggling to find anything to read up on it. So if for example my transmitter lost signal to the on board RX the failsafe I mentioned would bring the Idle of the engine back to a pre set location which I had set to Idle and tested. Now theres a second fail safe where if the onboard battery is lacking power it will automatically inhibit the throttle control for a set period to inform the pilot on the ground that the onboard batteru was running low......hence you have to land basically and check your system..... I didn't know this existed, sorry... Is this a factory set failsafe built into the RX or can you adjust it at your transmitter. Some onfo would be appretiated...Thanks Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted July 25, 2014 Share Posted July 25, 2014 I think you need to read the manual for the Transmitter rather than the receiver. I use a Futaba FF9 and it has the feature. I'll dip into the manual and get the relevant bits. I know your transmitter is different to mine but I'm not sure why Futaba would drop this quite useful function. Maybe they have though... Quote Link to comment Share on other sites More sharing options...
Jamie sawyer Posted July 25, 2014 Author Share Posted July 25, 2014 I'll look my one out in the morning to, children sleeping Thanks for the quick response Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted July 25, 2014 Share Posted July 25, 2014 I've just looked at the manual for the 7C which is a later model than mine. Battery failsafe does still exist in the 2.4GHz systems. It's detailed on page 40 of the manual here: **LINK** Quote Link to comment Share on other sites More sharing options...
Jamie sawyer Posted July 27, 2014 Author Share Posted July 27, 2014 Ok here's an update on the battery side of things. I have since been cycling the battery in question . I'm not sure what was in the battery first as it had been on the trickle charger that comes with the Radio gear for maybe 8 hours but I now suspect the charger that comes with the radio gear isnt up to the task and it will be primerally for charging my Tx now. 1st cycle charger pulled 413 mah out of the pack put back in 580 mah. The charger then said it was full !!! Its an 1100 mah pack... So I cycled it again.... 2nd Cycle charger pulled 968 mah out of the pack...I find this odd but it is the numbers that the charger has presented to me after each cycle. Charger then put into the pack 1152 mah. I have since cycled it again but forgot to record the numbers Duhhh .... Do these seem normal for cycling a battery that has needed it ?? Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted July 27, 2014 Share Posted July 27, 2014 Yes it is normal. Your battery had reduced capacity. that's why it's not a great idea to rely on the wall trickle charger, especially if you haven't flown the model in a long time. It's best to cycle the battery a few times and if it's capacity comes back up close to the rated capacity on the label, then all well and good. If it doesn't then it's time for a new battery. I think it's clear now that your battery simply went flat in the air. Quote Link to comment Share on other sites More sharing options...
Jamie sawyer Posted July 27, 2014 Author Share Posted July 27, 2014 I'd say Alan......it definately did. I'm going to check my manual and TX today to see if the failsafe you mentioned was infact active. If that's the case and you were correct then the very annoying thing is its all my fault and I could have prevented it and saved my aircraft. If I had put the throttle up and back down during the flight it would have been able to land!! Gutted slightly... Quote Link to comment Share on other sites More sharing options...
Mark a Posted July 27, 2014 Share Posted July 27, 2014 For the sake of 20 or 30 quid I tend to change my RX packs on regular basis. I bin mine once they start to show a bit of fatigue and is money well spent for continued safe flying. Mark. Quote Link to comment Share on other sites More sharing options...
Paul Marsh Posted July 27, 2014 Share Posted July 27, 2014 Don't have to spend £30 on a battery, I get mine from here: **LINK** Also, if the battery goes flat the failsafe won't work. Really the wall chargers which come with the radios are no good. If the battery has reduced capacity, you won't know until it's too late. Someone at the club doesn't own a charger, just uses a 50mah wall wark job. Was surprised when I checked his battery and it only had 25% left in it. Still won't buy a charger, stubborn chap. ( I now check his battery everytime he comes- just in case). I did a thread on an old Nicad battery, which had not been used for years. Was ok, even after first charge. I was about 5% remaining. Edited By Paul Marsh on 27/07/2014 14:20:25 Edited By Paul Marsh on 27/07/2014 14:21:00 Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted July 27, 2014 Share Posted July 27, 2014 Jamie as I said earlier if your Futaba radio has the battery failsafe feature it is not user configurable - you can't enable or disable it, it's on while the radio is on. If your radio has it (and I think it does) then it will have shut the throttle to warn you that your Rx battery was dying. This was the point of my first post to you - if you'd known about the battery failsafe you could have landed immediately and saved the model instead of carrying on the flight until the battery was completely dead. That was why I asked you about your battery charging as I suspected this was the cause. It's too easy to just say "oh yeah my throttle servo must have gone dodgy and this ran the battery down and crashed the model". I wouldn't want you to then put a potentially suspect battery (as you have since proved) into another model and then have that one crash too.... Quote Link to comment Share on other sites More sharing options...
Mark a Posted July 27, 2014 Share Posted July 27, 2014 I don't spend £30 on a battery I get 3 for £30, I have 12 planes all have rx packs so just keep an on them and change them as required. Mark. Quote Link to comment Share on other sites More sharing options...
John Muir Posted July 27, 2014 Share Posted July 27, 2014 Jamie, don't get too hung up on your battery as it certainly wasn't the initial cause of your problem - it couldn't have caused your throttle to jam open. And even if you had known about the low battery warning it couldn't do you any good under the circumstances as you couldn't get the throttle shut to land anyway. If the battery had been in better nick it would, maybe, have allowed you to keep flying until the fuel ran out, but we will never know one way or the other. The battery might have been in perfect condition before your flight and was simply completely flattened by a stalled servo. I once put a model into my car with the receiver still turned on (trying to get out of the rain) and it slid back in the car pushing the rudder full over. By the time I got home about twenty minutes later, not only was the 2100mAh pack flat, but it had produced enough heat to distort its wrapping and melt the insulation on the connecting wires. I'd still ditch that battery, it's old, might never be 100% again and a new one doesn't cost a lot so it isn't worth the risk. It isn't possible to know exactly what caused this incident so I wouldn't worry too much about it. All the bases have been covered and all you can do now is check and double check everything on your next model to make sure everything is working properly before you fly. John. Quote Link to comment Share on other sites More sharing options...
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