Paul Marsh Posted March 23, 2015 Share Posted March 23, 2015 Have you checked the rx xtal type, not the frequency? "xtal" means Crystal - short for. Edited By Paul Marsh on 23/03/2015 21:03:39 Quote Link to comment Share on other sites More sharing options...
ChrisB Posted March 23, 2015 Share Posted March 23, 2015 I would strongly suggest you join a club and get face to face assistance. Where in the country are you? It sounds like an installation problem. If you have a second RX, switch, battery and servos, try them on a bench to see if the same thing happens. Quote Link to comment Share on other sites More sharing options...
Stephen Tye Posted March 24, 2015 Author Share Posted March 24, 2015 East Sussex,. will take closer look and try the various suggestions when time allows.. cheers for the advice. Quote Link to comment Share on other sites More sharing options...
gangster Posted March 24, 2015 Share Posted March 24, 2015 Stephen This needs logical investigation, there is not a simple solution that we can offer without you going methodically through the process You need to get underneath this before you even dream of flying it, As already suggested any one of the parts of the radio system can cause this. I am assuming that there is full control of the servos t from the transmitter Have you done a range check? Servos . I see no merit in changing them all connect them one at a time and observe the conditions. It is possible that the problem may not be down to any one servo but when you get 3 or more connected they may start to interact. This could be indicative of a battery, receiver or switch fault even. It is equally possible that one rogue servo could cause it. Battery What is the battery voltage doing ? Does a prolonged session (few seconds ) of stirring the sticks make things worse? I would advise buying a battery monitor, even a cheap on board one( for a few pounds ) is something you should have anyway. Receiver Could be the culprit , substitution if really the only way, Transmitter Ditto RX What is its battery looking like? Crystals Less likely if your range check is good, but as already suggested is a very important component in the chain. Switch The weakest, most neglected and in my opinion the biggest cause of radio failure going, if left connected to the battery for long periods of time susceptable to black lead corrossion and general festering. They are also , regardless of radio make, crap quality. If its been in a model any length of time chuck it they are cheap as chips. As suggested earlier you may need help especially substituting and thats where the club comes in. There may even be someone on this forum near you. Test methodically and come back with the results to the forum. Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted March 24, 2015 Share Posted March 24, 2015 Gangster's list of checks is spot on . However, when I've had this sort of 'is it / isn't it' issue in the past on 35 meg gear, I've had the TX drive two sets of RXs, batteries and servos, side by side, in order to really nail the problem area. If both receiver installations exhibit a problem simultaneously, then the issue is external to them - if only one of the two shows the fault, then that lets the TX off the hook. Edited By Cuban8 on 24/03/2015 10:02:50 Quote Link to comment Share on other sites More sharing options...
kc Posted March 24, 2015 Share Posted March 24, 2015 Check the items suggested by Gangster and in addition check that the Rx crystal is marked 'Dual Conversion'. One of the advantages of being a club member is the advice and knowledge available. But in this case the advantage would be even greater because many club members have good 35 mhz gear standing idle and it is likely that someone would offer the loan of a Futaba TX & Rx and crystals to allow substitution of components to be made. Most clubs allow prospective members to attend a few times ( if you are BMFA insured ) before actually demanding fees Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted March 24, 2015 Share Posted March 24, 2015 Hi Stephen I see that you are using JR servos. They should only be used with a 4 cell NiMH pack - max of 6 v when fully charged. If you are using a 5 cell NiMH pack then the over voltage applied to the servos could be the cause of the twitching. I had that happen once with a Spektrum servo but those ones were merely re-badged JR ones and exhibited the behaviour you have described. If you are using a 2 cell LiPo then you must use a voltage regulator or a combined switch/voltage regulator to provide no more than 6 volts to the Rx/Servos. Rxs are fine with 5 cell NiMHs by the way - it's just that they pass the full voltage to the servos. Quote Link to comment Share on other sites More sharing options...
gangster Posted March 24, 2015 Share Posted March 24, 2015 Interesting point about dual conversion KC I had assumed that if you put a standard crystal in a DC receiver it simply would not work, or if if did the range would be a couple of feet. Is there something I am overlooking here ? Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted March 24, 2015 Share Posted March 24, 2015 Posted by kc on 24/03/2015 11:16:33: Check the items suggested by Gangster and in addition check that the Rx crystal is marked 'Dual Conversion'. One of the advantages of being a club member is the advice and knowledge available. But in this case the advantage would be even greater because many club members have good 35 mhz gear standing idle and it is likely that someone would offer the loan of a Futaba TX & Rx and crystals to allow substitution of components to be made. Most clubs allow prospective members to attend a few times ( if you are BMFA insured ) before actually demanding fees Prospective members would be covered by the affiliated clubs own insurance under the 3 visit rule. John Quote Link to comment Share on other sites More sharing options...
Stephen Tye Posted March 24, 2015 Author Share Posted March 24, 2015 I don't have a lot of time during the week, work comittments etc, will do a stage by stage check probably nearer the weekend. The TX does run all of the servo's flawlessly. am taking everything on board and will sort the problem out before the plane gets anywhere near a flight time. Thanks Quote Link to comment Share on other sites More sharing options...
Stephen Tye Posted March 24, 2015 Author Share Posted March 24, 2015 And yes I am a BMFA member, I havnt got the membership card through the post yet but I did it all online last week and got the email confirmation.. status is active.. Quote Link to comment Share on other sites More sharing options...
kc Posted March 24, 2015 Share Posted March 24, 2015 Gangster. Re dual conversion. All I know is that for correct operation the Dual conversion Rx needs a dual conversion crystal! Using a non dual crystal might produce much reduced range - but that is what we have here isn't it? I wonder if the Tx and Rx crystal have been interchanged? My understanding is that Tx and Rx crystals are anyway on a slightly different frequency hence in the old 27 meg days people swopped them over to get a 'new ' frequency didn't they? But we don't know the history of this set yet. Why a newcomer now has a new 35 Mhz set when it's probably difficult to buy one is a worrying point. Could be a new set just stored . Could it be some unscrupulous trader has cobbled together a set from remaining items? My advice to any newcomer or old hand is to be completly honest and open about experience & equipment when you join a club. Pretending you have experience and good equipment does not carry much goodwill with clubs when the lack of it inevitably becomes apparent! We are much happier with the newcomer who admits he knows nothing and tells us the origin of his gear. Then we can give him the best advice. We have all been newcomers once ourselves and we are all still learning. Quote Link to comment Share on other sites More sharing options...
GONZO Posted March 24, 2015 Share Posted March 24, 2015 Re Xtals, they also have to be of the same make as the Tx for the Tx Xtal. Futaba Tx will only work correctly on 35mHz FM with a Futaba Tx Xtal. Some Tx use a Xtal that resonates at second over tone and others resonate at third overtone. FM modulation pulls the nominal frequency about this slightly. The only reason you could swap Rx/Tx Xtal's over in the 27mHz days is because it was AM, not FM, and they were both third overtone Xtals. Thus, normal was Tx on the specified frequency with the Rx local oscillator resonant 455kHz lower thus giving sum and difference frequencies when both were applied to the mixer stage. The sum was too high to get through the IF(Intermediate Frequency) stage but the difference was the required 455kHz which passed through and was amplified at several stages(modified by the AGC, Automatic Gain Control) to the detector. Swapping around the Xtals caused the Tx to transmit outsde the band (lower). This is much simplified and hopfully remembered correctly as 27mHz AM was replaced by 35mHz FM, for aircraft, almost 35 years ago. HTH Quote Link to comment Share on other sites More sharing options...
gangster Posted March 24, 2015 Share Posted March 24, 2015 Yes I think that is about right Gonzo. You would certainly end up with a new frequency 455khz below The tuned circuits in the TX and RX were wide enough to still give good range in most cases. I believe you are right about the FM transmitters not allowing this due to multiplication cannot remember the sums though and am not about to take myself back outside and experiment I have already wasted half the evening monkeying around playing with A watt meter and experimenting with the percentage figures that gave after someone raised the question in the club My earlier point re double conversion was that it could not be a mix up with crystals that caused the issue in the OP I can just about believe that the wrong type (DC /SC) might work at a range of a couple of feet due to overload but no further. I really believe it is in reality not going to work at all. I am sure with logical faulting and a bit of help the issue will be sorted and it will be a fine set of radio Quote Link to comment Share on other sites More sharing options...
kc Posted March 25, 2015 Share Posted March 25, 2015 Gangster is right - a practical experiment has shown that swopping the Tx crystal with dual conversion Rx crystal does not work. Well with my Futaba T6EXP and FP R138DF anyway. That still leaves other items to eliminate such as single conversion crystal used in double or non Futaba crystal used in TX Quote Link to comment Share on other sites More sharing options...
Stephen Tye Posted March 25, 2015 Author Share Posted March 25, 2015 Upon removal of the RX Xtal found it to not be dual conversion... have the correct type and make on order... Will check the situation again when arrives. Many thanks guys!.. Quote Link to comment Share on other sites More sharing options...
Stephen Tye Posted March 25, 2015 Author Share Posted March 25, 2015 BMFA membership pack arrived... Quote Link to comment Share on other sites More sharing options...
Stephen Tye Posted March 25, 2015 Author Share Posted March 25, 2015 Going to check all the wiring and the inside of the RX just in case Quote Link to comment Share on other sites More sharing options...
Paul Marsh Posted March 25, 2015 Share Posted March 25, 2015 My post a few days ago: "Have you got the right XTAL in the receiver? The rx is Dul Conversion, what colour is the xtal?". I said it was!!! I'm brilliant... Edited By Paul Marsh on 25/03/2015 18:36:57 Quote Link to comment Share on other sites More sharing options...
GONZO Posted March 25, 2015 Share Posted March 25, 2015 I'm reminded of an old saying "self praise is no recommendation". Quote Link to comment Share on other sites More sharing options...
Shaunie Posted March 25, 2015 Share Posted March 25, 2015 Where in East Sussex are you as I'm in Edenbridge (Kent, Surrey, Sussex border). Shaunie. Quote Link to comment Share on other sites More sharing options...
kc Posted March 26, 2015 Share Posted March 26, 2015 It might be quite difficult to buy a new crystal.......but there must be large numbers of crystals and 35 mhz Rx sitting around unused now. Someone might offer you one for a modest price...... Either a single conversion Rx or a same frequency pair of Futaba Tx and a Rx dual conversion crystals will sort this out. But the real question is why was a 'new' set sold with odd crystals? The whole outfit needs to be carefully checked and range checked now. Edited By kc on 26/03/2015 11:44:55 Quote Link to comment Share on other sites More sharing options...
kc Posted March 26, 2015 Share Posted March 26, 2015 I suppose it's worth saying here that it's not worth spending any large amounts on 35 Mhz equipment now. There is nothing wrong with 35mhz of course but the sheer convenience of 2.4 ghz such as flying at a moments notice without having to check if someone else is on your frequency is invaluable. Especially when you are training. There are other benefits with 2.4ghz such as not having to remember to extend the aerial just before flying and no chance of being shot down etc, etc. So what I am saying is dont spend anything near the cost of a 2.4 combo ( about 50 pounds for the most basic like a DX5 ) on bringing any 35 Mhz set up to scratch without weighing up the pros and cons carefully. All the fancy gadgets and mixers on a once expensive 35 mhz set wouldn't tempt me away from 2.4 ghz ! Quote Link to comment Share on other sites More sharing options...
GONZO Posted March 26, 2015 Share Posted March 26, 2015 Agreed. But, you could always instal a 2.4gHz 'hack' modul in the Tx and buy a new 2.4gHz Rx. 'Robert is your mothers brother' and the jobs a good 'un! Quote Link to comment Share on other sites More sharing options...
gangster Posted March 26, 2015 Share Posted March 26, 2015 A lot of assumptions have been made here. Nothing I have read so far convinces me that the crystal has been conclusively proved to be the culprit. has a range check been done? I still believe there could be no way a single conversion would work in a dual conversion receiver . Equally if a different make of receive crystal had been fitted that might not be comparable it would not cause random servo twitching unless the range was severely impared. and before someone accuses me. No I do not advocate that it is permissible to fit an incompatible crystal into a receiver even if it works reasonable well cos it could end up sufficiently off frequency to cause adjacent channel problems. Futaba crystals are readily available still and as far as I know Futaba kept their crystals quite simple and standard unlike other manufactures eg Sanwa Suggest you post a picture or description of your crystals on here there are plenty of Futaba experts on here and will Identify what you have. As far as I know Futaba dual conversion RX rocks have orange and white labels with dual conversion written on them Quote Link to comment Share on other sites More sharing options...
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