mfin Posted March 2, 2009 Share Posted March 2, 2009 Hi all. Tried a test on my saito 100 which has a pitts smoke muffler today, was always under the impression that 4 strokes won't make much smoke but blew a bit of diesel down some tubing to try it and it worked quite well, thats without any pre-heating copper coils round the muffler or anything. So, things can only get better. Anyway, does anyone know a cheap and cheerful pump that I can use, I understand the principals... Pete Tindalls seems best value at £80 and £99 gets a Sullivan Skywriter but these seem a bit over the top for me, anyone know a cheaper way? I know both of these offer throttle coupling and so on but a lightweight pump that would run on 6v would be fine I reckon for a basic system. Anyone tried anything or know of anything?? And, where would I find a remote switch to control one off a receiver channel? Did think of a basic fuel pump like http://www.sussex-model-centre.co.uk/shopexd.asp?id=13913 ???? Quote Link to comment Share on other sites More sharing options...
mfin Posted March 2, 2009 Author Share Posted March 2, 2009 By the way, I have an old 25 amp ESC from a park flyer lying around, surely that would control a flight box fuel pump or something? Got to keep the spirit of bodging alive? I'll put another battery in there just to run it so I don't end up with no electrical juice left for the servos after running it !!! Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 3, 2009 Share Posted March 3, 2009 You can use the circuit board from any old servo as a switch. Just wind the pot to one end and use the motor drive connections to operate a small relay. The servo circuit will see the operating arm of the servo as being at one end of its travel and continuously drive the motor to try to send it to the other end if you program a switch function (like retracts for example) on that channel. Putting the pot at the other end of its travel will reverse the function. It would also be a good idea to put a diode (something like a 1N4001, cathode - the marked end - towards the positive feed) in parallel with the relay to limit inductive spikes from switching the relay coil. Quote Link to comment Share on other sites More sharing options...
Jimbo565 Posted March 3, 2009 Share Posted March 3, 2009 Try Just Engines and Pyramid models,they both do smoke systems and you may find what you are looking for. Jim Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 3, 2009 Share Posted March 3, 2009 Great idea Martin - and a system I have used too and works fine Just a small point to the OP - in case you try it, and aren't too savvy with the old black art - Martin means ( I assume ) that the diode should be connected across the relay COIL not the contacts! Quote Link to comment Share on other sites More sharing options...
mfin Posted March 3, 2009 Author Share Posted March 3, 2009 Thanks all. Can't find my ESC (thats that adventure out the way then) so it now looks like its an experiment with a fuel pump and taking a servo apart - my kind of fun - or find a reasonable cost electric pump smoke system off the shelf (just engines seem perry pump based instead, too many variables in my mind). Not missing any systems am I, I can see the one mentioned at Pyramid Models, the Sullivan Skywriter and the Pete Tindall system ...I must admit I thought something so basic in principal would be cheaper myself. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 3, 2009 Share Posted March 3, 2009 Martin means ( I assume ) that the diode should be connected across the relay COIL not the contacts! Quite so, Timbo. Quote Link to comment Share on other sites More sharing options...
Terence Lynock Posted March 5, 2009 Share Posted March 5, 2009 Couple of weeks back someone flying a Corsair was leaving a lovely trail of blue smoke behind him, pity it was an electric.... regards, Terry Quote Link to comment Share on other sites More sharing options...
Chris Channon Posted March 5, 2009 Share Posted March 5, 2009 Hi, i have used a standard glow fuel pump running off a 4.8v rx pack, it works well. By using a 12volt pump on 4.8 it runs slow and pumps enough smoke oil through with good effect. Regards Chris Quote Link to comment Share on other sites More sharing options...
mfin Posted March 5, 2009 Author Share Posted March 5, 2009 Ah Chris, thats my kind of thinking, I'd also thought if pressure was a bit high I could use a little more fuel tubing to make the pump not shift as much. Gotta try this, I understand I'll need a non-latching relay and another battery to drive the fuel pump.... this using a servo as a switch business, are people saying then that you leave the motor and everything in the servo, get the cogs off the the top and turn the pot to the extreme then the motor will drive constantly when fed the right signal THEN piggy pack my relay control off the back of the motor's terminals? OR are we saying strip a servo apart and leave pot connected to the circuit board and you can just put the relay across the motors terminals instead of the motor. I just don't quite understand the servo as a swicth in laymans terms yet. Even have a relay in the house that'll work so this could be done with stuff I've got lying around! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 5, 2009 Share Posted March 5, 2009 You dont need the motor at all - just the PCB. Connect the2 x wires that would normally have gone to the brushed motor to the relay coil ( use a low voltage low current requirement relay ) Yes you need to remove the feedback cogs and then turn the potentiometer to the end of its travel - be careful not to force it past the end stop - and then on signal from Tx the relay should activate. The relay coil is not polarity concious ( but the blocking diode if fitted is ) You may also want to consider a diode across the pump motor too for the same reason The servo itself is not the switch - thats the relays job..all the servo guts are doing is reacting to a TX command, and energising a relay coil, instead of a servo motor Geddit? Quote Link to comment Share on other sites More sharing options...
mfin Posted March 5, 2009 Author Share Posted March 5, 2009 Think so, just pulled a couple of real old junk ones apart and tried with no motor and it seemed to fry the board (after working fine piggy backed off a spinning motor) whilst I was just had a multimeter across to check the voltage was still there. Was I unlucky, perhaps I had shorted something accidentally? Hmmm... piggy backed another and it works like that. Dare I try unsolder the motor connections again on this one??? Quote Link to comment Share on other sites More sharing options...
mfin Posted March 5, 2009 Author Share Posted March 5, 2009 Ahh.... tried it, works fine with this one... so... seeing as 6v is my actual fligh pack does this relay look right?? http://www.maplin.co.uk/Module.aspx?ModuleNo=218089 ...I only have 12v ones here and they are on the brink of reliable operation with a good 9v battery so they won't be much good I don't think. Quote Link to comment Share on other sites More sharing options...
mfin Posted March 5, 2009 Author Share Posted March 5, 2009 Right, now sorted relays too, just was getting lazy. I don't suppose anyone knows if any fuel pumps are lighter than others, its not something you consider when you're putting it in a flight box! When I've got this working I'll post some videos. Quote Link to comment Share on other sites More sharing options...
mfin Posted March 5, 2009 Author Share Posted March 5, 2009 Ummm... anyone seen one of these in the flesh? http://alshobbies.com/shop/lookupstock.php?pc=3763&Desc=pump wonder if its any lighter than say a standard orange Irvine one? Quote Link to comment Share on other sites More sharing options...
Chris Channon Posted March 6, 2009 Share Posted March 6, 2009 Blimey !!!!!! Just try the fuel pump !!! No relay, no mucking about, just smoke ! Wonders if I am allowed to say go and have a smoke ?????? Regards Chris. Quote Link to comment Share on other sites More sharing options...
mfin Posted March 6, 2009 Author Share Posted March 6, 2009 Sorry Chris are you saying just connect it to the flight battery or chuck it in and not have it turn on and offable??? Either way is not quite what I want. Timbo and that, got a couple of relays, one looks too tiddly as its only rated to go to 2A/24VDC which isn't a lot, its slightly smaller than half an oxo cube... The other one I can see the wires inside look more like it and that one is 2x1x2 cms in size and will cope with 8A/240VAC so it would be fine and is only the size of a mini servo. BUT!!!.... I wired it up and checked it, (just using multimeter set to beep at circuit across the outputs) and whilst it works fine in the first instance it soon drops my 6v battery down to early 5s and the relay starts buzzing as the volts cant hold it anymore. I don't get that, I can't see how it can drop so quickly (or do they normally drop quickly from being used)... perhaps my relay's not sapping anything much out of the ordinary at all and I just need a relay that'll behave down to 4volts or something? I can't see how a relay that requires 6v DC to operate could draw that much current, or is the modified servo doing it? I'd expect to feel heat everywhere or something? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 6, 2009 Share Posted March 6, 2009 The modded servo circuit will not be using any more current than it would normally - however the relay as load instead of the motor is obviously drawing a little too much current by the sound of it. Could you insert the MM into circuit of the relay coil and check the current drawn? It may be that you are better off using a sepearate small pack to drive that seervo /relay to preserve the integrity of the main battery. Quote Link to comment Share on other sites More sharing options...
mfin Posted March 6, 2009 Author Share Posted March 6, 2009 Ah, I see, but if I ran a separate battery for that, which would be no problem at all then which of the three wires on the servo would I have to connect to this battery. Cos of course at the moment its all just coming from the receiver isn't it. You lost me a tiny bit! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 7, 2009 Share Posted March 7, 2009 Think of like a retract servo which are often seperately powered. This old diagram here may help. Quote Link to comment Share on other sites More sharing options...
mfin Posted March 7, 2009 Author Share Posted March 7, 2009 Ahh... thats a useful thing to know Timbo, I couldn't imagine how that would have been done till I saw it. Maybe I'll have a little experiment with that and use that same 6v battery to run the smoke pump. If the voltage drops to a certain level the relay will only stop anyway so nothing critical will happen. I quite enjoy tinkering with stuff like this. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 7, 2009 Share Posted March 7, 2009 I must say that although the old modified servo / relay idea works reasonably well, I do use a more modern electronic switch system these days when required. I used to make up a nice little opto isolated proportinal unit for onboard glow drivers - and have 3 of these on my IC powered spitfire - one for the glow, one for guns, and one for landing lights. Another old fashioned system for onboard glow switches would also do what you require is the servo activated microswitch - they were a bit troublesome and could be a fiddle to set up reliably, but for a non critical thing like a smoke pump might be worth trying. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 7, 2009 Share Posted March 7, 2009 Or.... heres an older design of a simple R/C on off switch from Ken Hewitt way back in RCME 1996 - I have the text of the construction here too somewhere - very simple this one as it all gets done on a small strip of veroboard. Quote Link to comment Share on other sites More sharing options...
mfin Posted March 7, 2009 Author Share Posted March 7, 2009 Hi again. Well, digging through I 've simplified things potentially. Ive got an RC Line Soft Switch (18A) here and have wired this up and it drives it fine. It has battery + and - (ive put a 6v batt on) and motor + and - (obvious) and its servo lead to go to the receiver BUT... theres always a problem isnt there!!! ...when its plugged into the receiver it's the Soft Swtich's battery (the one connected to its battery terminals) that powers the receiver and the rest of the servos through being plugged into channel 5! If I then plug my existing battery into the reciever as well it all gets confused and doesn't work, not that I thought it would. SO... how do I modify the servo wires to the Soft Switch so that it still gets the right signal from the receiver to tell it what to do but doesn't try to give it power?? Diodes or something or cutting wires? Any pointers? I'll have this in the air tomorrow weather permitting if this is something that can be solved easily. Quote Link to comment Share on other sites More sharing options...
mfin Posted March 7, 2009 Author Share Posted March 7, 2009 Ahh... GOT IT!!! Snip the red wire, the world didn't end and everything seems to be behaving perfectly (watch this space). I found that the thing has a BEC (Battery Elimination Circuit) in it and you can disable this by disconnecting the red servo wire to the receiver. Right, bit of plumbing now and I'm away, I'll post back when its done and tested. Thanks to all so far !! Quote Link to comment Share on other sites More sharing options...
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