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Author Topic: A variation on smoke generator design  (Read 4398 times)

nsa66

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A variation on smoke generator design
« on: December 23, 2011, 10:43:52 AM »

This is a little smoke generating unit that I came up with for my TID tug refurbishment project.

It uses a 15 Ohm ceramic-clad wire-wound resistor (69p at Maplin) as a heating element. This draws approximately 800mA at 12V giving a wattage of 9.6 which compares well with the resistorís maximum rating of 10W. The resistor sits on a paxolin plate which in turn rests on a few layers of woven heat-resistant fabric, several strands of which have been teased out and wrapped around the resistor to form a number of wicks. The (black) fabric was bought from Screwfix as a fireproof mat to be placed behind copper pipework when soldering with a blowtorch. Its wicking properties are excellent Ė better than the woven glass matting Iíve used for similar purposes in the past. The thick layer of matting absorbs a good amount of fluid Ė enough to operate the unit for at least an hour. Overfilling is not recommended as any fluid which comes over the paxolin plate will cover a relatively large area of the ceramic element and lead to cooling and reduction in smoke output. It is easy to determine by trial and error just how much fluid should be added once the generator stops smoking. If not overfilled the matting overcomes any tendency for the fluid to slosh around without the need for any baffling.



(Click to Enlarge)


I have tried various ďfuelsĒ including WD40 (OK but maybe a bit too volatile), Ethylene Glycol (less good and toxic) and lamp oil (good but expensive locally). Baby Oil works very well and the supermarket own brand stuff is pretty cheap. Iíve had it suggested that diesel itself might work and Iíll probably give it a try Ė it can always go straight into the car if itís no good.

The idea of using a ceramic resistor was to provide a constant heat source without having excessive localised hot spots that have always made me wary of home-made hot wire devices, which also seem to create a lot of charring. Keeping the wattage within the resistorís limit should also ensure the longevity of the element. The down side to this is that there is a large body of material to heat up before the element is hot enough to work. It takes around 5 minutes of pre-heating to achieve smoking temperature but this can be reduced somewhat if the fan can be separately switched off. Smoke volume can be controlled to a degree by varying the amount of wick material in contact with the resistor. To make a real increase in volume it would be necessary to add extra resistors in parallel with the first, obviously at the expense of increased current flow.

By having the element permanently heated and using the fan to modulate the smoke flow, the unit is very responsive indeed Ė even when large runs of exhaust pipes are used. I have tested it with over 1m of garden hose on the outlet and it only takes a couple of seconds for a steady stream of exhaust to appear whatever the orientation. This suggests that it would make a good unit for any model with horizontal exhaust outlets or a funnel which has to be located remotely from the generator. To simulate a slower, broader flow such as an oil burning boiler, simply exhaust the narrow exhaust pipe into a wider one. The longer, smoother and straighter the final section of flue, the more linear the exhaust plume will be before turbulence causes it to billow out. Obviously a faster fan speed will also result in a longer initial plume.

On my tug, fan control is to be be accomplished as follows:  A servo carrying an output disc is connected in parallel with the speed controller. Notches filed into this disc control a pair of microswitches. The first microswitch/notch is arranged to supply power to the fan only when the throttle is moved sufficiently away from centre to start the propulsion motor. The fan is connected to this microswitch via a 22 Ohm resistor which allows a slow fan speed and therefore a relatively dense emission on start-up. Advancing the throttle (ahead or astern) beyond approximately half speed causes a second microswitch to short across this resistor, allowing the fan to run at full speed. This simulates the higher velocity and sparser exhaust of a diesel running at high speed. The beauty of this system is that if the vesselís engine has been idle for a short length of time there will be a momentary increase in smoke density as the revs are increased. It would work particularly well for a vessel with a direct-reversing engine.

The only snag when using the fan to control output is the tendency for smoke to escape through the inlet duct by convection when the fan is not running. A bit of experimentation with air intake cowlings reduced this to a bare minimum, certainly not enough to fill the hull with dense fumes. In most applications there would be little time when the fan is not actually running.

On a final safety note, I have left the unit with the heater running and the fan switched off for up to an hour. The unit becomes warm to the touch but not worryingly so. The hottest area is on the base of the enclosure, suggesting conduction of heat through the paxolin and oil-impregnated matting. The paxolin serves only to keep the body of the resistor away from the wetted matting in the base of the enclosure. It is likely that some sort of suspension could be devised which would keep the heater clear of the fluid and cut down on such heat conduction. Iíll try something of the sort next time, but this prototype is so effective as it is that there is no real need to mess with it. Using standard silicon sealant to attach the unit would be fine. Running the fan, even at low speed cools the unit rapidly and considerably.

Iíll try and get some video once the tug is on the water but if anyone wants to try something similar Iíd be happy to hear about it.


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john44

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Re: A variation on smoke generator design
« Reply #1 on: December 23, 2011, 12:03:08 PM »

Excellent nsa66,
Cant wait to see the vid. In or out of the boat.
Where did you get the dicast case from?

john
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nsa66

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Re: A variation on smoke generator design
« Reply #2 on: December 23, 2011, 02:03:20 PM »

Hi John,

The enclosure came from Maplin (cat. no. N88BQ) and cost around £4.00.  Next time, however, I'll try and find one that's a bit deeper and shorter - more cubic if you like - to allow more capacity, a smaller footprint, and slightly more space above and below the resistor. Failing this I'd still be happy to use the same box and repeat the same basic design, maybe incorporating some sort of baffle beneath the fan to stop smoke convecting upwards with the fan off.

Cheers

Neil
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Bill D203

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Re: A variation on smoke generator design
« Reply #3 on: December 30, 2011, 11:52:26 AM »

Well Thats just what I wanted, so I set about making one this morn. It works OK but I would like the smoke a wee bit blacker ! Any idears on how to do do that???
http://www.youtube.com/watch?v=OGm3v4ht8eY&feature=youtu.be
Still not a bad start i think :-))
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john44

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Re: A variation on smoke generator design
« Reply #4 on: December 30, 2011, 04:07:51 PM »

following with great interest O0

Bill are you going to use a speed controller for the fan?

john
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Bill D203

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Re: A variation on smoke generator design
« Reply #5 on: December 30, 2011, 05:49:48 PM »

following with great interest O0

Bill are you going to use a speed controller for the fan?

john

Hi John
I'm using a variable voltage reg to control the fan speed. Since I took that video this morn I have fitted a deflector plate to so the fan dose not blow directly on the resister which helps I found if you give it 14.2 volts from a Lipo pack it works alot better. In the video i used a drill pack for the resister and 8.4 nicads for the fan. Now it all runs from the Lipo's. I hope to be able to control the via a RC switch as and when i get one from Action electronics
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ACTion

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Re: A variation on smoke generator design
« Reply #6 on: December 30, 2011, 05:50:43 PM »

This will do the job - saves a lot of mucking about. The latest version has a fan which runs very slowly at zero throttle and accelerates as throttle is increased, so there's always a small positive pressure pushing the vapour up the spout. It runs from the receiver supply, in parallel with the ESC for the main motor, so no extra wiring or separate power supply required.
http://www.action-electronics.co.uk/pdfs/P68S.pdf
DM
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Bill D203

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Re: A variation on smoke generator design
« Reply #7 on: December 30, 2011, 07:12:35 PM »

This will do the job - saves a lot of mucking about. The latest version has a fan which runs very slowly at zero throttle and accelerates as throttle is increased, so there's always a small positive pressure pushing the vapour up the spout. It runs from the receiver supply, in parallel with the ESC for the main motor, so no extra wiring or separate power supply required.
http://www.action-electronics.co.uk/pdfs/P68S.pdf
DM


Nice one Dave
However I need my smoke to come on when the engine in my Fishing boat blows up!!! Then My Life boat come out to rescue the fishing boat.
But I do like your unit and for thems that want a the smoke related to speed then thats just the jobby mate.
PS Did you have a good Christmas? Happy New Year.  :-))
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bismarck builder

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Re: A variation on smoke generator design
« Reply #8 on: December 31, 2011, 09:47:01 AM »

hi
are you going to sell them??
how much??
can i have 2
cheers
gary
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Martin [Admin]

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Re: A variation on smoke generator design
« Reply #9 on: January 01, 2012, 01:50:42 PM »

This what we need!  ok2

http://youtu.be/qKg-LPOXIMs
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john44

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Re: A variation on smoke generator design
« Reply #10 on: January 01, 2012, 04:42:02 PM »

This what we need!  ok2

http://youtu.be/qKg-LPOXIMs

I agree totally Martin.
 So if there is anyone out there who knows the maker of the smoke units?
Tell them to get in touch with the forum and show us how its done. {-)

I bet they cheated and used dry ice. O0

john
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Bill D203

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Re: A variation on smoke generator design
« Reply #11 on: January 01, 2012, 06:14:53 PM »

This what we need!  ok2

http://youtu.be/qKg-LPOXIMs

That 2 stroke food mixer is the biz. I'm off to Currys to get her one. :}
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alan rushbrook

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Re: A variation on smoke generator design
« Reply #12 on: January 02, 2012, 07:31:56 AM »

Never mind a little 2 stroke think big
http://www.youtube.com/watch?v=vDlMLqdvHzI
All the best and a happy new year
Alan R
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alan rushbrook

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Re: A variation on smoke generator design
« Reply #13 on: January 02, 2012, 07:34:49 AM »

Sorry about the advert, i do not know how that got in on the act

Alan R
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Bill D203

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Re: A variation on smoke generator design
« Reply #14 on: January 02, 2012, 01:23:32 PM »

Here's Mk2
I have put smaller fan in it so it dose not chill the resister down as much.
http://www.youtube.com/watch?v=W1Cl47tSfoI&feature=youtu.be
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malcolmfrary

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Re: A variation on smoke generator design
« Reply #15 on: January 04, 2012, 11:02:52 AM »

At about 42sec into the ad, they explain very neatly why we dont use electric cars - recharging the POS card reader from a tiny jerry can is much faster than recharging a battery.

When I tried making a smoke generator a few years ago, I came to most of the same conclusions regarding the resistor.  It didn't use a fan, and the wick was candle wick from the craft shop.  This produced its ow smoke as the fog oil ran down.  The reservoir I made from fireclay having poked holes in the ends for the wires and then baked in the oven.  This made a liquid tight open box that I could hang the resistor in.  No problems with the wires shorting to the case - fireclay is a good electrical insulator.
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