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Offline Rad_Schuhart

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  • Graz, Austria.
Smoke questions.
« on: August 15, 2020, 12:53:27 PM »
Hi Luke, after years messing with smoke generators I am a bit stuck and I guess you know much better than me what to do.

My first Heng Long smoke generator did not last long, and back in the day I replaced the pump with a 25mm fan and the heating element with diferent resistors with tons of different values according to the results I found in google, achieving generally good amount of smoke but a super heat smoke unit, and sometimes a damaged main board.

When creating my own experiments I managed to destroy (but luckily replace) several times the transistor that controls the smoke output in an old RX18 I had. The machine that I had working in the Rx18 ended damaging the smoke port in one ASP board from RC tanks australia.

So it leads me to this point: I wish to make the smoke generator work as it should, but with no overheating and no risk to the TCB or to my Elmod board. As you can imagine damaging those boards can be catastrophic, one for unobtainable and the other for over expensive, lol.

So my question is, what resistor or what thing do you recommend me to fit in the smoke generator as a heating element? Also as a wick what do you use?

Thanks!


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Offline LukeZ

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Re: Smoke questions.
« Reply #1 on: August 17, 2020, 10:09:02 AM »
Hi Rad, good questions. I haven't done many experiments myself so I can't really give you a detailed arrangement that I know will work from my own experience. But I can tell you what the limits of the TCB are and there are also lots of good resources online.

The Smoker output on the TCB can handle at least 3 amps, which should be more than enough for whatever resistor you want to use. Typical values are somewhere in the range of 5 to 20 ohms, the lower the resistor the higher the current, but even with 5 ohms and a 7 volt battery you will only be drawing about 1.4 amps (this doesn't count the current of fan, but that is usually not very much).

As you probably saw, you now also have the option of putting the heating element on the Smoker output and driving the fan separately on the Aux output. This allows you to keep the resistor at maximum heat even when the fan is turning slowly. There are lots of options, see the Motors tab of OP Config for more. One thing to keep in mind is that the Aux output is always 5 volts so you will need to use a 5 volt fan, and try not to draw too much current on the fan (the TCB has a limit of 3 amps for all 5 volt outputs combined, that includes lights, servos, etc...) But most small computer fans draw very little. (The voltage on the Smoker output is whatever the voltage of your battery is.)

For the actual resistance it is just something you have to experiment with. The main thing is to get a resistor with a high enough watt rating that it won't burn up. To calculate watts you can multiply current * voltage. In our example above with a 5 ohm resistor at 7 volts, current is calculated to be 1.4 amps, multiply that by voltage of 7 and we get almost 10 watts. It is unlikely you'll find a resistor small enough with a 10 watt rating, you might only find a 1 watt resistor. But they can be overloaded before they burn out (in fact we want to overload them because that is how we are creating the heat). If we have a 1 watt resistor and we are pushing 10 watts through it, that is overloading it by a factor of 10. A users on RCUniverse (danlrc) years back did some tests and found the resistors would usually last fairly well if we keep the overloading factor to 15 or lower. It also helps to use a wirewound resistor instead of carbon film.

There was a really good thread years ago that you might find interesting: Heng Long Tiger Smoke Unit Repair and Mod

For wicks some guys just use strips from an old cotton t-shirt. Or if you want to get more fancy you can use kevlar string or wick, they talk about that in the same thread.
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Offline Rad_Schuhart

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  • Graz, Austria.
Re: Smoke questions.
« Reply #2 on: August 18, 2020, 03:20:46 AM »
Hi Luke, thanks for the answer.

The thing is I have been experimenting for years with smoke machines with mixed results. I think I have tested every thing I have read in forums, including the thread you already linked me. Those wirewound resistors, normal resistors, a piece of a hairdryer... Last thing I tested last week was almost what is showed in this video:
But instead a 0.5W I tried with 0.25 and with 1W and with both cases after a while I got heaps of smoke, but the plastic enclosure was horrible hot, almost untoucheable, that even melts the hoses. Also with the bluetooth Elmod app I could see a voltage drop of about 2 volts when the smoke generator was running. Definitelly this does not sound like the way to go. I seriously even wonder if all those threads are from people that tested the smoke machines for 30 seconds instead of running them for longer times.

As mentioned above, I blew the RX18 several times, but when I managed to have a working machine, it blew the smoke output in my ASP board. The smoke machine never worked fine with that board, not even the stock one, so I guess it was more of a board issue. Repairing it was a pain by the way (attached pics)

After the ASP experience last thing I want to is to damage any of the other boards, so I decided to ask everybody. The answers I got so far are:
the one you wrote us. (thanks again, by the way!)
Kevin from RC tanks australia does not recommend any resistor but nichrome wire, about 20cm long, but with unknown thickness. (not knowing the thickness is critic, the thicker it is, the shorter it will be!)
Ian, distributor of IBU said that the TARR Smokers they sell use a small wound metal element which is about 15ohms resistance, and the IBU smoke port is capable of 1Amp.

I will ask also Elmod and Clark. Great think the niche of this hobby is so small that everybody is reacheable, lol.

Anyway I really wonder if there is a definitive answer. It is like the TARR smokers, some people says they produce heaps of smoke and some other say they produce almost nothing or none at all. I really do wonder why so many mixed answers everywhere, besides using different smoke fluids.

By my side, I dont nead a smoke curtain, just something that is visible and does not burn itself or damages the board. Sometimes is hard to know if the smoke machine is working or burning, lol.

Anyway, I will update the thread with all the experiments. I guess somebody can find this useful.
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Smoke questions. IMG_20190109_191919.jpg
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Smoke questions. IMG_20190109_180827.jpg
Views: 43

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Offline JPS99

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Re: Smoke questions.
« Reply #3 on: August 18, 2020, 03:41:50 PM »
I bought a V6.0 Heng Long smoker on Ebay recently and is working pretty well. They seem to have done some improvements on the unit as several mods I read about on the forum that Luke mentioned above https://www.rcuniverse.com/forum/rc-tanks-369/5806555-heng-long-tiger-smoke-unit-repair-mod.html

I think most of those guys are running  14 to 18 ohm resistors, preferably wire wound.

On my unit, I added a 5 volt fan to improve the airflow through the unit.  Got the info here: https://www.rctankwarfare.co.uk/forums/viewtopic.php?f=33&t=8027


That helped improve the smoke from the unit, but kept the pulsating effect that you get from the piston air pump.

This is how I mounted the fan:   

I found my best improvement was to run Johnson's baby oil in the Heng Long and to route the smoke tubes as direct as possible to avoid kinks, bends, etc.
You can see the improvment here: 

I think it is easy to waste a lot of time on smokers, at least I sure did!  I'm pretty happy with it now. I can run it for 20 minutes or so with 3ml of baby oil in it on my 3D printed IS-1 tank .






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Offline Rad_Schuhart

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  • Graz, Austria.
Re: Smoke questions.
« Reply #4 on: August 19, 2020, 01:12:23 PM »
Thanks for your experiments, JPS99, I apreciate every info :)

At the very beginning of my hobby I managed to do this video:

That machine is running with an old heng long RX18 with an RC5HL adaptor for hobby grade radios.

I always run 12V fan because when running 5v I found they push way too much air on the unit, so the smoke leaves the exhaust with way too much pressure. Also the fans end burning too. With 12V fan I never had a problem.

It worked good enough, but after a while it gets very hot. I ended wiring it to an external ESC and controlling the voltage with a potentiometer in the radio. But still I am triying to make the ultimate smoke machine, lol

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Offline JPS99

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Re: Smoke questions.
« Reply #5 on: August 25, 2020, 09:33:26 AM »
No, they won't smoke much on 5 volts.  I run a 2S Lipo in my IS-1 so my max voltage is only going to be somewhere between 7 or 8 volts with the tank moving.
I'm not looking for huge clouds of smoke, but I definitely want to see realistic exhaust smoke when idling and driving.
The Baby Oil works well and smells nice. When I see smoke coming out of the filler tube I know it is time to add another 3ml of oil.

 

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