Hi everyone! As you may have seen from my YouTube channel and Twitter page, I have built a working smoke generator for my gauge 1 Percy replica model. I was, and still am, planning to create a long-detailed video explaining the process of how I designed and built it, but I've been experiencing several inconveniences that have been preventing me from working on the video in a timely manner. So in the mean time, I decided to give a shorter explanation here that explains the major steps I took toward creating the mechanism. (Technically this is giving a lot of the spoilers for the video, but what else can I do?)
To start, there are two major parts of the smoke mechanism – the smoke generator itself and the pump. Let’s talk about the pump first.
The air pump is a micro piston diaphragm pump I purchased from eBay. While it doesn’t appear to have a brand name, you can find it listed as “JQB2838 DC 12V High Pressure Micro Piston Pump” for about $8 USD. I found that it works really well and it’s the perfect size for gauge 1 models. The main downside to using this however, would be that the rubber diaphragm piece is a very thick rubber, which may cause strain to an engine’s drive motor (Personally I haven’t experienced any major issues from it, but I just thought I’d put that out there as a note of caution).
The pump works using a crank arm and flywheel the create air movement. When the crank arm reaches the outward end of its stroke, it moves the diaphragm outward and air (or smoke in this case) is sucked inside the diaphragm through an inlet valve. When the pump moves to the inward end of the stroke, it discharges the air/smoke through the outlet valve. This combination of suction and discharge makes the air/smoke move in pulses, essentially creating the “puffing” effect!
I modified the pump by first removing the motor that came with it. I then removed the flywheel from the motor and attached it to a 2mm metal rod.
I then made a base and post for the flywheel and axle to stand on.
After that, I attached a gear to the axle. The gear has a 0.6 module so it can work with Märklin gears. Originally I used a gear that had 40 teeth on it, but after operating the mechanism I found it made Percy puff too fast for my preference, so I replaced it with a 46-tooth gear to achieve an exact 3:1 puffing ratio (for every complete wheelturn Percy makes, he will create 3 puffs of smoke).
I then attached the pump by gluing it in place. Later down the road, I decided to instead screw it place as I was having a hard time finding a glue to secure the pump to the base.
Now let’s talk about the smoke generator itself. The generator is basically a small reservoir that contains the heating element. I made my reservoir by building a simple box that fits inside the BR80 chassis and lined the insides with brass sheeting to avoid the heating element from directly touching the plastic.
The heating element is composed of a nichrome wire (found in soldering irons, wire foam cutters, and soldering irons) coiled around a fiberglass wick. The wick is saturated in smoke fluid. When power is applied to the nichrome, it heats up the wick and the fluid turns into smoke.
While the heating element still makes the reservoir hot, it doesn’t damage the plastic as the brass lining serves as a barrier.
The entire mechanism is connected together using a series of standard airline tubing (5mm diameter if I recall correctly) and plastic tubing connectors. This material can be found in pet stores in aquariums or can be purchased online like eBay or Amazon. I have one connected from the smoke reservoir to the inlet valve of the pump (Initially I used a plastic connector, but found that it kept melting from being so close to the heating element, so I replaced it with a brass tubing connector I 3D modelled in TinkerCAD and then printed through Shapeways). Then I connected a longer tube piece from the pump’s outlet valve to Percy’s smokebox.
After putting everything together, I found that this design of smoke mechanism actually works! I then moved on to convert Percy to DCC primarily so that I would able to operate the heating element at full power no matter what speed the engine would be running.
When converting to DCC, I did some research online and found that you can’t really wire a smoke unit directly to a decoder or it will burn out. So I used a bridge rectifier to convert the AC signal in the DCC track to plain DC (ONLY FOR THE SMOKE UNIT) and wire its inputs to the power pickups. The outputs of the rectifier go to the ends of the nichrome wire. This allows the smoke unit to get its power from the track instead of from the decoder, preventing the decoder from burning out.
I originally was planning to use a DPDT relay switch so the smoke unit could be turned on and off using the DCC decoder. I wasn’t able to find a good relay that worked for my application, so instead just scrapped the idea and used a manual on/off switch for the smoke unit that can be accessed from Percy’s cab.
The decoder I use is a Digitrax DG580L. It is a 5-function decoder made to handle the amp draw of G-scale motors, but works with Marklin gauge 1 motors just fine. I only needed to use 3 functions total for my Percy (Drive motor, lights and smoke). The only problem with it is that it’s a discontinued decoder, which is a shame because the newer decoders that are out on the market now are more expensive than the DG580L. There also was another one called the DG380L, which is practically the same as the other one, except it’s a 3-function decoder which is sadly also discontinued.
And that’s practically how I made the smoke unit in a nutshell! There are a few “trial and error” moments that I didn’t mention because I didn’t want to make this post longer than it already is. But more or less, the smoke mechanism actually does work and I’m super happy with the results that came with it! Feel free to reach out to me for any further questions, and be on the look out for the full video on the smoke mechanism!
