I posted about my SP Daylight Locomotive with a Seuthe smoke generator in this thread  a few weeks ago:

I haven't been happy with the Seuthe unit though as it leaves a little oily residue behind and doesn't run very long. After seeing this thread:

 

I've been experimenting with a similar ultrasonic mist generator using just water as the working fluid. I purchased it on Amazon, which uses a 16mm disc: href="https://www.amazon.com/gp/product/B073322QF8/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&amp;psc=1" rel="noreferrer nofollow">www.amazon.com/gp/product/B073322QF8/ref=ppx_yo_dt_b_asin...</a>

It's powered by the locomotive batteries with the control board mounted in the tender. Using a 3D printer to make the reservoir and stack, I finally got a reliable working device, which has a 4x5 stud footprint:

Here's some of the iterations it took to get it working:

Here is the final design in action:

The unit fits in a cavity I created in the front of the locomotive ahead of the drive for the air pump:

Here's the finished application. Note I did have to modify a tile and some headlight bricks to make it fit:

A cover lifts off to access the water reservoir. It holds about 9ml of water, enough for more than 8 minutes of operation. This is a stationary test of the system:

Finally, in operation:

Just like a real steam locomotive, it leaves water behind wherever it runs!

Dave

Very nice! 

Amazing stuff, you keep pushing the limits and it looks great.

Thank you both. When I was a kid, I wished for but never got a Lionel steam engine with smoke, hence my obsession to make it work here.

Dave

Hi, I love the look of your engine and the smoke effect is great. I was actually looking into doing this after I discovered these ultrasonic humidifier devices and was happy to find someone else had tried them out for this and they worked well. I was wondering if you have the 3d print files publicly available. I understand if not as it looks like a lot of work went into it, would just be very useful to me trying to make my own version. Anyway great post, it convinced me to finally make a eurobricks account after lurking for a while specifically to ask this question.

I was just about to suggest adding coloring to your water supply to aid in seeing the smoke effect, after watching your video see you have already thought of this.  Adding sound and steam effects into your build is a great effort and your results look fantastic.  Very well done!

On 3/30/2022 at 8:59 AM, albiorix said:

Hi, I love the look of your engine and the smoke effect is great. I was actually looking into doing this after I discovered these ultrasonic humidifier devices and was happy to find someone else had tried them out for this and they worked well. I was wondering if you have the 3d print files publicly available. I understand if not as it looks like a lot of work went into it, would just be very useful to me trying to make my own version. Anyway great post, it convinced me to finally make a eurobricks account after lurking for a while specifically to ask this question.

Thanks for your positive comments. I'm not sure what I want to do with this design element, I've thought of marketing it but I don't feel it works well enough yet; on occasion, it stops for a few seconds and restarts and I haven't troubleshot it to understand why. So I am reluctant to share my design at this time. 

8 hours ago, LegoDW said:

I was just about to suggest adding coloring to your water supply to aid in seeing the smoke effect, after watching your video see you have already thought of this.  Adding sound and steam effects into your build is a great effort and your results look fantastic.  Very well done!

Thanks!

Was it hard to get the speed of the Train Motors on the tender and the L-Motor in the engine to run at the same speed? I'm wanting to make my own version of 4449 with the auxiliary tender (Both tenders would have two train motors for additional pulling power) but wanted to get your insight on how you got the speeds to match up?

The  L-motor is geared 1:1 with the drivers so benefits from their larger diameter. In my experience, it's not necessary to worry about closely matching the speeds, the motor characteristics take care of it. It's not much different that IRL putting an SW1500 into a train of SD70's. They all contribute to the total tractive effort according to their abilities. I connect my motors in parallel to the Tsunami2 DDC controller so they all see the same voltage. As long as they aren't experiencing wheelslip, they will find an operating point on the torque-speed curve where they're happy. I'm not sure if it would be any different using a PF infrared receiver for power as that puts out a PWM voltage. This terrific resource shows how all the Lego motors produce more torque as they are slowed down when operating at a constant voltage: https://www.philohome.com/motors/motorcomp.htm This is similar to the series-wound DC motor characteristic of real locos.