Synchronised diesel smoke! First experiments

[RobjUK]

I mentioned in the DCC sound category a few weeks ago that I was planning to try an experiment to see if the output from a smoke generator could be made to pulse in time with a low-revving diesel loco engine.

 

Richard Croft's "dancing speaker" post of February 26th was a confirmation that a suitable bass speaker should be capable of moving enough air volume to modulate the smoke plume from a smoke generator.

 

 

It's taken some time for me to get the parts together & set up a suitable sound plus smoke config on a Loksound 5 XL with an ESU smoke generator, but I think it proves the concept - though it needs some tweaking and tuning to be fully practical for installation.

 

eg. I think a speaker with a low-pass filter would work better specifically for this purpose, so only the very low frequency of the engine firing rate is really passed to it strongly, rather than the whole audio spectrum. That would also allow some independent control between the air pulse intensity and the sound volume.

With the speaker in the test, too high a volume causes so much air displacement that smoke is emitted from the smoke unit fan.

 

 

Another reason for the coupler and T setup (which will hopefully be implemented in my build) is to route some sound output via the loco exhaust, both to add to the realism and put the speaker vent on the other side of the body metalwork from the speaker cone for better bass isolation. 

 

 

Two videos below. The first is a better view of the overall smoke output and although the pulsing is not extreme, I think it shows quite well that it is producing slight smoke pulses in time with the engine sound, and the occasional smoke ring can be seen coming away from the main smoke cloud.

 

The second one has the camera too close in and is not a particularly good view, but it shows an engine start part way through with definite pulses of smoke as the engine fires up (though the smoke then stops, probably due to my total lack of knowledge on how to properly configure a smoke unit...)

 

 

Test setup:

Loksound 5 XL loaded with ESU's Class 08 sound project, plus my first attempt to configure an ESU some generator, which is probably very wrong..

One of these speakers, coupled via  piece of brass tube fitted in the port & some bits of silicone tube: https://www.ebay.co.uk/itm/263597184299

Home made (3D printed) diaphragm coupler/isolator in line with the speaker port (to prevent smoke crud getting in to the speaker).

8MM plastic "T" piece, connected above the smoke gen and tube link from the diaphragm coupler to the branch.

 

I'll upload the coupler details and STL file in another post.

 

Note that this is purely a hypothetical "because it's there" experiment for me; the loco I'm actually working on would never have a pulsed exhaust.

However, I have the parts to hand & it will be some time before I'll need to finally install them, so experiments are possible at present!

 

Videos:

 

 

 

 

 

Edited April 14, 2019 by RobjUK
Added information

[RobjUK]

The coupler - photos (and .stl attached).

At 1:1 scale it's rather large, but it should be possible to scale to 75% or 50% and still work, with appropriately smaller screws.

 

The diaphragm is cut from the palm of a nitrile rubber glove and just sandwiched in place between two coupler halves, with just enough tension to get rid of most of the creases. At 1:1 scale, M2.5 screws are suitable and the connection OD is 8mm with 6mm bore.

The outside of the print is rather rough as I used a lot of support with it.

 

The yellow & black object in the last photo is just a screwdriver used to keep it upright for an edge-on photo, not any part of the thing.

 

Pulse3v4.stl

Edited April 14, 2019 by RobjUK
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