# chuff sensor



## bmwr71 (Jan 30, 2010)

Been thinking on my sound car project and understand that the mylocosound steam sound card sounds best with a chuff sensor. What would be the best way to add one of these to a car?

I did a car many years ago with some sound unit out of an HO car and somewhere I found someone selling a kit to add a chuff sensor to a car. But that was long ago.

Doug


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## Totalwrecker (Feb 26, 2009)

magnet and reed switch


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## TonyWalsham (Jan 2, 2008)

Make that 4 x magnets per loco driver revolution and a reed switch.
The MyLocosound Steam works very well with fast chuffs. There is still a distinct cut off even at fast speeds.


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## Dan Pierce (Jan 2, 2008)

For a caqr only one reed aqnd 1 magnet as the car wheels are much smaller than most loco wheels.
If a small loco like the LGB Chloe then 2 magnets.


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## Dwight Ennis (Jan 2, 2008)

Generally speaking, the whole purpose of a chuff sensor is to truly synchronize chuff with driver rotation... as was said, 4 chuffs per driver revolution for a conventional rod locomotive (and for nit pickers like myself on this, each chuff just after front or rear dead center of the pistons). That being the case, it makes little sense to me to mount the chuff sensor on a car wheel or anywhere else other than a locomotive driver. It should be easy enough to mount the sensor on a driver and run a couple of wires back to the follow car with the sound system in it using a micro connector between the two.


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## East Broad Top (Dec 29, 2007)

There are certain locos upon which wheel-mounted magnets would not work. For instance, LGB locomotives pick up power from the backside of the wheel via carbon brushes, so you couldn't mount the magnets so not to interfere with that. Even if you run battery power and can remove the brushes, the motor blocks often make it next to impossible to mount the magnets and reed switches. In those (and similar) cases, a tender-axle (or battery car mounted) magnet and reed switch set-up is the next best thing.

To get the correct number of magnets per rotation of the driver, you need to divide the diameter of the wheel upon which the magnets are mounted by the driver diameter to get the ratio of the two diameters. Then multiply that number by the desired number of chuffs per revolution (prototypically 4, though some who run particularly fast like only 2) to get the number of magnets you need per axle. For instance, if your driver diameter is 2" and the wheel with the magnets is 1", then 1 / 2 = .5, and .5 x 4 = 2. You would want 2 magnets on the axle to get the 4 chuffs per revolution. If your driver diameter is 1 3/4, and your tender wheel is 1 1/8, then you end up with 2.5 magnets per revolution, so you could use 2 and have slightly fewer than 4 chuffs per revolution, or go up to 3 magnets and have slightly more than 4 chuffs per revolution. For locomotives with really small drivers (Porter, plantation engines, etc) then you can go up to 4 magnets per axle on the battery car/tender. If you're doing a Shay or other geared locomotive, you may even find yourself looking at 5 or 6 magnets per wheel, as they had a chuff rate greater than 4 chuffs per revolution of the driven wheel. (The exact rate depended on the gearing and number of cylinders.) 

If you're doing a battery/sound car which will be used to power a variety of locomotives, then you'll probably want to look at the driver diameters of all the locomotives you'll be running and take an average. On my dad's railroad where most of his locomotives use tender-mounted triggers for the chuffs, we've found that 3 chuffs per axle gives the most pleasing results. (He's got one that's 2 magnets per axle, but the result is just too slow, so we're going to upgrade that one next summer.)

Later,

K


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## Jerry Barnes (Jan 2, 2008)

Mike Kidman told me about him mounting a chuff sensor inside the cylinder with a magnet and reed switch. One was mounted to the 'piston', one to the front of the cylinder. It was an Accucraft electric, so not sure about Aristo steamers.


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## Michael Glavin (Jan 2, 2009)

If I grasp the idea, Mike used the mechanically coupled movement and or position of one of the steam chests pistons to fire the chuff sequence. Intriguing idea... 

Michael


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## Treeman (Jan 6, 2008)

I did install a reed switch in the steam chest where the rod of the valve rod passed. With a rare earth magnet glued to the rod it triggered twice with each stroke, once going forward again going to the rear. I was using this switch to start and stop the fan in a MTH smoke generator. It would also work well for chuff.

https://www.facebook.com/ReindeerPass/videos/vb.417000258352021/792965677422142/?type=2&theater


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