# Chuff Sensors



## StanleyAmes (Jan 3, 2008)

I am rebuilding an Accucraft C-16 and wish to install a chuff sensor on a driver to get correct 4 chuffs per revolution.

I asume that magnets triggering a reed switch is the perfered approach.

What are experiences people have with magnets on the axle or on the driver.

If on the driver what size magnets are people using, where do you get them, and how are you gluing them onto the rear of the driver.

Is there anothe solution that has better response time then a reed switch and could be installed on the C-16?

Thanks

Stan Ames


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## K27_463 (Jan 2, 2008)

Stan, the clearance and space available on the Accu c16 is very tight. you could glue them to the back side perimeter of the driver with super glue, this will work but is risky as they are likely to get knocked off because they mist be paced near to the extreme edge, and everything is too close. 
Best solution is to go to hardware store, purchase a large stiff rubber plumbing washer, home depot and lowes have them, with center hole very close to the c16 axle size. Slit it and slip it over the axle , then use super glue to seal the cut. Then place 4 magnets on the perimeter of the washer and mount your sensor. Super glues bonds rubber very well, and bonds magnets to rubber well also. Since the rubber is flexible, if loco derails, hits debris or fouls a set of points, nothing breaks or fails. 
Do this on the 4th axle , and while you are there mount an orange or red LEd down there inside the firebox bottom for some ashpan glow 

Jonathan/EMW 
www.rctrains.com


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## Del Tapparo (Jan 4, 2008)

Stan - I use rare earth magnets from Radio Shack. Click Here.
I glue them to the tender wheels or trailing car wheels with super glue for two chuffs per revolution (works for me). I've never had any problems with the response time of a reed switch.


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## Greg Elmassian (Jan 3, 2008)

Some people have milled/drilled recesses in the back of the loco driver, and used small, thin super magnets with success. This way there are no clearance issues. 

Greg


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## Dwight Ennis (Jan 2, 2008)

SoundTraxx used to sell a "chuff cam" kit for smaller scales. It consists of a PC board with several different cams printed on it in various sizes... some 4 contacts per revolution, and some 8 or even 12 (if memory serves) for geared locos. It also comes with a phospher bronze wire to be used im making the contact. Not sure if they still make them.










While made for the smaller scales, I have used them and I know they could be easily adapted for your purpose.


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## K27_463 (Jan 2, 2008)

Accucraft drivers have insulation between the cast brass spoke center and the stainless tire. For this reason it is not advisable to machine a recess, the avilable area is again very limited and would require drilling across the insulationwhich could short it, and removal of the driver from the frame and consequential requartering. The magnet thicknes is not really an issue, the standard Phoenix magnets are fine. The problem is tight clearance and the way the frame is set up in relation to the rear driver of the loco. If magnets are mounted on teh back of the driver, then snesor mounting position becomes problematical. Of course tender wheel mounting will work, but if you want prototypical synchronized 4 chuffs, then driver mount it is, and the scale tire thickness cross section simply make s it easy to knock a magnet off in operation, which then results in a sick sounding chuff. 
To each his own. 
jonathan/EMw 
www.rctrains.com


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## TonyWalsham (Jan 2, 2008)

Here is how I did the chuff sensor on a K-36.

I know it has more room than the C-16 but given the tiny size of the magnets there should be enough.

First I made a paper disc to accurately locate the magnets relative to the reed switch which was mounted end on to the Rare Earth magnets. End on gives more precise switching.










When the super glues was completely hard the paper disc was removed. I later painted the reed switch and mount etc matt black.


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## Greg Elmassian (Jan 3, 2008)

I think chuff "cams" can still be had by Grizzly Mountain Engineering. 

greg


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## StanleyAmes (Jan 3, 2008)

Thanks for all the input. I liked Tony's suggestion the best but quickly found out that Jonathan had first hand experience on this locomotive. Unless I want to remove the track pickups an axle mounting is the only way to go. I am a little concerned about the release time of the sensor but will give it a try and post the results. 

Thanks 

Stan


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## TonyWalsham (Jan 2, 2008)

My apologies. 
I neglected to mention that mounting of the magnets was for battery only. 
Nevertheless, using a paper disc to accurately align the chuff signal with the piston stroke, is desirable.


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## Dwight Ennis (Jan 2, 2008)

I looked at thew Grizzly Mountain Eng cams Greg. They don't specify an axle size, but my bet is it's for smaller (HO,N) locos. Might be worth an email though.


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## nkelsey (Jan 4, 2008)

Hey Stanley, while we are talking chuff sensors, any hints on how to make the Mallet cheuff sensors play nice with QSI?


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## Cougar Rock Rail (Jan 2, 2008)

Stanley, I have a couple of suggestions: 

Have a look at the kit that Massoth sells--it's based on a hall-effect sensor and comes with an axle, sintered magnet wheel and sensor. You can use your own axle, drill out the magnet wheel to suit as well, which I what I did on one of my locos, and that worked very well. 

I also made a magnet wheel by machining a round plastic disc to press on the axle, then drilled four holes in it and pressed in small magnets, and used a reed switch that stuck into the motor block from above. You just have to be mindful of the fact that axles need to be able to float so however you do it allow for that when you put in the sensor. 

Keith


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## gnichols (Jan 9, 2008)

I've had no problem super-gluing magnets to the inside of Accucraft loco drivers, but you may have to add a thin sheet of plastic to gap spokes if your magnets happen to fall in the wrong place. I normally mount a Phoenix type reed switch on a sheet of ABS or thick styrene to the chassis some place convenient between on set of drivers using existing screws if I can, by drilling and tapping holes, or with ty-wraps. I mount the reed switch on the ABS by drilling holes for two ty-wraps to hold it on. That way, you can "adjust" the switch and replace it easily without taking the loco apart. It isn't pretty, but it works. You may have to mount the reed switch diagonally to get it to fit between the drivers, but no worries. You can also mount it vertically using the same technique but will probably have to epoxy or glue gun it in place. Before I glue on the magnets, I adjust the crossheads so one of the pistons is at full extension. The loco should chuff when this piston is either all the way back or all the way forward. Either side makes no difference, if your loco is properly quartered, the sound will be just fine. Then plan where the magnets will go. If it looks too hard (one magnet will have to be glued in the "air" between two spokes, you might have to rotate things a few timesthin until it looks better. If not, add some plactic to fill the gap. Glue the magnets on as close to outside of the wheel as you can and be sure to get them as close to 90 degrees apart as you can, or your loco will limp a little. Again, take your time to size up the situation and glue them on one at a time carefully. Debonder will take them off should they slip out of place. Gluing them on the axle will work, but is very hard to get them exactly 90 degrees apart. I use the small magnets from Radio Shack, which are the same size as the Phoenix ones. Hope this helps, Gary


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## Lake Valley #1 (Dec 31, 2012)

Back in the days before I knew about magnets and reed switches, I rigged up a 4 chuff system using a square nut and a mini microswitch. I put it in a B-mann Big Hauler on the front axle (because it was the one with the most room). To do it, I drilled out the nut to the axle diameter, then cut the nut in half and JB welded it back together to the axle, checking to make sure it would chuff at the end of the piston stroke; in other words, the points of the nut would close the micro switch at the proper time. Then I built a bracket to mount the micro switch to, wired it up, adjusted the 'wiper' arm on the micro switch to get the best chuff at medium speed. I'll probably do it again since it worked out quite well. The nut size was for a 10-32 machine screw. If memory serves the nut was about 5/16ths on each side, so drill carefully.


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## East Broad Top (Dec 29, 2007)

So far as "release time" goes with magnetic sensors, I'm almost exclusively magnets/reed switches on my chuff triggers. On two of my probably 12+ installations, I have an issue where in one direction the magnet trips the reed switch very evenly through the rotation, but when going the opposite direction, it's ever-so-slightly uneven. Got to be something with the magnetic field, but since it's ever-so-slight, and only in reverse, I don't worry too much about it. And Stan, if it's a touch uneven, consider it to be slightly out of square.  (Note to readers--inside joke...) 

As for the C-16, I'd be tempted to consider mounting the switches on the tender wheels. Compare the diameters of the two. I know on the Bachmann C-19, the ratio between the diameters of the drivers and tender wheels are almost exactly 4:3. So you can mount the magnets at 120-degrees on the tender wheel and never know they're not triggering off of the drivers. If memory serves, the C-16s had the same size drivers as the C-19s (37"), though I'm not certain the tender wheels would be the same diameter, nor do I know if on the model they'd have such a convenient size ratio. 

I use 1/8" diameter, 1/16" thick rare-earth magnets I bought online. I forget where, but I got something like 100 for $8 or something ridiculous. If I were to re-order them, I'd go with the 3/16" diameter ones. A little stronger magnetic field, so the placement of the reed switch isn't quite as critical to the installation. With the 1/8" diameter ones, I've got to make sure there's very little lateral play in the axle so it can't move away from the reed switch. 

Later, 

K


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## Greg Elmassian (Jan 3, 2008)

good place to get the magnets is on ebay, many sold there for good prices and many sizes available. 

just search "rare earth magnets" on ebay, lots of choices. 

Greg


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## VictorSpear (Oct 19, 2011)

For harsh, noisy environments I use a latching hall effect IC from Melexis (US1881). 

Has a small and neat form factor, very low supply current (5 mA) , wide op voltage range (3.5-24V), 0.25 mu sec rise/fall time.
Built-in voltage regulator, chopper-stabilized dynamic offset cancellation, Schmitt trigger in one tiny package.










Rear mounted magnets in hollowed out wheel









Or, front mounted

Cheers, 
Victor


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## Greg Elmassian (Jan 3, 2008)

Victor, I'm a bit confused by the documentation, or not seeing your pictures well. 

This latching means that you have to pass a south pole by to latch it on (open collector low), then pass a north pole by to return it to high impedance state. 

Many people use a small button magnet, with only one pole facing the sensor, but for this device, you need a small "bar" type magnet, to pass both poles by the sensor. 

Is this a correct understanding? 

Greg


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## VictorSpear (Oct 19, 2011)

Absolutely correct Greg. One micro-magnet has the N pole affixed symmetrically opposite to the S pole of the other. The guaranteed hard latch is then in effect and substantially reduces the offset width and stray hysteresis found in single magnetic solutions. Precision is superb from 0 to 9000 rpm in metallic surroundings close to the motor armature.


Victor.


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## Greg Elmassian (Jan 3, 2008)

Thanks Victor, do you have a closer picture of the magnets you used, or the dimensions? (or where to get them) 

Thanks! 

greg


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## VictorSpear (Oct 19, 2011)

Sure...



















Available at http://www.digikey.com/product-search/en?mpart=US1881LUA-AAA-000-BU

And magnets at:https://www.sparkfun.com/products/8643


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## VictorSpear (Oct 19, 2011)

Forgot to add the link for the 0.125" magnet shown in the pictures : https://www.sparkfun.com/products/8644


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## Greg Elmassian (Jan 3, 2008)

Thanks Victor, will have to try it out. 

Have been working on a page for chuff triggering methods: http://www.elmassian.com/trains/dcc-battery-rc-electronics/sound-systems/chuff-triggers-and-wiring 

Regards, Greg


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## East Broad Top (Dec 29, 2007)

Victor, if it's a latching switch, are you only getting one chuff per revolution, then? 

Later, 

K


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## Greg Elmassian (Jan 3, 2008)

No, one trigger "pulse" per magnet. 

The magnets he is using have both north and south poles "picked up" by the sensor. 

so each "passing" will generate a chuff pulse.... yes he has 2 chuffs per revolution as I understand it. 

You might want to re-read my question about this and Victor's answer... or my link to my site I provided









Greg


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## East Broad Top (Dec 29, 2007)

Thanks for clarifying. 

K


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## VictorSpear (Oct 19, 2011)

Greg is right again. With just 2 opposing magnets, we latch on, latch off in one revolution, yielding 2 pulses. 


For sound processor instructions, we extrapolate from the bipolar 2 magnet data - we compute the time in milliseconds for one latch on/latch off (half a rev) , then trigger the sound processor to raise 'n' chuffs based on the computed full revolution timing (a settable parameter..like for steam, n=4). We then wait for any change (*the* *delta*) in latch on/off timing duration to send in the next adjusted computed timing instruction cycle to the sound processor. The objective is to achieve a smoother variant in sound ramping, with a reduced staccato gunning effect at higher speeds. 


Cheers,
Victor


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## East Broad Top (Dec 29, 2007)

Okay, now I'm confused again... 

Each magnet has a north and south pole, so each magnet is opening _and_ closing the sensor (i.e, open/close ---- rotate 180 degrees ---- open/close ----rotate 180 degrees), or does one magnet open the sensor, then the other one close it (i.e., open ---- roate 180 degrees ----- close ---- rotate 180 degrees) If the latter, then you're using the change of state to trigger the sounds to give you two pulses per revolution as opposed to just triggering the chuff when it's closed? 

Later, 

K


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## Greg Elmassian (Jan 3, 2008)

Victor, with the speed capability of the sensor, have you tried to double the magnets and get 4 per revolution? 

I think most systems cannot extrapolate, they can divide down but not extrapolate up. 

Thanks, Greg 

p.s. I'm probably going to buy a few and see how I can have them work, and maybe gen up a little circuit on my site, but of course the example circuits on the spec sheet are completely adequate. I like the fact that it should be able to connect to existing sound cards with minimal components.


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## Garratt (Sep 15, 2012)

Posted By Greg Elmassian on 01 Jun 2013 07:10 PM 
No, one trigger "pulse" per magnet. 

The magnets he is using have both north and south poles "picked up" by the sensor. 

so each "passing" will generate a chuff pulse.... yes he has 2 chuffs per revolution as I understand it. 

You might want to re-read my question about this and Victor's answer... or my link to my site I provided









Greg 
Greg, this apparently is the problem with USA Trains dockside. It has too many chuffs which is produced by both poles of the magnet. A fix was to put some metal near the sensor to lower the sensitivity.

Andrew


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## VictorSpear (Oct 19, 2011)

Kevin, Change of State triggers the pulse...right on - one magnet opens drain, the other closes. If it was N+S presented for each magnet, there would be too much noise (jitter). You want a hard open - hard close with precision. Greg, yes an additional pair of magnets at 90 degrees will give the mechanical 4 chuffs per revolution. This works fine for steamers. 

However we want to be cool so we try to do it with less  Also I borrowed the stainless steel wheels from a colleague who didn't appreciate me drilling holes in his precious wheels so we settled for 2 magnets and used more Math instead. 


Cheers
Victor


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## East Broad Top (Dec 29, 2007)

Thanks! Now all is clear. I might have to do some playing around myself. I've got a few locos with flaky reed switches; this sounds like it might be a bit more predictable. 

Later, 

K


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## Greg Elmassian (Jan 3, 2008)

Yeah, drilling hole in SS is not my idea of fun either! 

Looks like an Aristo block, with the short-lived run of SS wheels... 

Regards, Greg


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## Paul Burch (Jan 2, 2008)

Here is another source for magnets. 
http://www.kjmagnetics.com/Default.asp 


http://www.kjmagnetics.com/products.asp?cat=10


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## Greg Elmassian (Jan 3, 2008)

Thanks Paul, I've put that link on my page! 

Greg


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## Cougar Rock Rail (Jan 2, 2008)

I find it funny you guys are reinventing the wheel. LGB/Massoth has been using these hall effect sensors and magnets for years (as I pointed out two years ago above)...I'm beginning to wonder if people actually read what others post or just bull ahead with their own thoughts? 

Keith


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## Greg Elmassian (Jan 3, 2008)

Uhh.. speaking of reading, did you read my page? It properly credits with LGB using this first. The link is above. (5:15 pm June1)

But, this is an added wrinkle with latching units, and a different magnet configuration. This is the difference.

I've encountered problems with ordinary hall effect sensors where they can double trigger (USAT Docksider) and this was caused (I think) by interference in the magnetic field, causing false triggering. This latching methodology might solve my problem.


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## VictorSpear (Oct 19, 2011)

That KJMagnetics site from the link posted does a good job with great prices including describing the direction of magnetism needed for this method. For this exercise, be sure to order '*axially magnetized*' for cylindrical or '*magnetized through thickness'* for cubes.

http://www.kjmagnetics.com/magdir.asp ...excellent 


(Note: If using the 1/8" cube, simply let the 2 cubes naturally mate. Then separate at the mated joint where N/S have mated, mark them with colors and place them 180 deg apart, or 90 deg apart as needed. You really don't care which is N or S as long as opposite faces are presented).


Keith, ....Ummm..the Hall Effect was discovered by Edwin Hall in *1879*.... Hall Effect Applications are still evolving including Cardiac Imaging recently replacing reeds switches found in pacemakers .. 
http://www.medscape.com/viewarticle/749751_3


Cheers
Victor


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## Cougar Rock Rail (Jan 2, 2008)

Uhh.. speaking of reading, did you read my page? 

Of course not!  

If you look at the way LGB/Massoth do the triggering, they use a sintered material that somehow encapsulates the magnets--it's a good way to do it inside a gearbox because then if there is lateral play it won't knock the magnets off etc. I also suspect they can mount them in the correct orientation to minimize the stray field. I would suggest you try one on your docksider and see if that helps, and makes the latching version unnecessary.


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## Greg Elmassian (Jan 3, 2008)

Keith: I don't think it is a "stray field" but interference in the field by other stuff moving near by that may make a "double hit". If you did not read my page then I guess you did not watch the video ha ha! 

Anyway, you seem to insist on not "getting" the advantage of a two state system, that it intrinsically would eliminate on what I THINK is happening. 

On normal hall effect sensors, you just want a field of any polarity to sweep by, consistently. I think it's the other stuff moving that causes the problem, as evidenced by the "damping" I applied and going back to single chuffs. 

Victor, what do you think? 

Greg


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## VictorSpear (Oct 19, 2011)

In close metallic surroundings around motors and magneto-sensitve material, the magnetic eddy is large - adding to the noise and false debouncing from hysteresis you can experience when the magnets are close to each other like a gearbox. I'd like to try that Massoth sensor at 500...1000....9000 rpm some day. Can it be had for under $ 5 in total including sensor, magnets and postage  ? Haven't found anything from LGB under $ 25 though.


Cheers,
Victor


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## Cougar Rock Rail (Jan 2, 2008)

Ha ha!, no I did watch the video. I understand the advantage of the latching method--it's definitely better I'm just saying it shouldn't be necessary as there are examples of it in this application where no problems exist. I noticed on your video you were only getting two chuffs per rev not four--is that the way they designed it? I still think if you used the sintered Massoth magnet wheel your existing hall-effect sensor would work fine. 

Keith


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## Greg Elmassian (Jan 3, 2008)

Yes, designed as 2 chuffs per... typical compromise between slow speed and high speed "machine gunning". 

I'll have to look into solutions, and investigate how the magnets on the Docksider are oriented. 

I'm interested in a method that is simple with all the brains in the chip too. 

Greg


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## Cougar Rock Rail (Jan 2, 2008)

Greg, here's the way I did it in my Heidi where I used magnets/reed. Later when I changed decoders I went to the hall-effect sensor but this method of holding the magnets worked well and was pretty easy to make:


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