Chuff Rate Question

[MarkInLA]

Hi, sorry if this is a worn out subject. And I can't find the topic from an earlier date. so I will go ahead and repeat topic..: Is it correct to conclude that matching the chuff rate so that 4 chuffs occur for every complete turn of the driver on a Bachmann HO mogul using an NCE Power Cab throttle while programming on the main after entering CV 116 and after we choose a value for 116, 'enter' MUST be clicked in order to see the results of that value ? If so, synching cuffs to wheels is so tedious..I hear one should give CV 116 about 1/2 its value ( 255 Div. by 2 is about 127) and enter this whilst loco is warmed up an rolling. I have done this but still must continually go back to screen , enter CV 116 then enter another value by trial and error and hit 'enter' over and over to try synching chuffs..Is it possible to remain in CV 116 and just raise and lower values until we see the chuffs matched up , and THEN hit 'enter' to lock in that value ? Also , is there a setting which remains perfectly in sync ? Or does it eventually go out of sync on EVERY  steam loco ?     Thanks, Mark

[Tom M.]

Mark,

Yes, you are stuck with the trial and error method unless you use DecoderPro and have if interfaced with your layout.

The only way to get the chuff rate in perfect synch with the wheel revolutions throughout the entire speed range is to install either a mechanical cam or an optical cam.  Grizzly Mountain Engineering offers mechanical axle cam kits.  SoundTraxx offers mechanical cams that mount to the back side of a drive wheel.

If you don't use a cam system, the best you can hope for is an approximate timing.  You will need to make a decision about how you plan to run the loco.  For example, will it run most of the time in low speed service or will it be run in high speed service.  Once that is determined, you will want to set the chuff rate to best match it.  For the most part, my locos run in low speed freight service, so I set the chuff rate to best match that.

Regards,

Tom

[rbryce1]

OK, really hate to ask this one, as it may show my ignorance, but why would there be 4 chuff's per wheel rotation.  

Seems to me one chuff would come from moving the drive piston one full stroke which would turn the wheel 180 degrees, and the second from the drive piston moving in the opposite direction a full stroke, turning the drive wheel the other 180 degrees.

If there were 4 chuff's per rotation, the first stroke would only turn the drive wheel 90 degrees and the second would just pull the drive wheel back to where it was before.

I could maybe follow it if there were two "double Chuff's" in rapid succession, on for each piston on the opposite sides of the engine, but would a "doule Chuff" sound that much like two seperate chuffs?

Think I really need help on this one.  

[jonathan]

The right and left side driver wheels are positioned 90 degrees off from each other.

So... two chuffs per rotation on the right side, two chuffs per rotation on the left, occuring 90 degrees off from each other. Hence, you hear 4 chuffs per rotation.

Hope I wrote that right.  We're all learning together, so don't feel bad. 

Regards,

Jonathan

[rbryce1]

Still don't follow that.  One chuff MUST seem like it has to turn the wheel 180 degrees and the second to return the other 180 degrees.  Two 180 dgress movements would be the 360 degree circle.  If they were only turning 90 degrees, each one would osculate back and forth over a 90 degree range and get nowhere.

[Thomas1911]

Maybe 4 chuffs per AXLE revolution is a better term.  What Jonathan is saying is the right and left drive wheels on each axle are indexed 90 degrees out of phase, hence the term "driver quartering".

When the right cylinder is at the ends of its stroke, the left cylinder is mid-stroke.  Each cylinder is still "firing" (not sure what the actual steam term is) at 180 degrees per wheel revolution, but the left and right cylinders are "firing" 90 degrees apart.  This results in you hearing 4 chuffs per wheel revolution when looking at a locomotive from one side.

[Joe Satnik]

Dear rbryce1,

Try this:

Each piston pushing ...

Each piston pulling ..

Left rearward ..
Right rearward ..
Left forward ..
Right forward ..

SEE BETTER EXPLANATION IN POST BELOW

repeat....

I may have the right/left (handedness?) mixed up....or both may have been made throughout loco history..

K probably knows which one is more predominant.  

Hope this helps.

Sincerely,

Joe Satnik

Edit: point to better post below

[rbryce1]

I can follow that as two chuffs per side, 180 degrees apart, but you would only hear two large chuffs at the same time , one large chuff from both sides forward and one large chuff from both sides in reverse, correct?

[Thomas1911]

I tried to find an animation, but didn't have any luck.  Maybe this will help.

http://home.roadrunner.com/~trumpetb/loco/cbal.html

Notice how the position of the crank pins on the wheels, how they are clocked from sided to side.  They are 90 degrees apart.  If they were 180 degrees apart, you would hear only two chuffs.

[Thomas1911]

rbryce,
I drew this up in CAD maybe this will help also.  Imagine the green siderods to be near-side, purple would be far-side.  You can see how the green rods trail the purple rods by 1/4 (90 deg) wheel revolution.  Guess I drew them running in reverse.

[rbryce1]

Thomas1911,

Your drawing does, in fact, show that a 90 degree movement will not work, as the first two movements of the piston will rotate the wheel 180 degrees and the second two will return it back to where it was, not progressing forward.   I did notice, however,  the same site you reference does have the animation for both forward and reverse animation, and they DO in fact, show 180 degree wheel rotation for each stroke of the piston!

http://home.roadrunner.com/~trumpetb/loco/cbal.html


If you go to the site and scroll to the bottom of the page and select "Forward Animation", you see the wheel turning 180 degrees for each stroke of the piston in each direction.

HOWEVER, if you turn on the sound and closely observe the chuffs (4 of them per wheel rotation) watching not the operation of the piston and wheel, but the operation of the slide valve, the:

first chuff is admitting steam to push the piston forward.
second chuff is exhausting steam as the piston goes forward
third chuff is admitting steam to push the piston backwards
fourth chuff is exhausting steam as the piston moves backward.

The turning of the wheels is in sync with the first and third chuff AND it goes in line with the difference in volume between the first and third chuff and the second and fourth chuff, as one is exhausting to atmosphere (louder) while the other is pressurizing the cylinder (more muffled).

Watch it and see if you agree!

The way I am interpreting the animation:

When an engine is at rest, there is no steam on either side of the piston.

Once steam is admitted to the right side of the piston, it starts moving to the left.  The slide valve moves and allows the air on the left side of the piston to be exhausted, causing no noise because there is no steam on the back side of the piston yet and resulting in a single chuff.

Next, steam is admitted to the left side of the piston, causing it to move to the right.  The slide valve then exhausts live steam from the first movement, resulting in 2 chuffs, a pressurizing chuff followed immediately by an exhausting chuff.

From then on, there are two chuffs for each movement of the piston.

When the engine stops, the trapped steam in the cylinder must be vented, which results is a large whooshing sound instead of a chuff.

[NWsteam]

http://youtu.be/3Tiee5k7aXY?t=1m54s

Start at 1:54

HOWEVER, if you turn on the sound and closely observe the chuffs

The chuff is a gimmick and not in time with the animation. I watched with the sound on and after 2 rotations the sound wasn't even close to right.

-Brad

[Joe Satnik]

Dear All,

Brad's video clearly shows 4 chuffs per revolution.

Try this again:

I don't know if the live unused steam causes any sound entering the cylinder, (hissing?)

but I know that at the same time, exhaust (used steam) is pushed out of the opposite end of the cylinder,

and piped up and out of the stack with a "whoosh" sound.

Mod of my previous post:

Live unused steam enters the front of a cylinder, pushing its piston toward the rear of the cylinder (push power stroke), which forces exhaust steam out of the rear of the cylinder and up the stack, producing a "whoosh" sound. 

Live unused steam enters the back of a cylinder, pushing its piston toward the front of the cylinder (pull power stroke), which forces exhaust steam out of the front of the cylinder and up the stack, producing a "whoosh" sound. 

Left piston rearward (whoosh from rear of left cylinder)
Right piston rearward (whoosh from rear of right cylinder)
Left piston forward (whoosh from front of left cylinder)
Right piston forward (whoosh from front of right cylinder)

repeat...

Hope this is less confusing.

Sincerely,

Joe Satnik

[rbryce1]

Joe,


Your explanation seems very good as well.  No matter which is correct, I understand better how there can be 4 chuffs instead of 2.

[bmjcook]

OK, really hate to ask this one, as it may show my ignorance, but why would there be 4 chuff's per wheel rotation.  

Seems to me one chuff would come from moving the drive piston one full stroke which would turn the wheel 180 degrees, and the second from the drive piston moving in the opposite direction a full stroke, turning the drive wheel the other 180 degrees.

If there were 4 chuff's per rotation, the first stroke would only turn the drive wheel 90 degrees and the second would just pull the drive wheel back to where it was before.

I could maybe follow it if there were two "double Chuff's" in rapid succession, on for each piston on the opposite sides of the engine, but would a "doule Chuff" sound that much like two seperate chuffs?

Think I really need help on this one.  

Gidday
            Now for the second lesson! Why do three cylinder locos have 6 chuffs per wheel rotation? How many chuffs per wheel rotation do 4 cylinder locos have? Three and four cylinder locos are common in Europe........Cookie