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Author Topic: Sound Cam in Mallet 2-6-6-2T?  (Read 2265 times)
Peter O

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« on: April 26, 2011, 01:25:46 PM »

I have the QSI Magnum installed in my Mallet, but wondered if anyone had changed the simple install from a pnp with synchronized chuff, to using the chuff cam that I understand this engine has. I'm reasonable satisfied with the chuff effect as is, but would be interested to know if the results are better using the mechanical method and presumably, a compound setting to get the in/out of sync effect.

Peter.
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Kevin Strong


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« Reply #1 on: April 27, 2011, 01:28:46 AM »

I'm not sure quite what you're asking. The "synchronized" chuff on the QSI would be one that reads the signals coming from the optical sensors in the cylinders, which would be quartered with the drivers. The alternative would be the "auto chuff" which nominally reads the speed of the motor and sets the rate of chuff based on the rotation of the motor. The QSI's auto chuff is okay, but it doesn't have the ability to remain perfectly synced to the rotation of the drivers throughout the entire speed range. You can usually get it "close enough," but if you've got the triggers, why not use them?

The optical trigger inputs can be found on the main circuit board. I think that's the J1-5 (marked "chuff") and J1-7 (ground) pins. With the QSI, you have to physically connect the chuff triggers on the QSI board (Plug 2, pins 1 and 2) to the optical chuff triggers on the loco. The plug-in pin at J1-5 doesn't connect to anything on the QSI board. You'll have to do a bit of tracing to find out where you can tap into that pin, but an ohm meter should help you there. If I'm reading the circuit diagrams correctly, you'll connect J1-5 to P2-2 on the QSI and J1-7 to P2-1 on the QSI (then set the appropriate CV on the QSI to go by triggers as opposed to auto chuff. I don't remember which CV that is, and I'm too lazy to go looking for my QSI manual at the moment. It's in there, though.) I've not connected a QSI in the mallet, so I can't say 100% that's what's going to work for you. I'm just going by the Bachmann and QSI circuit diagrams. Hopefully someone else will chime in with practical experience.

Now, as for the articulated "in/out of sync" effect, know that the Bachmann mallet is a compound mallet, so you'd only hear four exhaust beats per revolution, timed to the forward cylinders. A compound mallet feeds the exhausted steam from the rear set of cylinders (called "high pressure" cylinders) to the forward set (called "low pressure" cylinders.) The exhaust from the forward set is sent to the stack. That's why the forward cylinders in a compound locomotive are so much larger than the rear set; the steam is at a lower pressure, so the cylinders need a proportionally larger surface area for the lower pressure steam to act upon. Of course, it's your loco and if you want to play with the in/out of sync sounds, more power to you.

Later,

K
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StanAmes


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« Reply #2 on: April 27, 2011, 07:30:21 AM »

As Kevin has pointed out at speed a compond mallet will only have 4 chuffs per revolution.  However many compond mallets have a lever so that the engineer can switch the locomotive into simple mode at low speed for extra tractive effort.

On my mallets, I have a function that when ON both sensors are active and you have the slow speed sound effect of "in/out of sync"  As you speed up you, turn the function OFF and the locomotive acts like a compond mallet.

Hope that helps.

Stan Ames
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Peter O

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« Reply #3 on: April 28, 2011, 10:48:28 AM »

Thanks for the replies. Sorry if my terminology was confusing.

My understanding is that by simply removing the dummy plug and installing the Quantum Magnum, that the only option I have is "auto chuff" since there is no standard defined on the 12(?) pin board connector (Aristo/Bachmann psuedo standard) for the sound trigger. Right?

There's a seperate two pin connector on the Magnum which a sound trigger can be connected to and somewhere on the Mallet board is a connection to which one could join it. Right?

So then the next questions are; does the Mallet use the later optical trigger mechanism and do I need to dig up the info that was developed for the K-27 to build a small circuit between the Mallet and the Magnum to make it work?

Final question, is it worth this aggravation or should I just continue to experiment with the auto-chuff settings to get it close to perfect?

Again, thanks for the help so far. peter
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Kevin Strong


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« Reply #4 on: April 28, 2011, 11:28:12 AM »

My understanding is that by simply removing the dummy plug and installing the Quantum Magnum, that the only option I have is "auto chuff" since there is no standard defined on the 12(?) pin board connector (Aristo/Bachmann psuedo standard) for the sound trigger. Right?

There's a seperate two pin connector on the Magnum which a sound trigger can be connected to and somewhere on the Mallet board is a connection to which one could join it. Right?

That's correct. As a straight plug-and-play system, you'll have to use the "auto chuff" feature. Connect the wires that go into the chuff trigger plug on the QSI to pins J1-5 and J1-7, set the appropriate CV on the QSI to triggered chuffs, and you "should" be good to go. (I remind you that this is theoretical, not firsthand knowledge that it does work.)

Quote
So then the next questions are; does the Mallet use the later optical trigger mechanism and do I need to dig up the info that was developed for the K-27 to build a small circuit between the Mallet and the Magnum to make it work?

No. My understanding is that the electronics were "corrected" in the mallet so that you do not need any additional circuitry. I'm told they're the same as what's in the Climax, and the Climax triggers worked well with a Sierra board when I was experimenting by connecting J1-5 and J1-7 to the chuff trigger inputs.

Quote
Final question, is it worth this aggravation or should I just continue to experiment with the auto-chuff settings to get it close to perfect?
Realistically, if all you're after is the sound of exhaust and don't spend time watching the drivers to know that it's not timed to quarter, then the "auto" will be close enough. Me? It's well worth it to engage the sound cam. I've done a few locos with the "auto chuff" feature, and my experience is a mixed bag. One loco was perfect throughout the speed range once I got it set, and very consistent day to day. I've got another that I can't get timed properly for love or money, and it "slips" from day to day. Different locos, different motor (though both Pittman motors), so your mileage may (and likely will) vary. But I've got "calibrated eyeballs" in that regard, and can tell fairly quickly when the exhaust doesn't match the quarter. And yes, it bugs me to no end, so I use sound cams whenever possible. (Alas, I built my "problem child" loco with the intention of using auto chuff based on my good experience with the first loco. I'll switch it to a sound cam the next time it goes in for service. Problem is, it's a Barry's Big Trains chassis, so that may be a while...)

Later,

K
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Peter O

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« Reply #5 on: May 04, 2011, 11:42:17 AM »

Kevin, great info as usual.

I will make the change to use the chuff cam and let everyone on the board know how it goes.

Thanks.

Peter.
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