Posted By rbednarik on 12/20/2008 9:56 AM
One more thing that can affect the chuffs you hear is whether the valve gear is in Full ("in the corner") or backed off to nearer the "Company notch". When the valve gear is backed off this way it is possible for the "D" to not move far enough to actually admit steam into the cylinder and that will produce fewer chuffs per revolution. On my Mikes, I can get it down to just one chuff per revolution... i.e.: the loco is actually running on just one end of one cylinder, which at very slow speeds can produce a very jerky motion to the train... I have had the tender connection slip loose such that the train is being towed by the rubbery hoses instead of the drawbar and when running slow on one end of one cylinder the train can look like an "inchworm" or some animated cartoon "choo-choo".
That is a good reason for not hearing all 4 in a strong staccato beat, but in this case it is also related to the quality of the sound found on youtube. Try listening to it in a high resolution mode, which is stereo sound compared to the normal split channel mono sound waves.
Company notch should not cause one beat per revolution, and by running the engines like this, you are causing adverse wear and tear on the valve gear. The same applies for full-size locomotives, all of them have a cutoff ratio, normally around 75% from neutral. The mikados have three notches in either direction of travel. When running, only the second two (from neutral) should be used on a properly timed locomotive. The notch closest to neutral is useless since it is past the acceptable amount of reduced travel the valvegear can support. As you said, notch one (from neutral) causes a severe jerking motion, just imagine the stresses produced on the valvetrain!
Mark, once the locomotives start to accelerate, they are usually notched up, which retards the valve timing so that the pistons have a cushion of steam at higher speed. You are having trouble distinguishing the beats at a higher rate of speed, once the staccato reaches a point where the strongest side of the locomotive (yes they are power biased, even the best running engine will have a stronger side) your ear can only detect the stronger beats. It is also related to stack geometry and how much velocity of steam is allowed through at a time.
I have disconnected the notched quadrant in the cab of my Mikes and am using a servo mounted under the smokebox to control the valve cutoff. Thus I can get mine to infinite settings, including much closer to "zero" than others can do. As long as I am running FAST I only notice that the chuffing is slower than it should be, (but it is still pretty much of just a quiet roar).
I regularly run with the valves set to such a cutoff as to run on just one end of one cylinder and I think that would be equivalent to about notch 0.2 on the quadrant in the cab! I get considerable longer run times (well, much less water usage for the given fuel fill) that way.
For slow running, I start in full gear (in the corner) and control speed with the throttle, but once it is moving, I have to back off on the valve gear to keep the speed down, but then I lose the nice Chuffing it is capable of. Takes a heavy train to get good sound and keep the speed slow. I need to alter my R/C transmitter controls to add some ratcheting or notches to hold them in place as it is very hard to keep them at just ONE setting with just my thumb on the reverser (wheel) and index finger on the throttle (trigger). I eventually want to build my R/C car controller into a mockup of a cab with a full sized reverser lever with a notched quadrant and a throttle bar on a faux boiler backhead (and maybe a remote TV camera in the locomotive and a TV screen in the front window of the cab mock up).