Here’s the situation: Soundtraxx decoders; CV # 54 contains a value n between 0 and 255 that determines chuff synch rate as a proportion of throttle for ‘Auto-Exhaust’ operation. This is used if there is no cam on the drivers to trigger the sound. The formula Soundtraxx provides is CV value = 115.9 X SPD/DIA where SPD is loco speed in scale MPH at Max throttle and DIA is driver diameter in scale inches. I have found this to be less than satisfying for a number of reasons. 1. Very hard to read the driver diameter because scale of ruler is almost microscopic and determining the exact diameter is difficult. 2. Operating an engine at maximum speed over a length long enough to measure maximum speed is asking for an engine on the floor. 3. I've changed the settings all over the place and have yet to get it to work at real slow speeds. Which is where it's most noticeable. I came across Locosound that builds sound decoders for European engines, wanted to buy one but havn't found a good US whistle yet. Anyway they have a similar CV only they go about the process differently. Their formula is to activate 128 speed steps. Drive loco at speed step 1, measure the time in seconds that the driving wheel takes at this speed to complete a revolution. Divide the time by 0.02304. Enter that value into their CV #52 and half the value into CV #53. I understand that Soundtraxx uses CV #54 for exhaust sync rate and CV #55 for exhaust note control so the two companies are not compatible in that sense. However both systems are basically 'time/ speed/ distance' equations. Sndtx uses diameter, while LS uses circumfrence, Sndtx uses top speed and LS uses slowest speed. I also realize that the constant factor will have to be changed and that might take some 'fudging' around. The question is: Can someone help rewrite Soundtraxx's formula using the Locosoud parameters? I would rather run my loco slowly than at max speed. I've posted this also to the 'Pit site.
Chris, here are some things to start out: I will assume HO. Also, the more places past the decimal you calculate with, the more accurate your final answer will be. Usually .000 is accurate, and .0000 is precision, so be careful in rounding off when trying to check figures. I do not have a divide sign on this keyboard, so I'll use the (/) sign for that here. HO is 3.5mm = 1 foot so, 3.5mm divided(/) by 25.4 = .137795276" (.138" = 12") and, .138 / 12 = .01148 (.0115" = 1") (Note: the wheel flange is 1" wide and 1" long on real railroad wheels, yet the NMRA says we should fudge it to .028", so some poetic license may be taken at times and considered still SCALE.) Circumference = Pi(3.1416) x diameter. Say we have an HO steam engine driver that is reported to be 5 feet in diameter (60"). But when we measure it with a micrometer caliper, it is actually an HO scale 63". All wheels MUST be the same diameter, or we have a problem engine, so I'll go with 63" diameter. [ .01148 x 63 = .72324" diameter ] Cir. = 3.1416 x .723 = 2.272130784" (2.272") traveled per revolution of this driver. Follow me? OK. We know you will have to have four chuffs for each time the driver rotates one revolution. What part of a mile is one revolution of this driver? One HO foot (.137795276) x 5,280 feet (one mile) = 727.5590573" (one HO mile). or divide that by 12 to get (60.62992144') one HO mile in actual feet, see? Now you want to know how many times is this driver going to turn over in one mile, so you can calculate the speed later. So: How many circumferences is in one HO mile? Use inches. 727.559 / 2.272 = 320.228 revolutions, and, x4 = 1280.9 chuffs per mile, see? ( Shays will have 3 chuffs per rev and 4-12-2's will have 6 chuffs.) Their formula says to activate 128 speed steps, but they are only concerned with step #1 setting for speed so you can time only one revolution. OK Since we know a switcher with 33" drivers and a Pacific with 80" drivers will travel differently for one revolution, lets assume that step #1 is for coupling up to your crack passenger train, so you want to go very slowly. What is slow? Well if it takes one second for the 63" driver to rotate one revolution, then it has traveled 2.272" which is also one 320.228th of a mile. RULE: "Up to 2 miles an hour is a couple, but at 4 miles an hour, it is a collision!" With that in mind lets say that is still too fast for an acceptable couple, so lets figure it takes 4 seconds to go the 2.272", that may be OK for a switcher whose drivers are only .3789" (33") diameter, but still way too fast for the Pacific's .9186"(80") drivers. Each engine will have to be slowed down to "slow enough" for the #1 step. That will be up to you to determine. Now they want us to divide the TIME by 0.02304 and enter THAT value into their CV#52 etc.... So our ONE second speed divided by 0.02304 = 43.402777.... factor (and half that for CV#53.) Our 4 sec / .02304 = 173.6111...etc. Remember: when you run any HO engine at a speed that covers 727.559" and do that in 60 seconds, your engine is traveling at a scale one mile a minute, which is 60 miles an hour scale speed! If you get a TGV and travel 60.6 actual feet in only 30 seconds, your TGV has just hit 120 scale miles per hour! All this is good for diesels too. All you need is a dial caliper to measure the wheels and a calculator. Guessing with a ruler will not be very close, which could prevent running a double header, see? Enjoy!
I find it easier to think of 60 scale miles per hour as 1 foot per second. as per above - 60 seconds to travel 727.559 is a mile a minute. 727.559/12 is 12.1260" per second (that .1260 is darn close to 1/8 inch) Anyway - on HO it is usually easy to find 12" things on the layout (a number 6 switch for example) and as you pass over it count your "onemississippi" or whatever and you can tell quickly if you are running a good scale speed. (in N it should take you two seconds to pass 12 real life inches for scale 60mph)
You are right Rob, I just gave the accurate stuff because Chris is trying to set the driver rpm to speed to obtain the correct chuff settings for any diameter driver. Just figuring for HO you are right, a mile a minute is a real foot per second (about), 6" per second is about 30 miles an hour, so one inch per minute is about 5 miles an hour, .50"/sec = 2.5mph, .25"/sec = 1.25mph, 0"/sec = dead engine! [ 25 June 2001: Message edited by: watash ]
Yes, I strayed a little from the original topic. I sure am glad us dezul modelers don't have to time our chuff-chuff sounds with driver size However I love the hissss sound you can get when your steam engine comes to a stop (the DCC / Sound combos are just briliant) As for the OP - I have no idea if you can reprogram the Soundtraxx meathod. However, I can tell you that the only way to get an accurate driver diamater measurement is with a caliper.
