I've watched and listened to operators using the Proto Throttle, and they say the start up, moving, acceleration, breaking, all feel much more realistic. One of the participants was an engineer.
I've never operated one, and probably won't, but the way they describe it, it reminded me of the IC Hogger power pack with teathered walk around throttle. It had momentum and breaking features that took some time to get used to. I still have it, haven't used it since the last plywood central.
It was nothing like the conventional power pack.
With my small layout, I'm happy with what I have, but watching the demo of the PT was impressive.
Mike.
My You Tube
thanks for the comments
rrinkerYou can do it today in the loco by implementing a speed curve that is not linear, but again then it is fixed no matter what the loco is going - moving light, moving a small train, or moving a train close to its maximum capacity.
yes, a more logarithmic speed curve, where each speed step gets smaller might model this behavior better than constant acceleration rate programmed into CV3.
My understanding of the use of acceleration rate is to delay each speed step change by an amount proportional to CV3.
The plots show a relatively sharp rise in speed and then each increase is substantially delayed for lower HP locos.
rrinkerThe decoder can measure the load ont he motor via BEMF, and a limit could be established to simulate both the maximum horsepower as well as tractive effort (often the limiting factor when starting out).
BEMF isn't necessary unless you want to account for grades. The current speed step is known to the decoder.
rrinker I think you could also do this in the throttle, but it would be more of a preset simulation and you'd need to change it if you drop the entire train and then move the same engine(s) light.
I think there should be separate values for tonnage and HP. HP could be programmed into the decoder. Tonnage should be set for each train in the throttle and would need to be communicated to the decoder.
If this were implemented in a decoder, the loco would presumably start from zero if it lost power, a glitch that causes the processor to reboot. If this were implemented in a throttle, if the loco lost power it would start at the speed dictated by time since the throttle was increased. A keep alive would help in both cases.
doctorwayneAl Krug did a nice article on tractive effort vs. horsepower.
I posted a link to the rectangular hyperbola curve showing tractive force vs speed.
the plots show the effect of tractive effort on speed over time (i.e. acceleration).
Track fiddlerWow that's one large burst of technical data
the plots summarize the data
Track fiddlerYour locomotive or locomotives start to creep very slowly and accelerate up to your command in a realistic time frame.
the plots show that a train actually accelerates (gains speed) quickly from being stopped, but acceleration diminshes and it takes longer to get to full speed.
http://www.n0kfb.org/rail/railphs.htm
thanks for posting. It actually mentions F=ma. it touches several issues: max speed, grades, max tractive effort, ... w/o really summarizing
I think Randy's comment was succinct
rrinkera small 1200HP switcher can move a huge cut of cars ... but the switcher can't get that cut much above 15MPH while the pair of 3000HP road units can move it along at 60MPH.
i've read more than once that horsepower is speed
interest in the ProtoThrottle suggests modelers are interested in more realism. Not sure if that interest is in looks or performance. The ProtoThrottle includes code to specify tonnage that could be used to model acceleration as the plots suggest. They indicate it's a future feature.
greg - Philadelphia & Reading / Reading
doctorwayneAl Krug did a nice article on tractive effort vs. horsepower. Unfortunately, I can't seem to find it on-line.
"One difference between pessimists and optimists is that while pessimists are more often right, optimists have far more fun."
You wouldn't want to use a dcc setup that replicated the real acceleration rates of locos hauling long and heavy trains. You'd be pulling your hair out waiting for the thing to get up to normal speed -- if you'd get there at all.
Running the Conrail SEOP (Selkirk-Oak Point) some nights, with a longish train (say, 120 loads), on the table-top flat Hudson line going south, the engines would be in the 8th notch continuously and it would take 15 miles to begin to edge up close to track speed (50mph). That was with 3 B23-7's, all they gave you for that run.
After dropping cars at Poughkeepsie and Croton -- down to, say, 60 cars -- they'd run much better!
Wow that's one large burst of technical data, ... I will give you that.
In scale modeling, I will just call it momentum. My brother and I had this capability in the later part of the 70s when we were still teenagers.
You get set up with the right Transformer, or build one like we did. Then you just crank the knob on your power pack. Your locomotive or locomotives start to creep very slowly and accelerate up to your command in a realistic time frame.
Careful though, they stop doing the same in a more prototypical fashion like your data in reverse I suppose. It takes some getting used to. They have them with a break option but would be unrealistic at this point
If you ever over shoot your destination, you might as well back up and try again.
Locomotives take awhile to start and take even longer to stop.
Just my thoughts.
Al Krug did a nice article on tractive effort vs. horsepower. Unfortunately, I can't seem to find it on-line.
I have a copy of it, but it's rather lengthy and perhaps it's not suitable that I re-post it, as it's not my material. A more thorough on-line search may get you better results than my quick look.
Wayne
Hmm, I don't see why this couldn't be implemented with DCC. But not int he throttle. The decoder can measure the load ont he motor via BEMF, and a limit could be established to simulate both the maximum horsepower as well as tractive effort (often the limiting factor when starting out). For older locos you would need feddback to the throttle to light up the wheel sli indicator, whereas in many modern locos you can just (assuming indestrucbile drawbars) just open it wide up and the control system will push as much power to the wheels as it can without slipping.
Hmm, good reason to build a DIY decoder, so you cna experiment siwht using the BEMF data, and a couple of the available CVs to enable/disable this feature and to set the limit. You'd basically want to program in somethign that reprsents toe HP of the loco, as well as the maximum TE - a small 1200HP switcher can move a huge cut of cars that might require a pair of 3000HP road units - but the switcher can't get that cut much above 15MPH while the pair of 3000HP road units can move it along at 60MPH. Low gearing and a higher TE to HP rating help the little guy do its work.
I think you could also do this in the throttle, but it would be more of a preset simulation and you'd need to change it if you drop the entire train and then move the same engine(s) light. You can do it today in the loco by implementing a speed curve that is not linear, but again then it is fixed no matter what the loco is going - moving light, moving a small train, or moving a train close to its maximum capacity. Actually, this has been somewhat mentioned in the past, using 3 step speed curves (or even the full 28 step tables) to configure some engines for faster response at the low end of the throttle and others for slower response at the low end. Uually discussed in terms of a drag freight loco vs a passenger loco. One example - lots of railroads used Trainmasters on commuter trains because of their high power and ability to get the train up to sped quickly after each station stop - critical in an all stops local.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I'm trying to get a better understanding of horsepower and train acceleration. looking for quantitative confirmation.
the plots shows train speed v. time for 4 loco horsepower values: red 3000 HP, orange 2000 HP, cyan 1500 HP and green 1000 HP. Raw results are also listed.
horsepower is a measure of work, lb-ft, per unit of time, minutes. This is equivalent to the product of force, lb, and speed, feet per min. My understanding of this is the tractive effort, the tangential force of the wheel on the rails is equal to the horsepower / speed. This means the force decreases with speed (the work is the same because a greater distance is traveled in the same amount of time). (The rectangular hyperbola mentioned in previous threads).
the plots also account for a maximum tractive effort of 70,000 lbs assumed for 150 ton locomotive
the plots indicate speed (vertical axis) in mph vs time in minutes (horizontal axis). The red curve, 3000 HP case, quickly reaches >30 mph w/in 5 min. ~7.5 mins. for 2000 HP (orange) and ~27 mins. for 1500 HP (cyan). The 1000 HP case (green) never exceeds ~24 mph because of insufficient HP.
the simulation also accounts for train resistance due to friction and aerodynamic drag as described in Armstrong's book, "The Railroad". His tables indicate that resistance increases from 2.3 lbs/ton @ 10 mph to 10.4 @ 70 for fully loaded cars and 4.5-19.8 lbs/ton for empty cars. This sim uses resistance for a fully loaded cars.
since the resistance increases with speed and the force from a constant horsepower decreases with speed, there can be a point where both are equal and no further increase in speed is possible. That is why the 1000 HP case does not reach 30 mph.
while the numbers may not be completely accurate, I believe the trends are. They show that acceleration is not constant. For limited horsepower, as in the 2000 HP case, it took just a few minutes to reach 15 mph, but an additional 20 mins. to reach 30. I think it would be interesting if our DCC throttles implemented this behavior instead of constant acceleration rates.
the following lists values for each point of each curve. Assuming a starting speed of 1 foot/sec, acceleration is calculated for each time period (1 min) and the speed is adjusted.
the mass is in slugs (lb / 32.2) for what Armstrong reported as an average tonnage of 4760 tons for a train.
lb/ton is the resistance for the current speed and lbFres, lb-force resistance, is the product of resistance and tonnage (e.g. 1.6 * 4760) and increases with speed
lbFloco, lb-force for the locomotive is the tractive effort (33000 * hp / (60 * fps)) limited to 70,000 lbs
the net force is lbFloco - lbFres
acceleration, ft/sec^2, is the mass / lbFnet
ft/sec is the accumulation of the product of acceleration and time: fps += 60 * fps^2
mph is fps * 3600 / 5280
#min mph ft/sec fps^2 lbFnet lbFloco HP lbFres lb/ton mass tonnage 1 9.3 13.61 0.210 62156 70000 1000 7843 1.65 295652 4760 2 13.4 19.64 0.100 29690 40399 1000 10708 2.25 295652 4760 3 15.6 22.87 0.054 15926 28004 1000 12077 2.54 295652 4760 4 17.1 25.15 0.038 11235 24047 1000 12812 2.69 295652 4760 5 18.3 26.88 0.029 8537 21867 1000 13330 2.80 295652 4760 6 19.3 28.25 0.023 6734 20457 1000 13723 2.88 295652 4760 7 20.0 29.35 0.018 5434 19468 1000 14034 2.95 295652 4760 8 20.6 30.26 0.015 4450 18736 1000 14285 3.00 295652 4760 9 21.1 30.99 0.012 3627 18177 1000 14549 3.06 295652 4760 10 21.5 31.60 0.010 2980 17745 1000 14764 3.10 295652 4760 11 21.9 32.10 0.008 2464 17406 1000 14941 3.14 295652 4760 12 22.2 32.51 0.007 2047 17134 1000 15087 3.17 295652 4760 13 22.4 32.86 0.006 1706 16915 1000 15209 3.20 295652 4760 14 22.6 33.15 0.005 1427 16737 1000 15310 3.22 295652 4760 15 22.8 33.39 0.004 1196 16591 1000 15394 3.23 295652 4760 16 22.9 33.60 0.003 1004 16470 1000 15465 3.25 295652 4760 17 23.0 33.77 0.003 845 16370 1000 15525 3.26 295652 4760 18 23.1 33.91 0.002 712 16287 1000 15575 3.27 295652 4760 19 23.2 34.03 0.002 600 16218 1000 15617 3.28 295652 4760 20 23.3 34.14 0.002 506 16160 1000 15653 3.29 295652 4760 21 23.3 34.22 0.001 428 16111 1000 15683 3.29 295652 4760 22 23.4 34.30 0.001 361 16070 1000 15708 3.30 295652 4760 23 23.4 34.36 0.001 305 16036 1000 15730 3.30 295652 4760 24 23.5 34.41 0.001 258 16007 1000 15748 3.31 295652 4760 25 23.5 34.46 0.001 219 15982 1000 15763 3.31 295652 4760 26 23.5 34.49 0.001 185 15961 1000 15776 3.31 295652 4760 27 23.5 34.53 0.001 157 15944 1000 15787 3.32 295652 4760 28 23.6 34.55 0.000 133 15929 1000 15796 3.32 295652 4760 29 23.6 34.58 0.000 112 15917 1000 15804 3.32 295652 4760 color=cyan next #min mph ft/sec fps^2 lbFnet lbFloco HP lbFres lb/ton mass tonnage 1 9.3 13.61 0.210 62156 70000 1500 7843 1.65 295652 4760 2 16.2 23.74 0.169 49889 60598 1500 10708 2.25 295652 4760 3 19.2 28.15 0.074 21744 34753 1500 13009 2.73 295652 4760 4 21.3 31.26 0.052 15294 29305 1500 14011 2.94 295652 4760 5 22.9 33.60 0.039 11553 26395 1500 14841 3.12 295652 4760 6 24.2 35.43 0.031 9027 24553 1500 15526 3.26 295652 4760 7 25.2 36.90 0.024 7222 23283 1500 16061 3.37 295652 4760 8 26.0 38.09 0.020 5869 22358 1500 16489 3.46 295652 4760 9 26.6 39.07 0.016 4822 21659 1500 16837 3.54 295652 4760 10 27.2 39.88 0.014 3993 21117 1500 17123 3.60 295652 4760 11 27.7 40.55 0.011 3327 20687 1500 17360 3.65 295652 4760 12 28.0 41.12 0.009 2786 20343 1500 17557 3.69 295652 4760 13 28.4 41.59 0.008 2341 20063 1500 17722 3.72 295652 4760 14 28.6 41.99 0.007 1973 19834 1500 17861 3.75 295652 4760 15 28.9 42.33 0.006 1667 19645 1500 17978 3.78 295652 4760 16 29.1 42.62 0.005 1411 19488 1500 18077 3.80 295652 4760 17 29.2 42.86 0.004 1196 19357 1500 18160 3.82 295652 4760 18 29.4 43.07 0.003 1016 19247 1500 18231 3.83 295652 4760 19 29.5 43.24 0.003 863 19155 1500 18291 3.84 295652 4760 20 29.6 43.39 0.002 734 19077 1500 18343 3.85 295652 4760 21 29.7 43.52 0.002 625 19012 1500 18386 3.86 295652 4760 22 29.7 43.63 0.002 533 18956 1500 18423 3.87 295652 4760 23 29.8 43.72 0.002 454 18909 1500 18455 3.88 295652 4760 24 29.9 43.80 0.001 387 18869 1500 18482 3.88 295652 4760 25 29.9 43.87 0.001 330 18836 1500 18505 3.89 295652 4760 26 29.9 43.92 0.001 282 18807 1500 18524 3.89 295652 4760 27 30.0 43.97 0.001 241 18782 1500 18541 3.90 295652 4760 28 30.0 44.01 0.001 205 18761 1500 18555 3.90 295652 4760 color=orange next #min mph ft/sec fps^2 lbFnet lbFloco HP lbFres lb/ton mass tonnage 1 9.3 13.61 0.210 62156 70000 2000 7843 1.65 295652 4760 2 17.5 25.65 0.201 59291 70000 2000 10708 2.25 295652 4760 3 21.6 31.62 0.100 29447 42890 2000 13442 2.82 295652 4760 4 24.3 35.65 0.067 19836 34784 2000 14948 3.14 295652 4760 5 26.3 38.64 0.050 14732 30856 2000 16124 3.39 295652 4760 6 27.9 40.97 0.039 11471 28469 2000 16997 3.57 295652 4760 7 29.2 42.83 0.031 9173 26851 2000 17677 3.71 295652 4760 8 30.2 44.34 0.025 7462 25684 2000 18221 3.83 295652 4760 color=red next #min mph ft/sec fps^2 lbFnet lbFloco HP lbFres lb/ton mass tonnage 1 9.3 13.61 0.210 62156 70000 3000 7843 1.65 295652 4760 2 17.5 25.65 0.201 59291 70000 3000 10708 2.25 295652 4760 3 24.5 35.98 0.172 50893 64335 3000 13442 2.82 295652 4760 4 28.6 41.99 0.100 29645 45865 3000 16219 3.41 295652 4760 5 31.6 46.32 0.072 21316 39293 3000 17977 3.78 295652 4760