I think I know the answer to this. I am setting the top speed of some road switchers to something realistic as they run without any cars on the flat. However, this is seriously going to impede their chances of hauling a good string of properly weighted cars up my steepest grade, right?
It not like I am changing gears and I will still have the torque at the lower speed is it?
So whaddya all do? Set your top speeds with a typical train in tow?
Should I be content with whatever # of cars they can haul up the grade at prototypical full power? (My grade is a little steep. I am building a bypass loop at the moment.)
I suppose the obvious thing to do is get 3/4 throttle to the protypical top smph and leave some power in reserve. I’ll just consider the 3/4 throttle as full power.
A really clever DCC decoder will hold motor speed constant even if the load on the motor changes. Such a clever decoder would look at the motor’s back emf and when it saw the back emf drop off, the decoder would put more current into the motor to keep the speed, and hence the back emf, up.
I don’t know how clever the decoders are these days, and one must assume they get cleverer as time goes on. I’d experiment. Set the top speed to something reasonable, and see how many cars the locomotive can haul up your ruling grade. Reset the top speed to “high-as-it-can-go”. See if it can pull more cars set that way. Let us know how it comes out.
Many decoders (Digitrax and TCS for example) have “Back EMF” which is sort of like “cruise control” on your car. If you have a train running at a scale 25 MPH the decoder will increase or decrease the amount of power going to the motor so the train will maintain that speed whether going uphill or down. So if say going uphill it can apply more power than what the top speed is that you set, if that’s what is needed to keep the train at the speed you set. Of course, it can only go up to the maximum total power the engine has. If the train’s too long or the grade too steep, it will stall or just spin it’s wheels, just as it would on DC at full power if it couldn’t pull the train.
With most decoders it’s automatic based on the CV’s (you can set whether you want to use it or not, and how much it should compensate - you might want to let a train slow down a little going uphill or speed up a little going downhill). However with BLI engines with QSI sound / decoders you have to hit an F-button to turn it on and off.
Remember too that you can use CV’s to “speed match” engines, so if you have a long train you can add several engines to the consist, and have them all start, run and stop together…so you’re not limited to how much one engine can pull by itself.
If you encounter too much wheel slip going up grades, your trying to pull too long of a train. Most trains get drug down or slowed down by the grade. If you want your trains to run prototypically you should use just enough power to keep the train moving up hill.
They would start up at normal or just above normal speed and then the weight the rest of the train would start slowing the train down as the train had to pull more of itself up grade. On level ground the train would pull more cars at greater speed because it only needs to over come wheel drag. On the up hill grade the weight of the train will pull it down as the weight over comes the wheel drag. On the down hill grade the weight tries to push the train as the weight over comes the wheel drag.
So yes it would be good the set your train top speed about a 1/4th to ½ below full power to help you get up grade, but remember that while going up at full speed power you may pop a coupler or two from the strain on them. To keep from popping couplers I would get a little bit of a running start at a steep up hill grade and slow down early for a steep down hill grade.
The up hill grade well slow the train down before it gets to the top of the hill, so the train speed is close to or below normal speed at the top of the hill and slowing down before a down hill grade will keep the train from running away before it reaches the bottom of the down hill grade.
They would stop at the top before descending for a brake check and double or triple up to get a train up the grade then reassemble it at the top of the grade.
I should have said: I am working on the speeds of a half dozen FM 16-44s which I found out were not able to be MU’d (no wonder there are no hoses).
My other locos are in the process of being speed matched for consists up the grade…but there too, I am going to leave a little untypical top end speed after the 3/4 throttle mark.
I’m afraid I use mostly NCE D13SRs which I don’t think have any load compensating features. I needed a lot of inexpensive decoders to do the collection. Although the H16-44s all have Digitrax 123s, so there might be something there for load. I will have to read about it.
Lots of us equate speed and power (read: horsepower and torque) from our experience driving internal combustion cars & trucks. An IC engine has HP (speed) and torque (grunt) curves that increase as engine RPM increases. An electric motor, in both 1:1 and model scale, can have max torque from zero RPM up. That is why diesel-electrics were developed and still rule the rails today.
That being said, physics plays a big part in getting mass over the hump. A higher degree of momentum (speed) will carry you faster and (perhaps) further up a hill, before gravity overwhelms tractive ability. So if you are running the cannonball express, set your speed high and you’ll probably roar up that incline. If, however, you want to represent the prototypical world, set your level speed at something approximating scale RR speed and appreciate your locos slowing down and working hard to get up that incline. That’s more like real railroading.
I find that If I give my engines high power with a heavy train, they’ll spin the wheels going up a hill. However if I slow down I can actually make it up. (when it spins wheels, it still goes the same speed when it’s not)
As I remember, FM 16-44s could be MU’d with each other, but were not compatible with EMD and ALCo. I’m missing a lot of brain cells now (child of the 60s-70s) so I could be wrong.
Not unless you use so little power that the model stalls out. That’s why it’s a good idea to be wary of traction tires - they are a lot more prone to reaching zero RPM rather than spinning.
Full scale traction motors have a one-hour current rating - they will overheat if that level is held for one hour, quicker if it is exceeded. If we were to operate a model locomotive at its one hour rating and it could take a train up a 2% grade, the resulting grade would be 606 feet long and 12 feet from base to crest. Maybe at Northlandz, but highly improbable for a home layout.
My own locos (except for one with a traction tire) will spin long before current reaches the overheat level, and I don’t let them stall.
more current to the motor allows more motor torque to be generated. Current depends on clean electrical path, and current available from the power supply. Assuming those are not limitations, the motor draws the current it needs to increase torque until it either overheats, or has reached maximum torque that particular motor is capable of producing. In HO scale and smaller, motor torque/maximum current is usually not a limitation unless traction tires are used.
tractive effort. In an HO locomotive without traction tires, the maximum pull is usually limited by locomotive weight and balance. For a typical HO diesel, you can expect pull to be 20% or less of the locomotive’s weight. The more weight, the more train that can be pulled before driving wheels start to slip. Keeping the weight balanced allows all driving wheels to start slipping at the same time. The locomotive is only as good as the tractive effort of the most slippery driving wheel. Once one wheel starts to
DEPENDS: ‘‘Reducing’’ Voltage slows things down, as does inadequate Amperage from your power supply. A ‘grade’ increases LOAD, which pulls more AMPS from your supply__*__.
EVERYTHING slows down going up a hill - including people - because it takes more effort.
Engineers ramped up power - even changed gears - to compensate, so why cant you? Additional Engines were added to increase needed horsepowe for the load being pulled. My guess is your 3 FM 1644’s will be enough to pull anything you have - maybe even two.
You are dealing with models here, so MU hoses are fake. Couplers are really doing the work.
IF your FM’S are same models from same production run, they should MU together, If not, use your CV’s.
__*__6 Atlas FM 1644’s should full around 1.5 amps, total (18VA). What is yours? I you want to know how many amps you are using at any given time, a DC ammeter will tell you. With DCC it’s more of a problem
MY GUESS: If your trains are slowing down on a grade too much, it’s too steep
The grade is only too steep if the locomotive can’t take itself and one car to the top. If the assigned power can’t take the specific train up the grade, send out a helper or several. Next time, assign enough power for the job.
In the waning days of steam, doubleheaded Y-6s would hit the bottom of a 1.4% grade as fast as dynamic augment would allow - about 50mph. Close to the summit they would be down to 10mph and blasting cinders 100 feet into the air on minimum cutoff - and the Y-6b would have gone from compound to simple expansion. I wonder if any of our N&W modelers accurately model the speed aspects of that kind of operation (I know they can’t model the cinder blast, and only a theater-size subwoofer could begin to do justce to the sound…)
Chuck (modeling Central Japan in September, 1964 - with pushers on the 2.5%)
Now, Fred, that is really interesting. Hitting the throttle at the bottom of the grade will help, but be unrealistic if the Vmax is set above prototypical speed. But hitting the throttle on the grade when momentum is lost, will not have any effect (although I think one would almost always see an effect [increase in pulling] because is would be quite a long or steep grade for a loco to loose all additional run up momentum before hitting the crest.)
My grade is not that severe i.e if I hit prototypical max speed at the approach I do not lose complete momentum on the grade, The loco is it still slowing down on the crest as it brings the first of say, 10 cars over, but has not reached a constant slow speed. Thanks a lot, all you guys. This has been an really interesting thread. [wow]
Keep in mind that even if the prototype engines didn’t have m.u. capability, real railroads in that situation did in some situtations run a diesel double-header - two engines running together but each with their own engineer and fireman. If you do that on the model railroad, you don’t have to pay for the extra crew’s time, so why not?? [:)]
Otherwise you could have one of the FM’s on the front of the train, and cut in another one ahead of the caboose as a helper. That would be a more common situation where two diesels on the same train would not be m.u.'ed and would each have their own crew.
As far as how many cars each engine can pull, I would work backwards. Get the engines so they’re running good, and then work out how many cars they can pull up the grade. Subtract one to give you a little safety margin, and that’s how many cars one of those engines can pull up the grade. If it’s say 8 cars and a train is 10 cars long, it’ll have to get a helper or you’ll need to assign another engine or engines to the train. That’s how real railroads do it. Now it’s true the real engine could probably pull more cars than that, but remember our trains are shorter than the real ones. In my railroading, one Atlas GP can haul a mainline 30 car ore train for example, as could the real engine - but it doesn’t look right, because real mainline ore trains use 2-3 diesels and are 100+ cars long. So I’ll use a GP for switching 10-15 ore cars at a time around the yard, or up to the ore dock, but for a mainline train I use two engines. Even if I could do it with one, it looks better with two.
I looked on-line at some pictures of FM H 16-44s from different railroads. Some had MU hoses and some didn’t. It may depend on your prototype, if you have one. MU capability could be an option that some wanted and some didn’t.
I am pleased, as I picked up all those H16-44s to run in tadem or triplets–3 ATSF–one each of NW, PRR, CP. Even if I can’t find evidence of MU’ing on a particular rr, I’ll pretend they hired the crews required. Thanks for the info.
BTW just tried adding more power beyond prototypical speed to a FMH-16 with no more momentum on my grade (with a dozen 50 foot boxcars)–no surprise–as told to me, there was no more umph to add. It just started spinning.