Diesel acceleration

Discussion in 'Getting Started' started by Cactus, Oct 29, 2001.

  1. Cactus

    Cactus Member

    I bought an MRC Tech-4-220 power pack for my N-scale layout. It's cool, allowing me for the first time to operate my locomotive at less than 100 mph.

    Now, the 220 has a "momentum" control and a "brake" control, which supposedly allow more realistic train control.

    The brake is a no-brainer. It lets you stop the train when and where you want.

    It's the momentum control that I have a question about. I've found three ways to use it. Let's say that I want to move my GP-38 through the yard at 20 mph.

    1. With the momentum switch off, I adjust the throttle to the 20 mph setting and the train almost instantly reaches that speed. Fast response, but not like the prototype.

    2. With the momentum switch on, I adjust the throttle to the 20 mph setting. The train only starts to move after 5 seconds, or so. It begins to creep imperceptably at first, then VERY slowly accelerates to 20 mph, taking 20 or 30 seconds to get up to speed.

    3. With the momentum switch on, I adjust the throttle to the 150 mph setting. I leave it there until the train begins to move, after about a second. Then I quickly lower the throttle to the 20 mph setting, and the train quickly and smoothly accelerates to to 20 mph, taking only three or for seconds to reach that speed.

    My question: How would an engineer on a prototype GP-38 handle his/her throttle? Do these locomotives require operation more like scenario 2, or 3? Any opinions?

  2. justind

    justind Member

    In watching these locomotives at the local yard (keep in mind that they don't use switchers, so it is pretty cool to watch 3 UP triple axels moving only 10 or 12 cars into place) it seems like they do "gun" the throttle until the engine starts to move and then slack off again. However I know very little about controlling the prototype so I can't elaborate further.

    I like the sound of your power pack...how much was it? Is it DCC or not, and how well do you like it?
  3. Cactus

    Cactus Member


    I like it a lot. The thing I had before was one of those el cheapo units sold with Bachmann train sets back in the '60's. It was that old, and whatever fine control it once had has long since bitten the dust. It now supplies control to my turntable motor.

    I bought the Tech 4-220 a couple of months ago. I bought it on special sale (I think from Internet Hobbies). Paid a little under $50 for it, I think. You can still get one from them, but I think the price is now just over $50. (I paid maybe $48)

    I generally use it with the momentum switch set to the "on" position, following scenario number 3. This gets the train moving soon after I advance the throttle, but still gives me a nice gradual acceleration. I was just wondering if the prototype locos also "gun" their engines a bit to get started.

    By the way, the momentum control also gives you prototypical deceleration. It surprised me at first to see how long my trains took to coast to a stop, and gave me an appreciation of the advantage dynamic brakes must have been when the railroads got them.

  4. justind

    justind Member

    I found one on www.internettrains.com for $47...MRC tech 4 220...that is the one with the single knob and 3 switches? I believe I was looking at the right one. I like the sound of it, I will see if I can't talk my wife into it. ;) . Right now I am using a Life-Like basic powerpack that comes with all of thier retail sets. It works, but my cheaper diesels and even my more expensive
    2-8-0 have a lot of problems with low speeds. And they all leap to that 50mph instantly...talk about whiplash.
  5. BDC

    BDC Member

    Another consideration...

    Justind- If you can find one priced just right, you might look at the Tech 4-350. Has all the same options of the 220, except that you can program the acceleration rate, max voltage applied to the track (which really helps with slow-speed operations.) It has a few other capabilites, but the price does reflect it. You might be able to find one for around $75-80. Good luck with the wife...
  6. N Gauger

    N Gauger 1:20.3 Train Addict

    Momentum control

    Cactus; I think that both ways (20 & 150) are correct. The "Big Guys" work just about like 18 wheelers. The more load you have, and the more "Clear Way" you have the faster you can get -Up To Speed.
    It all depends on the situation. Ex.: I have a friend that used to drive GG1's. He was watching a "rookie" engineer take a bunch of ore cars out of a yard. The new guy did your trick with the throttle "up to 150" and Guess what??? -- He derailed about a dozen cars... Not good eh????
    But, if ya do it the 20 MPH way - you go up to speed slooooow & nothing de-rails. (especially through switches & curves.
    Also remember momentum was designed after it appeared on a "want list" of model railroaders. The "On / Off" controllers are not too good for switching operations and they (we) wanted more realistic operations.
    You'll also learn that the trains STOP slowly. So if you are heading on to a siding, you gotta turn the throttle to 0 at "just the right moment" so the cars don't accordian when you hit the brake. - Just like the real engineers have to learn. Above all else - enjoy your new toy!!! ---- N gauger
  7. LC

    LC Member

    2 is the most correct, it takes quite a bit of time for power units to get enough built up to move, even if it's a light move.

    Thats why they "gun it" and then back off, like wise it takes time to slow the power down, making option #2 still the correct one.

    Sounds like you have a very good power pack there, I'll have to look into it. Does it have enough power to run five or six units at a time?
  8. justind

    justind Member

    Tech4 240

    Hello Cactus,
    I was on another board asking about this powerpack and someone who had owned a 240 mentioned some interesting things. He said:
    The way you were talking about your controller it doesn't sound like it was this way. While I am looking to invest in a new controller I thought I would check into this...
  9. Cactus

    Cactus Member

    I screwed up some how just now and lost the reply I was posting. I'll compose it again here and hope not to have introduced a duplicate message on the forum.....

    justind -- Yes, the 220 is the one I have, and I love it.

    No, it's not DCC, but I don't currently have a DCC-sized budget.

    I think I'd have bought the 350 but couldn't at the time justify the extra bucks for the extra features. The juice didn't seem worth the squeezin' just then. I'm still putting my effort into building the layout (Peco turnouts aren't cheap).

    Yes, it does use pulse technology at slow speeds. I have found no objectionable vibration in my Atlas GP-38. I can hear a small vibration just as the loco is starting, but nothing that bothers me at all. I don't know that I'd want to run the thing at 2 mph for a half hour, but that would be the case for any electric motor run at slow speed with any power supply. I'm happy as a clam with it.

    The GP-38 is my only locomotive, so I can't say how other models would sound with the pulsed supply. There is a new Lifelike BL-2 somewhere in my home, but my wife intends to surprise me with it for my birthday in several weeks.

    My choice seems to be either to stay young or increase my rolling stock. Somehow the birthday is looking pretty good!;)
  10. gibbs

    gibbs New Member

    I've got two Tech4 260s and they work like a charm. Never had a problem with excess viabration on any of my engines. (IHC 4-6-2 Pacific & 2-6-0 Camel Back, Spectrum GP-30 and LL Proto 2000 GP-9).
    I use both methods 2 and 3 depending on how fast I want to accelerate. As for realism, I'm thinking a real loco has a lot more control of his power than just one throttle.
    Got to mention the 'brake' button on the power pack that helps slow/stop the train while maintaing the momemtum aspect.
  11. brakie

    brakie Active Member

    The GP38 like all EMDs takes time in moving,the engineer will work his throttle from the frist notch to the 2nd,then to the 3rd notch, you can not load a locomotive to quickly,so it takes time to move the engine and train.If you load the engine to quickly you will burn the traction motors.So, you would want to use the 2nd scenario
  12. Cactus

    Cactus Member

    Thanks, Brakie.

    I'm listening.
  13. billk

    billk Active Member

    Cactus -
    In view of Brakie's information, for more prototypical operation you need to modify your controller so that if you change the throttle settings too rapidly, your loco gets zapped with 120vac. Please share any royalties if you patent this idea.:rolleyes:
    - Bill
  14. brakie

    brakie Active Member

    Cactus:Glad to have help you.Question:Do you have any ALCOs?You see a ALCO had a different response to the throttle then EMD.When you would release the brake on a ALCO and put the reverser in forward or reverse and open the throttle you would start to move.That black smoke that belch out of a ALCO was cause by tubro-charger lag in response to the throttle.You did not see this with early EMDs as they were non tubro charged How ever if oh,say a GP-9 was ideling for awhile you would see a wisp of blue smoke from fuel build up,when you open throttle.:)
  15. Cactus

    Cactus Member


    Nope, I own just the one locomotive -- a GP-38, though a BL-2 will appear soon...

    An Alco may show up early next year, we'll see.



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