GP35 Gearing Question

Discussion in 'GP35' started by adams, Feb 10, 2018.

  1. adams

    adams QLA-QSF

    Hello All—-I was reading that the Frisco GP35’s that had the AAR trucks had slightly different gearing than the EMD trucks/motors. How would that affect a multiple unit lash up with other EMD’s? Wouldn’t the 35’s wheels want to turn at a different rate with the same current draw all the locos were getting? I know all sorts of locos with different gearing have been lashed up, but I guess I just don’t understand the specifics. Thanks, Chris
  2. Karl

    Karl 2008 Engineer of the Year Supporter

    I believe that we a prone to equate the gearing of diesel locomotive to an automobile transmission, and I don’t believe that is a good analogy.

    It is difficult to beat electric traction, because even at zero RPM, an electric motor can produce 100% of its designed torque. An internal combustion engine, must have revolutions to generate torque. Check the owners’ manual of your car; torque in ft-lbs is given at a certain rpm.

    One of the principal reasons for gearing the traction motor to the axle is to protect the motor. The established gear ratios are in placed to keep the motor from rotating too fast and becoming a bird’s nest of wiring, and at the other end of the spectrum, rotating too slowly at full throttle so that the motor over heats. Too be sure, the gear ratio will affect performance in terms of acceleration rates and the TE vs Speed Curve.

    I saw this analogy once that attempts to show how locomotives of different horsepower and with different gear ratios can work in the same consist. I can’t remember the source, but it went something like this. A man (high horsepower, high speed) attempts to pull a loaded wagon, but lacks strength to move it. He enlists the aid of his 10 year-old son (low horsepower, low speed). The two of them, pulling at the maximum effort, are able to move the wagon easily, and as long as their speed stays lower than the speed at which the boy would stumble (gear ratio), everything is fine. It’s not a perfect analogy, but it gives a notion of how the Frisco could operate a SD-45/F-7B/SD-45 consist or an E-8/F-7B/E-8 consist without problems. With regard to your query about the Type-B, road truck equipped GP-35’s operating with other EMD units, the answer is, it wouldn’t be a problem. Also remember that the FA’s/FB’s (the source of the Type-B trucks) operated in the same consists with the EMD F-units and GP-7’s.

    Last edited: Feb 12, 2018
  3. meteor910

    meteor910 2009 Engineer of the Year Staff Member Supporter

    Karl's excellent explanation and graph also shows why you should never get into a drag race with a Tesla. You will lose.

    gjslsffan and modeltruckshop like this.
  4. modeltruckshop

    modeltruckshop Member Supporter

    Thanks for the explanation Karl. Well done.
    gjslsffan likes this.
  5. Ozarktraveler

    Ozarktraveler Member Supporter

    "Itis difficult to beat electric traction, because even at zero RPM, an electric motor can produce 100% of its designed torque." For true...

    That sounded like Naval Basic Electronics and Electricity school, electric motors class. :)
  6. adams

    adams QLA-QSF

    Thanks, Karl! So I guess using your analogy, the son’s shorter legs would be running faster than the man’s—-so that would mean at a given speed, the lower-geared unit’s traction motors will be turning higher rpms, correct? If so, assuming the same amperage is being applied to all motors in all units, does power drop a bit in the low-gear unit as it is receiving the same amps, but is forced to spin faster? (In other words, can the son not apply all his optimum power while keeping up with the man?). Hope I’m not being tedious with my mental gymnastics!
    Last edited: Feb 12, 2018
  7. gjslsffan

    gjslsffan Staff Member Staff Member Supporter

    I had been thinking about this so I digs up some old manuals of mine, also from a friend's house today. These gear ratios can get into a quagmire of many sorts.
    Its all based on the amount of turns the pinion gear rotates to turn the bull gear (driven axle/wheel) once. So consider 62:15 is really a basic equation of 62/15= 4.13333 or reduced 4 turns of the pinion to one rotation of the bull gear, a 74/18= 4.11111, simplified is same same. So really not much difference when it come right down to it. But consider a 74:18 will have a finer gear tooth and more teeth engaged in the process, thereby making a stronger gear mesh between the pinion and bull gears, kinda like comparing a fine tooth threaded bolt to a standard thread bolt. Karl's explanation of different gear ratios and how they work together is great, he puts it in terms easily understood. I don't know if this was an Alco thing or an after thought.

    Many EMD's as these are the stuff I am familiar with, were 61:16, which is a higher gear ratio with a 3.8 rotation of the pinion to one on the bull gear is clearly a higher gear ratio that was used by many RR's, but when you do this, you need to bear in mind that you are actually reducing your locomotive tonnage rating in a hard pull, by reducing the short time rating on the units. Meaning the higher the gear ratio the more amps, or heat generated on the traction motor to turn it at the same speed. Which all again goes into what Karl was saying about different people working together. A DC motor in the short time rating too long, can burn brushes or segments on the commutator, which will give you problems, I have even seen them catch fire. Later DC units, have processors that will reduce the amperage to the DC traction motors to keep from burning themselves up. Basically turning your SD60 into an SD40 or GP40 if they get hot enough.

    AC traction motors change all this as heat or Amps into a motor does not directly relate to heat generated in a given traction motor in the same consist. Neither does maximum axial rotation or RPM as it relates to "Birds Nesting". Which explains why EMD AC traction motors will often have a 85:16 or 85/16= 5.3 rotations of the pinion to bull gear ratio, again more teeth engaged making a stronger gear to gear engagement, also explains why AC's are so powerful at lower speeds, and why they use 44/45" wheels for more wheel to rail contact, more adhesion and more tractive effort.

    Anyway maybe a bit more info than you wanted.
  8. adams

    adams QLA-QSF

    Not at all! Thanks for the input. The more I read, my head will eventually wrap around the concept. Let me ask a couple of clarifying questions, if you’ll indulge me...
    1). At a given run setting (notch) in the controlling unit of a consist, will that apply the same amperage in all units?
    2). At a given amp draw (run setting) will a faster-turning traction motor produce less force than a slower one? (I think you probably see what I’m getting at, as a low-geared motor will be turning more rpms at a given speed of the consist)
    Again, thanks for the conversation
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  9. modeltruckshop

    modeltruckshop Member Supporter

    Tom, thanks for that. I also realize how dumb I am now though. I understand truck axle gears but this is outta my league.
  10. gjslsffan

    gjslsffan Staff Member Staff Member Supporter

    There are so many variables involved in this wrinkle. let's say say in theory yes, they should put out similar amperage. When the Engineer calls for power the same throttle setting is propagated through out the consist (were talking about all units on the head end, and all on-line). It all depends on what kind of amperage that unit is designed to put out at that notch. If the load regulator decides the engine and supporting cast is up to putting the amps out, then yes, that unit will put out similar amperage. But you gotta understand that this all depends on the tonnage, grade, speed, and a host of other conditions that can have an effect on all of this. When you are starting a heavy train out even on level grade the amperage can get pretty high even at lower throttle settings, and the amperage will generally drop as speed increases. Adhesion has a great deal do do with all this, On wet rail, I have been on power that had wheel slip and amperage loss at 40 mph. The tonnage involved is hard to grasp unless you have lived it sorta speak. Just for example I was on a heavy unit sand train on a ruling 2 1/2% grade with 3 AC units on the HE and 2 AC units DP'd on the rear, the screens showed they were all pretty close in amperage output until the lead unit, which in this case was one of those miserable GE C4's, yea its AC but only 4 of the 6 axles are powered. We would hit a rail lubricator and the amperage on that lead unit dropped substantially, so much so that those EMD ACE's behind it, kicked that GE in the behind, pushed it and pulled the train until that C4 decided it was time to go to back to work again. We would loose 2-3 mph every time then eventually regain the speed till the next lubricator, 2-3 mph does not sound like much, unless in our case we were doing 8-9 mph at best. GE AC's that have all 6 axles powered are good pullers too. But you just cant put all that amperage to the rail in 4 powered axles in those conditions, and speeds. I hope you understand what I am trying to say here. Its not all that exact sometimes, DC power as well as AC power even in the same consist, will do all they can generally, until their limitations are met.
    We could go on and on but, I think you can understand what I am saying.

    2) All depends on the "given speed" and grades, at 40 mph on river grades there wont be much difference, at 10 mph in mountain grade territory, that higher geared motor will want more amperage to maintain the speed. It will still be pulling all it can until its limits are met. I'm sure I left stuff out on this reply, it is just hard to answer in specifics when there so many nonspecifics involved.
    Joe Lovett likes this.
  11. adams

    adams QLA-QSF

    Thanks for the insight!
    Joe Lovett likes this.

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