Hello All. I was reading that the Frisco GP35s that had the AAR Type B trucks had slightly different gearing than the EMD trucks and traction motors. How would that affect a multiple unit lash up with other EMDs? Would the GP35s wheels want to turn at a different rate with the same current draw all the locomotives were getting? I know all sorts of locomotives with different gearing have been lashed up together, but I guess I just do not understand the specifics. Thanks, Chris
I believe that we a prone to equate the gearing of diesel locomotive to an automobile transmission, and I do not 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 foot pounds 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 place 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 tractive effort verses 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 cannot 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 is not a perfect analogy, but it gives a notion of how the Frisco could operate a SD45/F7B/SD45 consist or an E8A/F7B/E8A consist without problems. With regard to your query about the AAR Type-B road truck equipped GP35s operating with other EMD units, the answer is, it would not be a problem. Also remember that the FA-1s/FB-1s, the source of the AAR Type-B trucks, operated in the same consists with the EMD F-units and GP7s.
Karl's excellent explanation and graph also shows why you should never get into a drag race with a Tesla. You will lose. K
"It is difficult to beat electric traction, because even at zero RPM, an electric motor can produce 100% of its designed torque." So true. That sounded like Naval Basic Electronics and Electricity school, electric motors class.
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!
I had been thinking about this so I dug up some old manuals of mine, also from a friend's house today. These gear ratios can get into a quagmire of many sorts. It is all based on the amount of turns the pinion gear rotates to turn the bull gear on the drive 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 gear ratio of 74/18 = 4.11111. Simplified it is same same. So really not much difference when it comes right down to it. But consider that a 74:18 gear ratio 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, 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 do not know if this was an Alco thing or an after thought. Many EMD locomotives traction motors, as these are the stuff I am familiar with, had a gear ratio of 61:16. This is a higher gear ratio with a 3.8 rotation of the pinion to one on the bull gear. It is clearly a higher gear ratio that was used by many railroads 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. This means 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 electronic 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 gear ratio of 85:16 or 85/16 = 5.3 rotations of the pinion to bull gear. Again, more teeth engaged makes a stronger gear to gear engagement. This also explains why AC powered locomotives are so powerful at lower speeds, and why they use 44" or 45" wheels for more wheel to rail contact. This results in more adhesion and therefore more tractive effort. Anyway, maybe a bit more information than you wanted.
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 will indulge me. 1) At a given notch run setting in the controlling unit of a consist, will that apply the same amperage in all units? 2) At a given amp draw or run setting will a faster-turning traction motor produce less force than a slower one? I think you probably see what I am getting at, as a low-geared motor will be turning more rpms at a given speed of the consist. Again, thanks for the conversation.
Tom, Thanks for that. I also realize how dumb I am now though. I understand truck axle gears but this is out of my league.
1) There are so many variables involved in this wrinkle. Let us say say in theory yes, they should put out similar amperage. When the engineer calls for power, the same throttle setting is propagated throughout the consist. We are talking about all units on the head end, and all are 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 have to 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, so to 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 headend and 2 AC distributed power units on the rear. The screens showed they were all pretty close in amperage output until the lead unit wheels slipped. In this case the lead unit was one of those miserable GE C4s. Yea, it is an AC unit, but with only 4 of the 6 axles are powered. When we hit a rail lubricator and the amperage on that lead unit dropped substantially. So much so that those EMD ACEs 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 lose 2-3 mph every time then eventually regain the speed till the next lubricator Two to three 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 cannot 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. It is 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 will not 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 am sure I left stuff out on this reply. It is just hard to answer in specifics when there so many non-specific variables involved.
