Uh, the fan wasn’t for smoke.
It’s mounted directly above the motor (in the FIREbox), blowing DOWN onto the motor.
Unfortunately, it affects smoke (mounted in the SMOKEbox), and folks turn the fan around to “fix” that little oversight…and obviate the cooling effect of the fan on the motor.
Now are you a tad more confused?
How about trying to “prove” your error isn’t a year later?
Ah.
Now, how to deal with the 28:1 reported for the next loco…
In engineering practice, one would need to take many variables into account to arrive at a final solution. Variables are a) power available, b) final drive gear ratio, c) drive wheel diameter, d) expected draw load and e) anticipated top speed.
Everyone knows that general practice is that a dump truck will have a bigger motor than a family car, will have a lower top speed and a different final drive ratio. Most gearboxes have a top gear with a 1:1 ratio, therefore, the final drive ratio is the variable that effects top speed given that we know the motor maximum speed. If a dump truck had a final drive ratio the same as a family car, then its anticipated load would be considerably reduced, plus the additional weight of the truck would strain the motor, effectively reducing the expected top speed.
A manufacturer would calculate all the variables and arrive at a gear ratio situation that would be engineering ‘best practice’ to lessen the load factors on both the drivetrain and the motor. Now, it would appear that Stanley is making statements contrary to known engineering principles, in that one, the gear ratio is relatively unimportant as the overriding factor is top speed and secondly, seemingly, an unbelievable statement that a smaller flywheel is conducive to smoother running.
To me it seems that damage control is in place, with constant references to electronics being more important to reliable running, than a gearbox ratio. One does not compensate for an incorrect gear ratio by providing a bigger motor and then overloading the motor to the point that a cooling fan is required. Pitman have been making motors for generations and yet do they advise or even provide a cooling fan at point of manufacture? It seems that all these wonderful electronics have a limit and that is the actual mechanics in the design. A properly engineered gearbox ratio would alleviate many of the ‘electronic’ problems experienced.
Way to go Tim!!!
You too will be on the “persona non grata” list soon.
Tony,
I am not placing myself on one side of the fence, or the other. I am simply stating what has been the generally acceptable rationale that has sustained our hobby for a hundred years. It seems that the wheel is being reinvented and to compensate for not being round in shape, complicated electronics are utilised to ‘smooth out the bumps’.
The K-27 had a nickname, 'mudhen'. It is not because it squawked like a duck, but because it constantly liked to play in the mud beside the railroad. Derailments were common and thus maximum speed was reduced by decree. Seeing top speed as the overriding rationale when designing a drive train, particularly when one is talking about the 'K' is pointless. The loco would rarely have been driven at maximum speed, considering the state of disrepair of the rail and subsequent derailments.Tim Brien said:That looks like a backhanded way of taking a position on the subject to me. ;)
Tony, I am not placing myself on one side of the fence, or the other. I am simply stating what has been the generally acceptable rationale that has sustained our hobby for a hundred years. It seems that the wheel is being reinvented and to compensate for not being round in shape, complicated electronics are utilised to 'smooth out the bumps'..
Tim Brien said:Our points precisely. These are supposed to be scale models with some allowance given to driver dimensions to get them to stay on our #1 gauge track. It does not mean the mechanics should be dictated by those that want to play slot trains. The second batch of K-27's are fantastic locos that would have been Oh! So! much better with the correct ratios.
Tony, The K-27 had a nickname, 'mudhen'. It is not because it squawked like a duck, but because it constantly liked to play in the mud beside the railroad. Derailments were common and thus maximum speed was reduced by decree. Seeing top speed as the overriding rationale when designing a drive train, particularly when one is talking about the 'K' is pointless. The loco would rarely have been driven at maximum speed, considering the state of disrepair of the rail and subsequent derailments.
The Accucraft K-27 has suitably low gearing resulting in absolutely smooth low speeds.
I never hear complaints about their ratios being too low and restricting the top speeds.
Thank you.
TonyWalsham said:Tony, most likely the fan is required because the motor has too high power for a small enclosure in which it is contained - I have never seen the K-27 from inside but perhaps someone can provide this info, whether the Bachmann's K has a fully enclosed motor. If so, and if the motor power is greater than 25 Watt (Barry Olsen - could you please confirm?) there is a need for a fan (irrespective of the gear ratio). In fact the dissipated power is not a function of the gear ratio at all - the available momentum is (in other words torque on the drivers and the related tractive effort). So in plain language, the gear ratio determines how much you can pull (provided your locomotive is heavy enough and the K is not for its motor) while the dissipated heat is proportional to how much you are actually pulling (through square of the current drawn). In the limit of stalling, the motor stands still and draws max current and dissipates precisely the same amount of heat independently of the gear ratio. Best wishes from Tokyo, Zubi PS how smooth the motor operates depends to a great degree on the type of the motor (how many poles and their geometry, etc) - doubling gear ratio mainly halves the period of the fluctuations, similar to doubling the pole number - the momentum/torque fluctuations are still there, but twice more frequent.
Zubi. If 1:14.5 was such an ideal ratio and was such an efficient low power draw set up, why did Bachmann find it necessary to add a fan to keep the motor cool? The 1:14.5 ratio places an unneccessarily excessive load on both the motor and the control system. This creates heat which would not be evident with a lower ratio such as the proposed 1:29 ratio. The biggest benefit to the operator of a lower ratio, will be much smoother starts. Top speed will be reduced but that is easily overcome by increasing the voltage of the batteries if necessary. Somehow I doubt it will be necessary as the top speed will still be plenty fast enough on 14.4 volts.
WoW!!!
That beats my bid. 
Zubi,
as a layman, I have a little problem with your science as it relates to reality. You are saying that regardless of the gear ratio chosen, the motor will still run hot and requires a fan to aid in cooling.
I believe that an electric motor has its maximum current draw at the point of stalling. It is at this point that maximum heat is generated - torque equates to current draw, which is directly related to the amount of heat generated. With a numerically higher gear ratio (lower numerically), then as the locomotive overcomes its 'state of rest', more power is required to move it (less torque multiplication, thus more power required). If a lower gear ratio (higher numerically) is used, then the torque multiplication available by the lower gear ratio (say 30:1) enables the motor to better apply its torque and thus reduce the amount of current draw and subsequent heat generation. Your statements totally refute my beliefs.
If a sufficiently powerful electric motor were available, then, in reality, no gearbox reduction is required and a direct drive would be possible. However, this is not practical, nor desired in the model world, as the heat generated would be immense and the current draw considerable. The gearbox has a major part to play in converting the torque, in the motor, to the rails and yet still be practical and functional.Boy.
Accucraft better hire Zubi right quick!
All those Pittman motors need fans now.
Horse Poop.
Tim Brien said:
Zubi, as a layman, I have a little problem with your science as it relates to reality. You are saying that regardless of the gear ratio chosen, the motor will still run hot and requires a fan to aid in cooling.I believe that an electric motor has its maximum current draw at the point of stalling. It is at this point that maximum heat is generated - torque equates to current draw, which is directly related to the amount of heat generated. With a numerically higher gear ratio (lower numerically), then as the locomotive overcomes its 'state of rest', more power is required to move it (less torque multiplication, thus more power required). If a lower gear ratio (higher numerically) is used, then the torque multiplication available by the lower gear ratio (say 30:1) enables the motor to better apply its torque and thus reduce the amount of current draw and subsequent heat generation. Your statements totally refute my beliefs.</blockquote>Tim, thank you for the comment. There is no problem here since your statement agrees in full 100% with what I said in my previous posting.
In the limit of stalling, the torque available on the drivers depends on the gear ratio. However, the actual heat dissipation only depends (quadratically) on the current drawn - the gear ratio has nothing to do with the value of the current drawn at stall and, therefore, has no influence on the power dissipated at stall. This is all elementary physics (high school level) and while I perfectly understand that this requires some explanation to laymen, it should be perfectly accessible to people who consider themselves experts in powering electric locomotives;-)))Tim Brien said:As in many other fields, also in this field of large scale electric locomotives one need to optimise certain parameters. We use gearboxes in order to increase torque and limit the max rpm of the motors, mainly. Everyone agrees on this. You can use the 9000 Pittman motor, with a 1:1 drive but your tractive effort on 1:20.3 scale drivers will be only 1.18kg which is still a decent value. However, your speed at 19V would be near the speed of sound (scale;-) and equal to 1172.32km/h The speed of sound in dry air at 20%C is 1235 km/h so you would go supersonic at 20V and above;-)))... Not everyone wants their K to travel at the speed of sound and therefore an rpm reducing gear box is required.
If a sufficiently powerful electric motor were available, then, in reality, no gearbox reduction is required and a direct drive would be possible. However, this is not practical, nor desired in the model world, as the heat generated would be immense and the current draw considerable. The gearbox has a major part to play in converting the torque, in the motor, to the rails and yet still be practical and functional.Having said this, if the weight of the K-27 engine is near say 7kg any gear ratio from say 7.25:1 to 29:1 would do. The engine could still pull the same, with any gear ratio, before it slipped. But you could only operate the engine prototypically within say 0-5Volt for the lowest ratio. This is not practical, if your motor is capable of working up to 24V so a double ratio makes a perfect sense even if you cannot use half of the available torque. The additional benefit is a better dynamical response because of a higher momentum at a larger rpm of the motor which helps to “smooth out” the movement - this is not equivalent to the higher frequency of momentum fluctuations which I discussed in the context of the point which Tony Walsham made, but perhaps this is what he meant. Would a quadruple gear ratio be better? Yes, marginally (smoother, higher voltage range thus lower current, but at least 75% unused torque), however, this is not the point here in this thread.
I am not suggesting any particular gear ratio as an optimum - everyone can choose their own and be happy with it. However the laws of physics are not a matter of personal preference and what I have done in my postings in this thread was demonstrating that when you use these to calculate precise values, they perfectly support the point which Mr Stan Ames made in his posting cited at the opening of this thread. Through the remainder of this thread he’s been referred to as a confused, clueless cretin, etc, etc, for stating what can be proven to be true by a high school student. I thought that enough is enough - in my opinion the “experts” who have engaged themselves in bashing him without even understanding his statement on this particular issue have discredited themselves as professionals.
Best wishes from Tokyo, Zubi
Curmudgeon said:
Boy. Accucraft better hire Zubi right quick! All those Pittman motors need fans now.Horse Poop.
Accucraft motors sit about like Bochman’s do.
Bochman’s are mounted to a metal gearbox, held with a strap to a (are you ready for this?) METAL frame.
The firebox is OPEN.
I know why there is a fan, as I was told.
You haven’t a clue.
I also know why there is a flywheel and external thrust bearings on both ends of the motor, as I was told.
You, once again, have no idea.
I also know why the unit as delivered is 14.5:1 gear ratio, as I was told, and you are just trying to help Stanley “prove” it’s right.
You haven’t even seen one of these, much less run one or taken it apart.
I am as of right now, this minute, 2200 local, done dealing with you and your support of a world-class moron.
Bye!
Zubi,
you are correct that at the exact moment of the drive motor stalling, then the gear ratio chosen is irrelevant. However, what you have conveniently overlooked is that a heavy locomotive will reach the ‘exact moment of stalling’, more readily with a higher (lower numerically) gear ratio than a loco fitted with a more practical low ratio (high numerically) gearbox. Gearboxes are not just output drive revolution limiters, by reducing the input drive speed, but also torque multipliers, by virtue of the gear reduction. The idea of increased torque is to make the life of the input drive motor more ‘comfortable’.
Once the loco is in motion and travelling at optimum speed, then a higher gear ratio will aid the motor. However, to reach the optimum speed, the motor must overcome the lack of torque available from rest. A low ratio gearbox would be advantageous in this situation. Until we have dual range gearboxes then I will stick with the premise that a low ratio gearbox is preferable in terms of an operator who is going to be operating his 'K' in prototypical fashion. Not everyone believes that a locomotive is a Formula 1 racecar and thus top end speed is relatively unimportant.Zubi,
There are no values given in Watts on the Pittman data sheets. I suspect that the watt values are a combination of other values calculated to produce the watt values. If you an direct me to the values needed to produce the elusive watts, I’ll try and find them for you.
Barry - BBT
Tim, thanks for the comments.
Tim Brien said:Tim, this is not entirely correct. There is no such thing as rest for electric motor unless it is not powered. If they are powered and not turning they are stalled - the current will be roughly proportional to the voltage applied. Thus, electric motors have torque available "at rest" - or rather while stalled, due to the fact that they are driven by a magnetic field which works regardless of whether they are in motion or stalled. In fact, as you wrote earlier, maximum current (voltage dependent) will be drawn when they stall.
However, to reach the optimum speed, the motor must overcome the lack of torque available from rest.
Tim Brien said:I completely agree with you. The motor will overcome the point of stalling easier with a higher numerical gear ratio in terms of the torque required on the shaft of the motor. But please recall what is the original starting point of this thread - the question whether the K equipped with the Pittman 9000 motor and 1:14.5 gear ratio can actually use the torque provided by the motor. My conclusion supported by calculations is that the K will not be able to utilise the torque available on the drivers. Other than hand-waving arguments and offensive language I have not seen any proof to the contrary.
Zubi, you are correct that at the exact moment of the drive motor stalling, then the gear ratio chosen is irrelevant. However, what you have conveniently overlooked is that a heavy locomotive will reach the 'exact moment of stalling', more readily with a higher (lower numerically) gear ratio than a loco fitted with a more practical low ratio (high numerically) gearbox. Gearboxes are not just output drive revolution limiters, by reducing the input drive speed, but also torque multipliers, by virtue of the gear reduction. The idea of increased torque is to make the life of the input drive motor more 'comfortable'.
The question which you are asking now is different. We can approach this different question from two ways, one is at the same voltage for both gear ratios, the other is the same acceleration (which will require higher voltage for gear ratio higher numerically) For both scenarios, please remember that the energy required to overcome the stalling force and move a certain - even microscopic distance (work done) will be the same for any gear ratio. Due to the law of the conservation of energy (or the first law of thermodynamics if you will) this will be equal to the difference between the input energy (from the transformer) and the dissipated heat (in the motor). The dissipated heat is proportional to the squared current (or the current times voltage drop on the motor). Now, in the same voltage scenario the motor will require less current and will therefore dissipate less heat with the numerically higher gear ratio (but we will move slower). In the same acceleration scenario, the voltage required to achieve this will have to be higher for the higher numerically gear ratio and the heat dissipation will be the same for both gear ratios.
Tim Brien said:I am not saying that the higher numerically gear ratio is worse!! Of course there are many advantages of using a higher numerically gear ratio, together with the entire voltage range for the motor. Please check this discussion for some arguments concerning this point: http://www.largescalecentral.com/LSCForums/viewtopic.php?id=10047&p=5 The only disadvantages I can think of is that the noise level of the motor at full rpm may be high and of course if you want to use battery power, requirements grow with higher voltage range - I said that above. But this is a different issue than the discussion of whether the locomotive can use the available torque and this is the only point which I am aiming to discuss here. Best wishes, Zubi
A low ratio gearbox would be advantageous in this situation. Until we have dual range gearboxes then I will stick with the premise that a low ratio gearbox is preferable in terms of an operator who is going to be operating his 'K' in prototypical fashion. Not everyone believes that a locomotive is a Formula 1 racecar and thus top end speed is relatively unimportant.
Ah Curmee, we all make mistakes don’t we;-)))
You had one chance in this thread to admit that
he is correct this time but you missed it;-(( tsk tsk…
Let’s hope you will get another one! Good night, Zubi
Curmudgeon said:
I am as of right now, this minute, 2200 local, done dealing with you and your support of a world-class moron.Bye!
TOC is no lnoger on this thread! Interesting! OK, I won a K-27 of Bachmann manufacture, #455 with the BIG WIDE Snow Plow, which has been replaced! I will need to trim the front and rear steps to clear stuff on the ROW. As to not running the K, I 'm not at this time due as much to SIZE as to power, it will run thru batteries (4500Mh) rather quickly which says that the power draw is high! When Mr. BBT gets his grew box perfected and I can afford one I’ll be installing one. I prefer lower speed and better control. If you all want HIGH Speed please go but a Bullet Train!
Paul
Zubi,
a very thorough response, which in my mind proves just one thing - a layman with little direct knowledge, but a lot of experience, is as knowledgable in a particular situation as a college professor. I know my basic laws, but I also know what I want from a model. Certainly, the assumption is that the higher gear ratio on the production ‘K’ is able to use the power of the Pittman motor, but at what cost? You mention the noise of a motor at maximum rpm as a criticism and yet, most operators would never attain maximum rpm, whatever gear ratio was used.
The 'opponents' of the Stanley Ames camp are not boggle-eyed youngsters, bent on wringing every last drop of speed out of their locomotive, but experienced model railroaders, who want a scale model to behave as a scale model. I am not criticising Stanley (or yourself), but in his defense, he is more interested with attaining the prototypical top speed of the loco, at 18 volts and baffling us with electronics than with providing us with a locomotive that performs as brilliantly as it looks. Many do not use 18 volts as their operating voltage, so how valid is attaining a maximum speed if the fixed input criteria is actually a variable?A small additional point, some of the assumptions were made because - and I am trying to paraphrase this right - because “I” have observed the K’s wheels spinning with the current gear ratio, thus you do not need any “more” gearing, it’s already at it’s limit now, so what’s wrong with the gearing, it’s “enough”.
Recently a young person did a school project and got results that many experienced modelers already knew, different rail materials and conditions provide different coefficients of friction.
TOC’s aluminum rail is WAY more “grabby” than my slick Aristo SS, and more than oxidized brass. and a lot more than clean brass.
Now, I know that Stan has hybrid drive, but I believe his track is more clean than dirty. So, Stan has locos slipping a lot earlier than TOC will.
In fact, it is definitely not hard to imagine that Stan’s locos are slipping under the same load that TOC’s would not slip and lug down the motor and gear train.
Based on that, it’s not a “done deal” that the K’s gearing is “low enough” in my book.
Add to this one final small point… your greatest traction is JUST BEFORE the wheels break loose and slip… (difference between static and kinetic friction for you physics guys) so you want to get all the “smooth power” up until that point in your loco to maximize pulling power. This seems to speak of lower gear ratios and smoother power transistions, not a BEMF circuit trying to compensate load and power at EVERY commutator segment.
I am a DCC guy, and I have BEMF decoders. I follow the old adage: make your loco run as well as possible on straight DC, electronics cannot turn a poor running loco into a great one.
Regards, Greg
Greg, can I use this as my new sig line if I identify you as the author?
Quote:
. . I follow the old adage: make your loco run as well as possible on straight DC, electronics cannot turn a poor running loco into a great one.Regards, Greg
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