But, but, but Cale, remember: these are only toys, most of what ails the world today can be fixed with some electronic gizmos, water will flow up hill if given half a chance and given enough time to evolve … pigs will fly.
(http://www.clicksmilies.com/s0105/teufel/devil-smiley-023.gif)
Comme ca?
(http://static.flickr.com/46/143483048_dbfd053984_o.jpg)
I’d bet on porcine aviation before I would a Bachmann locomotive that doesn’t have to be “fixed” to run as good as it looks, at least under the current ROE. Matthew (OV)
I must say that this is beyond belief, dear Highly Esteemed Contributors to this thread;-) You do not seem to have the slightest clue of what you are talking about! Electric (and steam) motors provide torque even when stalled. Mr Barry Olsen provided the figure for this characteristic of the Pittman 9000 motor - 41.3 lbin which translates to 598lbin when a 14.5:1 gear ratio is used. The resultant maximum tractive effort on a 40inch driver scaled down by 20.3 is 603.7 lb (275.5kg). You can pull a few adults using this kind of torque! Of course this would have been doubled if a 29:1 gear ratio were used (that is the tractive effort would become 1207.4 lb) but both values are way above what a plastic G-scale locomotive can handle!!! In other words, the available torque is so huge that the only decisive factor is the locomotive weight - the locomotive weight would have to be greater than the tractive effort in order to prevent slipping! Obviously, this is physically impossible and the plastic K-27 is two orders of magnitude lighter. This is also why Mr Ames is perfectly correct in stating that the weight of the locomotive is the decisive factor in this case and not the gear ratio! One can add weight to the locomotive, but this will be quickly limited by the strength of the mechanical components to handle the torque available and will not reach anywhere near the maximum tractive effort provided by the Pittman 9000 motor!! I am flabbergasted to see that people who claim to be experts do not appear to understand such elementary concepts. While Mr Ames is - strictly speaking - not correct about the precise values of the maximum speed of the engine vs voltage/rpm of the 9000 Pittman motor - which I discussed in another thread http://www.largescalecentral.com/LSCForums/viewtopic.php?id=10047&p=5 he is correct about the torque vs gear ratio issue. The maximum speed is a minor issue and in fact there are more pros than cons of operation in a limited range of the motor voltage available! Firstly, maximum rpm can easily be altered by electronics or by hand - this is hardly a problem in real life. Furthermore, if the motor has enough torque it is actually advantageous to operate it at a reduced rpm - the motor is much less noisy then. Finally, smaller voltage range makes powering with batteries easier. Back to this thread - Mr Ames is correct here so please get off his case! Best wishes from Tokyo, Zubi
So why are Bachmann issuing the Mallet with 28:1 gear ratios??
Hi Tony, this is difficult to answer as I do not know which motors have been used on the Mallet. If, as rumor has it, the motors are Pittman 8000 model, their rpm is 65% higher than that of the 9000 motor. This requires reduction and a factor 2 is quite applicable in this case as 9000 produces quite high rpm in the first place. http://www.largescalecentral.com/LSCForums/viewtopic.php?id=10047&p=5 Best, Zubi
Zbigniew Struzik said:That says it all Zubi, that says it all.
Hi Tony, this is difficult to answer as I do not know...... Best, Zubi
Do you know when you load that motor down with that gear ratio what it does to the current?
Oh, wait, you don’t care, right?
Well, sorry, bucko, I do.
You know what it does to starting characteristics with a 14.5:1 ratio WITHOUT electronics to “compensate”?
I do.
Tested them on straight DC and PW control.
I KNOW what it does.
Hi Curmee, if you do know, please confirm whether it is 8000 or 9000 series;-) This is all we need to know as I have just explained above! If you have any additional information, please provide it in a comprehensible way - there is no need to try to confuse the readers of this thread more than they have been so far!!! If you find any inaccuracy in what I write please feel free to point it out - with all the necessary calculations. If you do not, please refrain from generating noise and dissipating heat;-)))! Best, Zubi
Curmudgeon said:Zbigniew Struzik said:That says it all Zubi, that says it all.
Hi Tony, this is difficult to answer as I do not know...... Best, ZubiDo you know when you load that motor down with that gear ratio what it does to the current?
Oh, wait, you don’t care, right?
Well, sorry, bucko, I do.You know what it does to starting characteristics with a 14.5:1 ratio WITHOUT electronics to “compensate”?
I do.
Tested them on straight DC and PW control.
I KNOW what it does.
The only “leaked” information is that it is a custom-wound 24V motor (want to believe that? Their on-line catalog STILL shows the K as having a 24V motor).
“custom-built 24 volt Pittman motor with double shafted brass machined flywheel”
http://www.bachmanntrains.com/home-usa/products.php?act=viewProd&productId=2031
The video cals the artic motors as custom-wound 24V motors.
Is this more obfuscation?
Rumour is they are NOT Pittmans, but, that’s a rumour.
Zubi, the K draws over 5 amps at full slip.
The motor is rated for 1.7A continuous.
The gears are too tall.
I’ve tested it, I know what it does.
Even the Obfuscator himself shows a video of 30 cars on a 4%, except, listen carefully, and you will hear the REAR END PUSHER start up, then the MID-TRAIN HELPER start up, THEN the lead loco starts.
You have a large enough power district, okay, but I know with 20 cars on a 13’6" diameter 4% grade, one engine is over three amps.
Yet, with 29.9:1 and a Pittman, I know what a 4-6-0 or 2-8-0, even an outside-frame 2-8-0 will do.
I should add, those current draw figures were obtained after the review was written, on the old aluminum track out on the railroad, not the shiny brass stuff in the review area with track power.
Almost 3X more current required to go to full slip.
All the Pittman motored 4-6-0’s, inside and outside framed 2-8-0’s are tested on the same aluminun trackwork.
Zbigniew,
IMPORTANT>…the torque figure is 41.3 oz.in (Inch ounces). I know these by heart, I hope I didn’t say pound inches.
ZS, my apologies I did say inch pounds. I went back and checked my post. Sorry to have misled anyone.
Barry - BBT
Barry, thanks! This brings us closer to realistic figures;-)… I could not quite believe what I saw after calculating. I mean, you could almost pull a real train with this kind of torque;-)) and require current in excess of 100A;-))) at 20volt levels… Well, taking into account the true torque of the Pittman 9000, the correct tractive effort is 37.7 lb (17.1kg) with the 14.5:1 gear ratio. This figure would be doubled at 29:1 ratio. While not as insanely overpowered as it seemed when I did the initial calculation, the locomotive would have to weigh at least this much in order to utilise this kind of tractive effort. Clearly, the argument remains as presented in my initial posting in this thread. in spite of the incorrect data used there - I do not know the precise weight of the Bachmann’s K-27, but I do not think that it is anywhere near 17.1kg - more likely three or four times lighter… As usual, the readers are welcome to draw their conclusions!! Best wishes from Tokyo, Zubi
Barry Olsen said:
Zbigniew,IMPORTANT>…the torgue figure is 41.3 oz.in (Inch ounces). I know these by heart, I hope I didn’t say pound inches.
ZS, my apologies I did say inch pounds. I went back and checked my post. Sorry to have misled anyone.
Barry - BBT
According to the responses herein; to the original posted question…some of you believe that Gearing matters, and others do not…is that a correct assumption?
Stanley wants to change the history of model railroading, and all the work done by everyone to this point in the hobby.
Zubi apparently has drunk the Kool-Aid.
Me?
I just parked the K and it will stay parked until I get some new gears in it.
It would be interesting to hear from people who actually own this engine besides Mr. Curmudgeon and hear what they think of the performance characteristics of the engine. I’m yet to hear anyone else’s opinion of how it performs.
P.S. Please save us the torture of the “Marvin” crap and all of the ranting and raving about my sanity that go with it- it’s gotten quite old and worn at this point!
The thread had to continue until we dragged you into it.
Done now!
In my little story, I neglected to make the point of how the “correct” gear ratio was determined. It wasn’t done by numbers exclusively. What was desired was the best slow movement possible, superior pulling power and lastly reasonable speed. We started with extremes a 20T and a 12T spur gear. As I mentioned the 12T was too slow.
I produced the 20T version for a while, but it lacked the low speed power one needs to negotiate some grades (Dave’s 80Ft 4% comes to mind). So the compromise was tried the 16T and it gave me what I wanted and got Dave’s approval as well (not always easy to do). I have a U-25 with a double shaft Pittman in each truck, it is a healthy puller, running four double thread worms on 30T gears, that is 15:1. But the wheels are just over an inch in diameter; smaller wheels give a greater mechanical advantage.
Barry - BBT
Cale Nelson said:Cale, no it is not correct. Of course everyone knows that gearing matters. Mr Stan Ames says this in the first sentence of his note which you cite!! I calculated tractive force for both gear ratios and you can see there that tractive force is doubled when the gearing ratio is twice as large. So we all agree that gearing matters. The crux is that even with the 1:14.5 gearing the torque on the drivers is so large that it is not possible to convert it to the tractive force if the engine (without the tender) weighs less than 17kg!! If the gearing were 1:29 the engine would have to weigh 34kg. This is not realistic for a G scale engine, especially a plastic one! Please note that the same forces would have to be tranfered by the side rods - I believe they are metal but most likely not designed to carry such forces. The essence of my calculation is that with the 1:14.5 gearing the K-27 the tractive effort of the K-27 is only limited by the weight of the engine and this is exactly what Stan Ames's original statement says. Best wishes from Tokyo, Zubi
According to the responses herein; to the original posted question....some of you believe that Gearing matters, and others do not...is that a correct assumption?
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.
Ah, don’t you love it when something shows up in the “inbox” that applies so well?
“Every great mistake has a halfway moment, a split second when it can be recalled and perhaps remedied.”
Pearl S. Buck
TonyWalsham said:It has been quite entertaining to watch the Woebeuntobachmann tribe feast upon their young. One tribe member bemoans the lack of pre-production testing and the rest seem to salute that proposition with a stomp around the campfire.
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?
So tell me, the current theory is that Bachmann was clueless when they choose the gearing, but then had the epiphany to install a motor cooling fan for a problem they didn’t know existed?
Before that they were clueless for installing a smoke assist fan to blow in the wrong direction. So they got the fan right, but didn’t know why?
And apart from all this, K’s are out there dutifully trucking around layouts across the land.
