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Author Topic: K-27 Gear Ratio  (Read 6601 times)
JLyans

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« on: April 04, 2008, 11:42:48 PM »

Hello Bach-mann,

I was just wondering if there has been any discussion or if there are any plans to address the problem of the 15:1 gear ratio on the K-27?  My K-27 runs smoothly but I can't run it double-headed with my Accucraft K-27 because the gearing is too high. I understand the intention was to have 30:1 gearing but this didn't happen. What would it take, a different gear box or a different output at the motor?

I don't think it was intended for these fine models to run a scale 80 mph at 18 volts.  Also, the model's operation would sure improve on both up and downhill grades, (especially uphill).

Do you know of any fixes for this problem? Thank you.

John
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the Bach-man
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« Reply #1 on: April 04, 2008, 11:58:29 PM »

Dear John,
I'm not sure what will eventually be done in this regard, but if anything is announced, I'll let you know.
Thanks!
the Bach-man
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Bud Steinhoff

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« Reply #2 on: April 05, 2008, 09:05:22 AM »

I was very pleased that the Bachman K ran as fast as it does with plenty of slow speed power.
If I had the Accucraft K I would try to gear it up to have the option of running faster than a crawl.
Bud
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Tony Walsham

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« Reply #3 on: April 05, 2008, 10:06:35 AM »

Sorry Bud IMHO you are wrong.
The problem with the K-27 is it doesn't have any slow speed lugging power up even a slight grade.
I know of one that cannot pull three Accucraft coaches up 2%.
No problem on the flat.

As to the speed.  I guess that is in the eye of the beholder. 

On 18 volts it gets up to about 80 scale miles per hour.
In real life the K-27 did not achieve much more than 30 mph in general use. 
If the K-27 actually had a gear ratio of 30:1 like it was planned to have, you could simply add more batteries to get to play slot trains.
A win win for everyone.
A realistic top speed, more pulling power and less current consumption doing it.
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Tony Walsham
Founding member of the battery Mafia.


(Remote Control Systems).
StanAmes


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« Reply #4 on: April 05, 2008, 12:35:51 PM »

Interesting discussion.  In my opinion, I believe that Tony and Bud have both correct and incorrect observations.

What’s missing is the voltage, control system they are using and a calibrated speed as one person’s slow is another person’s fast.

For example Tony says
Quote
it doesn't have any slow speed lugging power up even a slight grade.

Interesting observation.  I thought I would try it out.

On the level or running light on a 3% grade or running at full load on a 3% grade my K takes 78 seconds to smoothly go 1ft.  If I run the math correctly there are 5280 ft in a mile, that means about 260 ft equals 1 mile in scale of 1:20.32.  So that works out to about 0.2 scale miles per hour which is slower than most K27 operated at.  Note the pulling power on my railroad is limited by wheel slip and it is weight and not gearing that is going to affect wheel slip.

So clearly slow speed performance of is not a locomotive issue.  On my railroad my k27 has its top speed set for about 16 miles per hour which is rather fast for my railroad but well in the prototype range which for this locomotive would be a top speed of 30 mph.

Note that the performance on other systems will clearly vary.  For  example in DC the quality of the regulation and sensitivity of the power will also play a large role.

In order to have any type of serious discussion on speed one needs to have a graph of scale miles per hour vrs voltage.

The review in MR has one but I am not at all sure it is anywhere near correct as it seems to be a rather slow speed at 24 volts DC.

Once we can agree on the speed/voltage curve then we must discuss the max voltage.  Alas in large scale the max voltage is all over the place from 15 to 30 volts and the more voltage the more the max speed.

If you half the gearing you also half the max speed at any given voltage.

I am not saying the gearing is optimal or not as the a higher ratio may also result in a better motor efficiency.

All I am saying is that before we have this discussion we should be using real numbers and not subjective comments.  We should also have an understanding that user preferences are very different.  I have been constantly surprised at how fast some operate their locomotives yet also understand that the a mass produced locomotive has a wide range of users it must satisfy.

Stan Ames
www.tttrains.com/largescale
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Bud Steinhoff

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« Reply #5 on: April 05, 2008, 12:54:44 PM »

I agree with Stan and still am very satisfied with the pulling power at low speeds.
Mine pulls 8 loaded heavy kit cars up 4% grades with no problem.
I have added weight to the loco for traction and run 22 volts to the track through Aristo on-boards.
Don't have to worry about power consumption with my 25 amp Bridgewerks.
Pulls much better than the 2-8-0
Bud
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Greg Elmassian


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« Reply #6 on: April 05, 2008, 03:19:11 PM »

There's something wrong here. One person can't pull a few coaches up a 2% and another can pull 8 cars up a 4%.

I think we need to get consensus on the actual drawbar pull, and compare it to other locos before saying that something is wrong.

Note: I do NOT disbelieve Tony or Bud!

On the gear ratio, Stan, you quote running light. The point that was being made is pulling power, and that the gear ratio is too tall.

Running light is no test at all for a locomotive, they will go "straight up" with no load.

But first things first, like I said, what is the AVERAGE pulling power of K's? Maybe a few people can submit some more data. There CLEARLY is a disparity between what Tony reported and Bud reported.

Regards, Greg

p.s. proper gearing is more than just pulling power, and electronics cannot compensate completely for an inappropriate gear ratio... otherwise our cars would not need transmissions, just a bigger computer!
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Bud Steinhoff

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« Reply #7 on: April 05, 2008, 04:37:36 PM »

Greg, a larger motor will compensate for higher gearing and give low end power.
Big block/higher torque will pull taller gearing.
A Small block needs lower gearing/ twisted tighter to get low end horsepower.
Bud
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Greg Elmassian


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« Reply #8 on: April 05, 2008, 04:53:17 PM »

Yep, pretty familiar with motors in that sense. (I like torque!)

The point was given the SAME motor, the effect of gearing, and that electronics alone will not do the same thing as gearing.

Any chance you can do a drawbar pull on your loco on level, clean track?  (also type of track makes a difference).

Regards, Greg
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Bud Steinhoff

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« Reply #9 on: April 05, 2008, 05:24:17 PM »

 Track is brass, clean, dry, no oil.
Cars weigh an average of 3 lbs each with plain steel wheels.
Mine will not stall, it will slip first even with over 1 lb. of lead in it.
If the track has any oil on it the K will spin on the 4% grades.

Bud
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StanAmes


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« Reply #10 on: April 05, 2008, 05:32:24 PM »

I always enjoy the MR reviews because they provide actual drawbar pull, current load, and scale speed for the locomotive they review.  To me that provides a more objective review of a product and is invaluable information in the smaller scales.  Unfortunately. with the K27 review, it appears they must have used a wrong scale factor because the numbers do not match the numbers I get.

MR reports a max drawbar pull of 44 ounces.  I have no real way of measuring this to confirm this number and in Large Scale we all know the drawpull is effected by track type used and the age of the wheels.

MR reports that at 18 volts the K27 runs at 25 MPH.

Tony reports
Quote
On 18 volts it gets up to about 80 scale miles per hour.

I had some free time this afternoon waiting for some cement to dry so I measured it myself.

I am using an Aristocraft CRE-55465 switching power supply that has a very good regulated voltage at 13.8 volts, 19 volts,  and 24 volts DC.

I do not have a lot of level straight track so my numbers can be off but they should be in range.

At 18 volts I measure a speed of 41 scale MPH.  At 23 volts 69 scale MPH and at 13.8 about 33 scale MPH.  These numbers could be off 10% or so but its a good start.

So what does this tell us.

1) the MR reported numbers are way off too slow

2) the Internet numbers are way too high

I believe the design criteria for the K27 was scale speed at 14.4 volts so it would appear that the measured numbers are a little fast but not that far off from what I believe the intent was.

Does this make the gearing optimal?  Not necessarily.

What we as a modeling community need to do is to develop a recommended speed scale speed table for the various scales.  That would provide us an objective number to measure the model against.

Prototype narrow gauge locomotives ran slow and many modelers enjoy operating their locomotives faster than the prototype.
 
If the manufacturer designs locomotives with scale speed at 24 volts DC, then modelers operating at 14 .4 volts will have real slow locomotives and those that enjoy faster locomotives will not get the desired speed at top voltage.

This is not a simple question and clearly one that needs the community to come together on.

Some like it fast some like it slow.  What we need to do is to quantify a speed range that is just right.

Hope that helps

Stan Ames
www.tttrains.com/largescale
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Greg Elmassian


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« Reply #11 on: April 05, 2008, 06:17:07 PM »

A simple, inexpensive fish scale hooked to the tender coupler will measure drawbar pull.

Stan, you raise an interesting point.

I think that as long as simple DC track power (voltage on track varies) exists this will be  a question with no answer.

Ideally, the speed of the loco over the working voltage range would match the prototype. That would give you optimal control by giving you the highest "resolution" on your throttle.

But then comes the problem of double-heading locos on simple track power. In this case, you would probably like all locos (that would be reasonably doubleheaded or mu'd) to run at the same speed for a given voltage (assume current is unlimited).

Of course, combining a slower steamer with a passenger diesel is not unheard of.

This just won't have a good solution for simple track power.

What is happening though, is that I see a trend in remote control systems to support speed tables, where actual speed vs. throttle setting/speed step can be customized.

For me, in DCC, my druthers would be that all locos are geared/powered to match prototype, and that the typical max voltage would run the loco just a bit of prototype maximum (giving some headroom for voltage losses, speed matching, etc.)

But my druthers are not right for everyone, so the "right" answer must be somewhere between "true prototype" and "warp 1".

Clearly a 100 smph narrow gauge loco does not make sense.

Only time will sort this out, but looking at other scales, more reasonable top speeds have been an evolution. I remember some of my N scale stuff that would hit 260 smph.  Grin

Regards, Greg
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StanAmes


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« Reply #12 on: April 05, 2008, 06:52:50 PM »

Greg

I agree but with large scale there is an additonal problem. What should the max DC voltage be from a standpoint of max prototype speed.

In the smaller speeds we have a spec of minimum max voltage  at full load of12 volts DC.  No similar voltage spec in Large Scale.

What should the max voltage be from a speed standpoint in 1:20.3

The top voltage is all over the place in large scale.

Many battery systems perfer 14.4 volts DC for max prototype speed (like the K27)Bachmann and Digitrax have apparently chosen 18 volts for their systems,  the DCC specs have chosen 22 volts, LGB and aristo have chosen 24 volts DC and some over 35 volts DC.

And if the manufacturer selects 24 volts as a prototypical max speed then many others at the lower voltages will have very slow locomotives.

In my opinion, its a problem that we the Large scale community need to come to grips with before we start critisizing any particular manufacturer or product

No simple answer here. 

Stan
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Tony Walsham

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« Reply #13 on: April 05, 2008, 06:59:51 PM »

Stan.

As you were part of the consultations that took place during the design stages of the K-27, do you agree that 30:1 was the gear ratio proposed?

Do you agree that Bachmann decided that 29:1 was appropriate for the K-27?

If so, how come the K-27 has ended up with 14.5:1 and not 29:1?
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Tony Walsham
Founding member of the battery Mafia.


(Remote Control Systems).
petertoot

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« Reply #14 on: April 05, 2008, 07:22:44 PM »

stan,tony has an interesting point,as we all know,these beasts all have some little quirk to bug us,but as a community,of course these make good conversation,if anyoying.i have in some parts at least 4% ,the only way up,with 4 bachmann coaches,is two connies,on aristo track power,or that part of the line is not used,just my 2 cents have fun,cheeers peter in auzzie Cool Cool
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