[ggnlars]

While working with the Rapido CN RS-18, one of the ways to push the motor was to run at increasing larger grade levels. These results were different than expected based on what has been implied in other discussions. To get a better understanding of this, a series of experiments were devised to see how this engine would compare with others. A side benefit of this exercise would be actual data on how there engines respond to changes in track grade and train load (length).
As usual, each test brought more questions. To help understand these, an systemic approach was developed.
This approach, the initial data base, and results are shown here:

https://youtu.be/ZX31KlOcxdM

More details are shown on my site.

 

[Fire21]

Well, I watched half of your video, and I'm sorry, but I have no idea what all your figures and charts mean. I gave up. I guess I'll just run my trains on lengths and grades that they'll operate well on. Thanks for your efforts! :smilie_daumenpos:

 

[DonR]

Very interesting study. You've sure put in some thought
and time to provide it.

However, unless I missed seeing it in all of your details,
I don't find any consideration for the WEIGHT of the locos.

I've never actually seen an HO loco STALL when trying
to pull a long train. What does happen is the wheels
lose traction and spin. But when you add weight to that
same loco it gains traction and can pull more cars before the spin.

I had a pair of Bachmann GE 70 ton switchers. Out of
the box they could pull few cars due to wheel slip.
But after I added weight inside the shell they were just as 'ABLE' as any of my locos.

It would be interesting to see a repeat of your experiments
by using a specific loco. Determine the number of cars it
pulls UNTIL WHEEL SPIN. Add weight and repeat.
Add more weight and repeat...and so on. You may need
more than an 8 foot track as you add weight and cars. You could,
for this experiment, simply add weight to the top of the loco.
I used 1 ounce lead segments cut from a strip available
at local hobby shop. Other's have used fishing weights.

I don't think I've ever seen a trial such this. It may
be helpful to many of our members.

Don

 

[D&J Railroad]

Your video cuts away to quickly from the last data line that you transition into on each page of the video. Have to keep stopping the video to back up, read then determine where on the chart it applies.
You might try just putting all the data on the opening page instead of exercising your transition features. They are distracting.

 

[gregc]

from my observations, like the prototype, the maximum tractive effort of a locomotive is typically 25% of its adhesive weight (balanced weight on all the drivers). I've found 20% to be a minimum for the tractive effort of a model (it's not quite the same as steel wheels on steel rails).

but the variable is the rollability of the trucks on the freight cars. I've found a lot of variation. I believe an acceptable level is that a truck rolls on its own on a 2% grade.

we measured a pulling force 2.4oz on 30 cars estimated to weight 4 oz. this comes out to 2% (2.4 / 120oz). the same as the additional force going up a 2% grade.

this understanding can help a modeler predict performance and recognize realistic expectations. determine how much extra weight would need to be added to a locomotive and if it's practical (is there room). determine if some trucks need tuning or replacement and if that would be enough

 

[MichaelE]

What happens to the figures when two of eight drivers have traction tires?

 

[mesenteria]

Depending on the locomotive, and on what you add in the way of rolling stock to the trailing cars to see the net gain (their condition will not be accounted for, only IF the locomotive can pull it/them), it is generally near 40% more, but it could be substantially more.

 

[gregc]

What happens to the figures when two of eight drivers have traction tires?

i don't know. i'd have to measure.

i have an old Mantua 0-4-0 goat that has one rubber traction tire. the loco (not including tender) weighs 6.5 oz. It pulled 1.23 oz with wheels spinning, or 19% (1.23/6.5). It hasn't been run in years and the rubber may be hard.

i expected more, but that's a measurement, not an educated guess. And that's my point - measure things to determine if there's room for improvement.

 

[SantaFeJim]

I tried to watch your video. I am guessing that you spent a good amount of time gathering your data, drawing charts and graphs as well as all the flashy automation.

HOWEVER... it is sensory overload. I found it harder to follow than first semester of Chinese Algebra.

 

[blackz28]

i loved it but am suprised that the 4-6-6-4 didnt do better

 

[ggnlars]

A number of people have complained about the video transitions among other things, I will take note of that in the future.

It seems that several are wanting to use a simple derivative approach to this problem. Motor performance is not linear and thus the linear approach will not always yield the result your looking for.

At this point, I am not necessarily looking for the best approach to yield the longest train length and or the highest grade. At this juncture, I am looking for what do the performance characteristics for a random set of engines look like.

The following chart is shown in the video with additional animation and explaniation:

/Users/lawrencedunbar/Pictures/Photos Library.photoslibrary/resources/renders/1/1131B976-69E4-4C2B-9106-95EAD998D688_1_201_a.jpeg

The y-axis is the total car weight divided by the quantity of the engine weight on the drive wheels times the ratio of the drive wheels divided by 8.
This normalizes the results. Because the track segments are the same and the cars are the same, the the differences are from the engines. Primarily from the motors.

There are a number of things that come mind. The motor operating condition to the design relationship is a primary factor, this is when the operating point has put the motor torque output near its maximum capability. Others include the strength of the magnet flux, the condition of the electromagnetic poles and the internal motor bearing drags.

If these are the case, adding weight will not add more pulling capability.

Clearly the data indicates that one rule of thumb is not adequate.

The number maximum number of cars on the video charts is the largest number that can be pulled up the grade three times. For this case, all the drive wheels were slipping to some some degree. When the wheels start to slip the current draw shape changes.

The purpose of this set of experiments was to define an initial set of data base characteristics. With this insight comes many questions. Where possible & of value, I will work to answer some of these.

 

[mesenteria]

…

Clearly the data indicates that one rule of thumb is not adequate.

...

Correct, and many of us who have a bit of experience and history in the hobby have maintained this all along. Doing mock-up trials is about the best way to determine whether one's grades, grades with curve compensation, eased curves vs. purely radial curves, and typical consist resistance as trailing 'tonnages' will work on a given track plan.

There are so many confounds: track laying skills, variances in assembly and quality/mechanical condition of the drive mechanisms, lubes that change from model issue to model issue, lubes that are old and more sticky, and so on.

 

[D&J Railroad]

Bottom line: Results may vary.

 

[T-Man]

A simple way is to look at the helix. The information on how to build them is out there.

 

[ggnlars]

Have been asked what my G&TL studies mean to a persons layout. That is an open question. It depends on a number of factors.
The track resistance was intentionally set to be minimal.
1- Even at that I was surprised at the pulling capability at grade. Nine of the twelve pulled 2X the drive wheels at 4% grade. If you assume a worst case of 1.5% grade of track resistance in a helix or complex nolex, then 2.5% grade is doable in a layout design.
2- The ability to pull a few cars at 11% grade was a surprise. This has ramifications for certain types of trains and layouts.
3- the change in scale velocity with load was less than expected prior to wheel slip.
After wheel slip there is a limited number of additional cars that can be pulled up the grade.

The above can be drives from the data taken using the current techniques.

Additional insight can be achieved by examining a number of one, two or more off variations. This would be done on selected engines. These might include:

1- increasing the engine weight, by 3 steps for a total of 1 pound. This may be academic because it may be impossible to add that much weight. It will get at the motor capacity and the grade impact of the weight change.

2- motor variation, Kato, Athearn Genesis, Mashima, etc
The
3- general tune up

4- electronics, DCC, Rail Pro, etc

This list is by no means complete. I would be interested in hearing other ideas from you all.

 

[gregc]

Additional insight can be achieved by examining a number of one, two or more off variations. This would be done on selected engines. These might include:

1- increasing the engine weight, by 3 steps for a total of 1 pound. This may be academic because it may be impossible to add that much weight. It will get at the motor capacity and the grade impact of the weight change.

2- motor variation, Kato, Athearn Genesis, Mashima, etc
The
3- general tune up

4- electronics, DCC, Rail Pro, etc

in general, i believe modelers start asking questions about performance when a particular locomotive is unable to pull a train up a grade. the assumption is that pulling power depends on the number of driving wheels or even locomotive length

the reality is pulling power depends on friction which depends on weight just as it does for the prototypes.

i thought the video suggested something about motor characteristics, but i don't believe there is any evidence of a motor stalling and not simply slipping. in other words, the motors have enough force to push the wheels and it's a question of traction -- friction and weight

replacing a motor, tuning up the motor or replacing motor drive electronics are not going to increase the number of cars being pulled

of course if there's no room to add weight, there's not much you can do, but it's surprising how heavy some small engines weigh

 

[ggnlars]

I have run documented engine only tests on over 400 HO engines. In these I measure the draw bar force, amount other things. In some of these tests I have separately changed the motors, the electronics, the lubrication and the weight. In all of these I saw some force increase. Some times several implied cars worth. Often adding the weight did not increase the force and the engine wheels did not slip. I am looking to see what that translates to. Is it true at all grades? Does it disappear as grade is increased.

 

[Dennis461]

ggnlars

I have a thought. Could you develop a method which we could all use to get you more data? Perhaps some device on a flatbed car we can connect behind our engine, pull cars (adding more) until slippage occurs, then report the data?

Cut down on variables by requiring the test be done on nickle silver rail, 0% grade.
The flat car with device would be shipped around the county with a refundable deposit.

https://www.homesciencetools.com/product/spring-scale-100-g-1-n/

 

[gregc]

Often adding the weight did not increase the force and the engine wheels did not slip.

by "wheels did not slip", do you mean the engine stalled (stopped turning)?

 

[65446]

Though your efforts are admirable, I don't see its need. Here's why:
If one's MRR has no more than a 2, 2.5, 3% grade (3 being iffy), knowing what tractive effort each of our locos has, doesn't change anything as to their ability to lift cars up these grades. Either way it's still the same for each engine. What are our choices ? We can leave them alone, add weight, traction tires, put smaller wheels on our steamers, r&r their motors. The Riv y6b, Bachmann Northern, the Atlas S4, the Key Imports 2-8-0 will do what they can do after these considerations. We all find that out soon, anyway; The Connie can lift 8 cars, the y6b,18, the Northern, 8 passenger cars.
Hey, it's a hobby, not a banking corporation stress test. In other words, though your testing method may be astute, it doesn't change the facts of the engines' abilities on the RR, when off the drawing board.. :smokin: