Recommended NWSL Gear Ratios for Steam Locos?

[Trainman440]

Hi guys, Im trying to get into gearing and repowering for my brass engines (as seen by my previous post)

A year ago I replace all my brass engine's motors with Mabuchi and Sagami (when available) motors. I also replaced the tubing with some non-concentric tubing by accident and am currently finding a better source for tubing. 

Anyways, I've come to the conclusion that for some of my PFM models, the gearboxes are just noisy, no matter what I do. One even seems to have started cracking from zinc pest. 

So, Im making a list of things to buy from NWSL. I want to replace the gearboxes for:

1. PFM/United ATSF 2-8-0

2. PFM/United Sou PS-4

3. Tenshodo ATSF 4-6-4

All common/old brass engines that run well, but noisy. 

I know there's no rule for gear ratios, and its often personal preference, but what kind of gear ratios do people go for? I heard 14:1 and 28:1 are preferred. Which one would you choose?

Also, I heard 0.4 mod is used for heavy HO engines and 0.3 mod for light. Would a 2-8-0 be classified as heavy?

Thanks,

Charles

[RR_Mel]

As I remember the Rivarossi articulated ratio from motor to axle is 16:1.  I have forgotten the ratio of the gearbox, been too many years.  

I have a spare driver assembly and just checked the axle gear ratio at 3:1 so maybe 13:1 gear box.

Rivarossi Cab Forward motor 2880 RPM to wheel 180 RPM = 60MPH HO Scale, from my 12 year old notes.

 EDIT:

I remembered wrong, I opened up a Cab Forward and the total (gearbox and axle) gear ratio is 19:1.

Mel



 
My Model Railroad   
http://melvineperry.blogspot.com/
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 

[Paul3]

One of the issues here is if your steamers are going to be DC or DCC.

I have put DCC decoders in many a brass steamer, and on an 18VDC layout they run at a good prototypical speed.  However, drop a decoder in the same engine and top speed takes a big hit because usually only 12v passes through the decoder to the motor.  Now, if the engines follow NMRA Recommended Practices, 12v should be a loco's top prototypical speed.  But that doesn't always happen.

Most of the locos that I have problems with have a 36:1 gear ratio and run a top speed on DCC in the high 30'/low 40's.  If I convert to a 28:1, my top speed should be around 60mph, which is fine for my brass freight steamers.  If I have a passenger steamer, I might consider 14:1, but I'd have to run the numbers.  Remember that figuring out the ratio is just counting the teeth on the spur geat that mates to the worm gear; 14 teeth = 14:1 ratio.

As for gearbox size, buy the biggest one that will fit.

And if you're doing that many engines, I hope you have the gear puller and the quarterer.  It's worth it.  Just remember to always pull the non-insulated wheel when changing driver axle gears.  Never pull an insulated wheel; bad things can happen (as it can come apart).

[gmpullman]

Hello,

Have you looked at this handout from an NMRA Clinic before?

http://schutzer.net/Brass_Clinics/RebuildingBrass2008a.pdf

Some basic information but you may find it helpful.

Good Luck, Ed

[Trainman440]

Hi, yes, Ive read up on a ton of info and watched some videos on it (notably the linnk you sent above, CW Railman, Darth, repower and regear groups.io, and some other forum threads. However very few ever mention the gear ratios, mods and etc (the questions I posed above). That's why I asked them.

I appreciate the replies! Looks like 1:28 is a good standard ratio. I might try 1:36 for small switchers, and maybe 1:14 for a brass pacific, but from seeing how some regeared 1:28 engines run, they already achieve a pretty good top speed (although I havent accounted for motor rpm or max voltage, Im running NCE DCC, which I believe is 13v)

I'll probably try out a 1:28 gearbox for myself and see how it performs before buying more.

I'll probably open up a few engines just to see their gear ratios. @paul3 From what Im gathering, the amount of teeth on the worm gear determines the gear ratio right? How would you determine the gear ratio of a gearbox with an idler?

Charles

Charles

[Darth Santa Fe]

The gear ratio will depend on the speed you're wanting, as well as the motor used.  With steam engines, I usually try to get a drive wheel speed of 300RPM for slow to medium freight, or 360RPM for passenger and high speed freight.  Getting these speeds figured out is pretty simple with basic calculations.

Assuming a 10,000RPM motor is used, the 28:1 gears will get you almost exactly 360RPM, while the 36:1 gears will get you about 280RPM.  With 50" drive wheels, that's about 54 scale MPH with 28:1 gears or 42 scale MPH with the 36:1 gears.  With 80" drive wheels, you'd hit 86 MPH with the 28:1 gears or 66 MPH with the 36:1 gears.

Also, for figuring out what the speed will be based on wheels diameter, here's the calculation to follow:

Wheel diameter in inches / 12 (convert to feet)
Diameter in feet X pi (find circumference)
Circumference X RPM (feet per minute)
Feet per minute / 5,280 (miles per minute)
Miles per minute X 60 (miles per hour)

[richg1998]

It has been quite a few years ago but I bought the gear planning info from NWSL when they where still in Seattle, Washington and built some gear boxes for steam engines, plus the Puller and Quarterer, plus flywheels, worms, worm gears and spur guears. I liked the MDC, Roundhouse 45 to . 72 to 1 for switchers.

I think the gear info is still on their site.

Rich