Loco Frame - Truck Gearing

Loco Frame - Truck Gearing

Postby ConnRiver » Fri May 20, 2016 11:34 am

I've disassembled a geared truck from a Proto 2000 GP7 I have here to study the internal elements.

Assuming a tower truck with a worm gear, I'm thinking a final gear ratio of 14:1 (a preferred ratio by some or most members of the Diesel List for road locos) for a TT four-axle power chassis. Any thoughts?

Also, have been reviewing gear-making information I have on hand and searching online as well. Some of the topics deal with cutting one's own masters and casting copies, so I would guess home shop production is a possibility. Need to explore this further.

Might someone here know of a source for mini/micro involute and worm gears at reasonable prices? I'm thinking NWSL prices might be too high to tolerate. . . .

Thanks much, Brian C. / Cedar Rapids, Iowa
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Re: Loco Frame - Truck Gearing

Postby Bernd » Fri May 20, 2016 4:24 pm

ConnRiver wrote:Assuming a tower truck with a worm gear, I'm thinking a final gear ratio of 14:1 (a preferred ratio by some or most members of the Diesel List for road locos) for a TT four-axle power chassis. Any thoughts?


I would determine the ratio for a speed of 60 to 70 miles per hour with a 12 volt motor running at 12 volts. This should then give you a better lower speed. I believe the engines, no matter what scale, all run to fast at wide open throttle.

Also, have been reviewing gear-making information I have on hand and searching online as well. Some of the topics deal with cutting one's own masters and casting copies, so I would guess home shop production is a possibility. Need to explore this further.


Having worked for 30 years for a machine tool manufacturer that made gear cutting machines for the auto, areo, recreation and military industry I'd say this would be a daunting task. It takes some precision machinery to cut gears. Yes you can do it on a mill. I have done that. For precision you will need involute gear cutters. These are not cheap. Then think about how you will sharpen them once dull. The best gears for quiet operation are helical spur gears. That takes a hobbing machine and hobbing cutters. Again an expensive proposition. For mass production of gearing I'd say your best bet would be plastic injection. The above is strictly my opinion based on gear knowledge from a manufacturer I used to work for.

Might someone here know of a source for mini/micro involute and worm gears at reasonable prices? I'm thinking NWSL prices might be too high to tolerate. . . .

Thanks much, Brian C. / Cedar Rapids, Iowa


I would do a search on mini/micro gearing. Also I've seen on E-bay sources for small gears that could be used in model locomotives.

So there you have it, my opinion. YMMV.

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Re: Loco Frame - Truck Gearing

Postby ConnRiver » Fri May 20, 2016 4:28 pm

Thanks, Bernd. She who must be obeyed is telling me right now is the time to leave for a wedding. I'll be back Sunday, with a couple or three questions, no doubt.

-Brian C. / Cedar Rapids, Iowa
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Re: Loco Frame - Truck Gearing

Postby Tom Dempsey » Sat May 21, 2016 1:04 pm

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Re: Loco Frame - Truck Gearing

Postby krokodil » Sat May 21, 2016 4:19 pm

The overall ratio should be bigger than 14:1. For good running models the ideal ratio is between 20:1 to 30:1. ( I built about a dozen TT locomotives). In some models I used NWSL gears. The recent motors are much more faster as the old Zeuke motors were (5000 rpm vs. 15000)
For the gears it is really much easier to use industry made plastic gears. In Europe we use fine gears with Modules 0,4 or 0,3. Similar to DPI (see the conversion, unfortunatelly the two standards are not compatible). The M0,3 is already very fine for home made models, you need very accurate tools as the teeth are only 0,6 mm tall! Almost a clockwork. You need the fine teeth because otherwise there is no space for the reduction.
Last edited by krokodil on Mon May 23, 2016 2:12 am, edited 1 time in total.
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Re: Loco Frame - Truck Gearing

Postby Bernd » Sun May 22, 2016 5:18 pm

krokodil wrote:The overall ratio should be bigger than 14:1. For good running models the ideal ratio is between 20:1 to 30:1. ( I built about a dozen TT locomotives). In some models I used NWSL gears. The recent motors are much more faster as the old Zeuke motors were (5000 rpm vs. 15000)
For the gears it is really much easier to use industry made plastic gears. In Europe we use fine gears with Modules 0,4 or 0,3. Similar to DPI (see the conversion, unfortunatelly the two standards are not compatible). The M0,3 is already very fine for home made models, you need very accurate tools as the teeth is only 0,6 mm tall! Almost a clockwork. You need the fine teeth because otherwise there is no space for the reduction.


The above post is why I think using a drive similar to Holloywood Foundry belt drive to a worm and worm wheel is the ideal drive system. The pulley's allow a better adjustment of final drive speed by tweaking the diameters on hhe drive pulley and driven pulley diameter. Just my 2¢ worth. (Not adjusted for inflation)

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Re: Loco Frame - Truck Gearing

Postby krokodil » Mon May 23, 2016 2:10 am

Many years ago - when the flywheels became popular - I made several tests and constructions with belts. I was not very happy with the results. The belt on high speed (motor axle) requires lot of energy - ie it brakes the motor wheel and eliminates the flywheel effect in our size (would require much bigger flywheel). The belt drive is acceptable on second stage, after the first gear reduction.
The best reduction chain from my opinon is the motor with flywheel and a wormgear reduction to the second stage. From here does not really matters what we use for transmission (belts, gears etc.).
The wormgear used in last stage (driving the axles) is acceptable, but the whole chain will be noisier because more parts are running on high speed. This mechanizm without flywheels (like in the early Zeuke locos) has a problem with a sudden stops ( in front of the signals). The whole kinetic energy is absorbed on the last stage (wormgear on the wheels) what can easily damage the gears on axles.
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Re: Loco Frame - Truck Gearing

Postby ctxmf74 » Mon May 23, 2016 5:50 pm

"The overall ratio should be bigger than 14:1. For good running models the ideal ratio is between 20:1 to 30:1"

It depends on the motor used and the driver diameter. Older Athearn HO diesels were fine runners with a simple 12:1 gear ratio. I haven't checked the ratio on my SazModel switchers but they run great with probably around a 15:1 ratio.....DaveB
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Re: Loco Frame - Truck Gearing

Postby krokodil » Tue May 24, 2016 12:12 am

The early motors run at around 5-6000 rpm, today most of the motors run with >10000rpm. The commercial models in most cases are anyway too fast, ie some speed reduction is more than welcome :-)
In most cases the overall reduction in commercial models is an economy question ( how much gears and how much precision is optimal).
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Re: Loco Frame - Truck Gearing

Postby ConnRiver » Tue May 24, 2016 11:36 am

Mashima 1024D Motor dwg & specs.jpg
I work part-time, seven days a month. I'm off the next eight days, I'd really like to get a jump on working through what a power chassis might look like in this period. I have a lot to learn, could use suggestions from my buds here.

I have a reasonable concept of what the design of spur/involute gears entails. What I'm missing at the moment is the relationships between motor rpm and the final gear ratio. If there's a consensus that a Mashima 1024 is a fine motor, maybe experiments can start here?

Considering road switcher gearing (opposed to yard switcher), 40-inch wheels (a factor?), and a Mashima 1024, is there a reduction ratio we can generally agree upon?

-Brian C. / Cedar Rapids, Iowa
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