Custom Parametric Diesel Mechanisms

[dcutting]

I've been kinda quiet lately... school and things have been getting in the way. I would like to present my latest project, a fully parameterized N scale mechanism that can be customized to create almost any diesel locomotive's mechanism, including switchers.

One of the biggest upsets to my previous endeavors to bring you guys models of the C415, C636, and other units has been the lack of appropriate mechanisms to use as donor units. The work required to modify mechanisms is too much, and in some cases it just isn't possible to shoehorn an existing mechanism into a design. Designing a new mechanism for each new locomotive is possible, but time consuming and risky because one mistake can make if unusable.

Given these problems, I have begun development of a parametric mechanism. I am writing it all in python, using SolidPython to bridge to OpenSCAD. Components are sourced from NWSL, shop.kkpmo.com, mcmaster, and a couple of other sites. To top it all off, the frame will be 3D printed, along with the gearboxes and motor brackets, among other parts.

At the moment development focus is on the tank mechanism used in the Kato NW2. Many design practices are being borrowed from the NW2/mid SD40-2 design. I've attached a picture below of the latest rendering. While it looks very crude, this is the framework that will soon develop into a much more complex model. There's well over 200 parameters at the moment, and they include things like bogie spacing, number of axles, motor type, flywheel type, and hood width.

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I don't plan to release the source code at the moment, but at some point I might. If anyone here wants to assist in development or has suggestions, please let me know.

[peteski]

I have couple questions:

Why did you chooses that particular (oddball, and often problem prone) high-mounted motor design over the standard design used on most N scale loco where the motor drives the chassis-mounted worms directly?

Are most of the components (including truck and motor gears) will be 3D printed?  I assume that the worms and wheel-sets will be commercially available items. How about the axle bearings/pickup plates?  Etched brass or PB?

[sirenwerks]

Whatever you just said, David, if it brings us the chance for custom-length drives that can be used under oddball models like the C415 or an AS616, I am all for it.

[dcutting]

I have couple questions:

Why did you chooses that particular (oddball, and often problem prone) high-mounted motor design over the standard design used on most N scale loco where the motor drives the chassis-mounted worms directly?

Are most of the components (including truck and motor gears) will be 3D printed?  I assume that the worms and wheel-sets will be commercially available items. How about the axle bearings/pickup plates?  Etched brass or PB?

To answer your questions:

This type of mechanism can be fit into smaller locomotives while keeping a larger motor. It also takes less space inside of the model for gear towers, so the whole thing is heavier. What makes you say it is more problem-prone?

The trucks will be printed, but the gears will all be machined from delrin and brass, from off-the-shelf components. The pickup plates will be etched, and I will be designing a special tool that presses the points in it at adjustable intervals.

[RAILCAT]

Would not a much simpler design be a low profile self powered 4 and 6 wheel truck with variable axle spacing. Using the very small coreless motors as Kato and the newer Bachmann locos use. Less gears, no drive shafts.

[peteski]

To answer your questions:

This type of mechanism can be fit into smaller locomotives while keeping a larger motor. It also takes less space inside of the model for gear towers, so the whole thing is heavier. What makes you say it is more problem-prone?

The trucks will be printed, but the gears will all be machined from delrin and brass, from off-the-shelf components. The pickup plates will be etched, and I will be designing a special tool that presses the points in it at adjustable intervals.

Thanks Dave! How about the wheels themselves?

If you were to use the Kato NW2 unit, the spur gears were prone to cracking and slipping in the shaft.  That Kato motor is quite a bit smaller than the standard N scale Kato motor, but it has only a 3-pole skewed armature. Some modelers turn their noses at 3-pole motors. But if the power unit will be made by you then it shouldn't have that problem.   Also, if you were to orient the motor so the flat sides are vertical then you could make even a narrower chassis.

[nkalanaga]

Will you be able to make Nn3 mechanisms (new trucks would be the only difference) for "standard gauge" locomotives, such as the WP&Y's DL535Es, the Army MRS units, and many export units?  I'd love to have a bunch of RSD mechs for the early Atlas/Kato RS-3 bodies, instead of having to use MT Z SD40-2s.

[dcutting]

Will you be able to make Nn3 mechanisms (new trucks would be the only difference) for "standard gauge" locomotives, such as the WP&Y's DL535Es, the Army MRS units, and many export units?  I'd love to have a bunch of RSD mechs for the early Atlas/Kato RS-3 bodies, instead of having to use MT Z SD40-2s.

That's definitely within my capabilities here. Here's the trucks with both N and Z spacing:

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By making the gears smaller, we could probably also get some smaller wheel sizes going.

[nkalanaga]

Looks promising.  For the units I'd be interested in, 40 inch wheels would be correct, just like standard gauge.  Only the gauge changes.  But if you can do smaller wheels, that would open a lot of other possibilities.

[dcutting]

Thanks Dave! How about the wheels themselves?

If you were to use the Kato NW2 unit, the spur gears were prone to cracking and slipping in the shaft.  That Kato motor is quite a bit smaller than the standard N scale Kato motor, but it has only a 3-pole skewed armature. Some modelers turn their noses at 3-pole motors. But if the power unit will be made by you then it shouldn't have that problem.   Also, if you were to orient the motor so the flat sides are vertical then you could make even a narrower chassis.

Wheels are currently going to be sourced from NWSL. I'm trying to work with my gear supplier to have them make the split-axle gears.

[nkalanaga]

I've used NWSL wheels.  Expensive, but I've never gotten a bad one.  For locomotives they're worth the price.

[dcutting]

It's been slow in coming, but I've finally got the basics down. The geometry for all the gears and trucks is defined, so next comes the frame and the motor bracket. This easily represents over 100 hours and 1000 lines of code sunk into this project, but it's so awesome to just sit there and mess around with parameters and see everything change.



David

[mmagliaro]

David,
What module gears are you planning to use?   Standard N Scale stuff uses mod 0.3, but if you go to mod 0.2,
you can get about a 40% speed reduction, which will let the motor rev higher, and get much more low-end power.
It won't harm the top speed running at all, because typical "Kato geared" stuff always runs way too fast at full voltage anyway.

I bring all this up now because I know from experience how much better a low-geared driveline works.  I'm not proposing
you gear these down to the super-low speeds I tend to like in my own engines.  I'm just suggesting that with mod 0.2 gears, it would be a lot easier to build mechanisms that top out around 60-70 mph at 12 volts, which is ideal for model railroad use.

[dcutting]

David,
What module gears are you planning to use?   Standard N Scale stuff uses mod 0.3, but if you go to mod 0.2,
you can get about a 40% speed reduction, which will let the motor rev higher, and get much more low-end power.
It won't harm the top speed running at all, because typical "Kato geared" stuff always runs way too fast at full voltage anyway.

I bring all this up now because I know from experience how much better a low-geared driveline works.  I'm not proposing
you gear these down to the super-low speeds I tend to like in my own engines.  I'm just suggesting that with mod 0.2 gears, it would be a lot easier to build mechanisms that top out around 60-70 mph at 12 volts, which is ideal for model railroad use.

I'm using M0.2 gears, that was the plan from the outset. I've got some different suppliers that can get me just about any size and diameter, so that's really convenient for this project.

David

[daniel_leavitt2000]

Dave,
Have you thought about using a Tomix chairs as a parts source? That could really cut down on the costs of the motor, gears, worm and trucks. The trucks use needlepoint axles but without side frames.