Working on powered trucks

Working on powered trucks

Postby DKRickman » Mon Feb 17, 2014 1:58 pm

Hello folks,

First, a brief introduction, as I'm new here. My name is Ken Rickman, and I'm a locomotive engineer for Norfolk Southern. While I primarily model in HO standard gauge at the moment, I have always had an interest in other scales, gauges, and pretty much anything obscure, offbeat, or otherwise unusual. Some of you may have read the TT thread I started over at MRH.

So, if I don't model in TT, why am I here? Because I think I have something to offer. I've been working on some powered truck designs for my own use, because I'd like to try powering a small HO steam loco tender instead of the drivers, and there's just not much out there suitable. I started doing some research and coming up with some designs, and I realized that the design might be useful to some TT modelers as well. I've now got a preliminary design available on Shapeways, and I invite people to look at it, order it, try it, discuss it, etc. At the moment, I am making it available at cost because the design is completely untested. If/when it is proven to work, I plan on adding a small markup for myself, probably something in the range of $2.

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Image

This version of the truck has a 9' wheelbase and uses NWSL P:87 28" wheels, or 39" in TT. I designed it with the GP38-2 in mind. With 13mm of space inside the shell, it should have at least 12.5 degrees of rotation in each direction - more than enough for a 12" radius curve.

Provided that this design works, I intend to offer several versions. It's easy to make pretty much and wheelbase you want - no more 9'2" compromise between a Blomberg and an AAR Type B. I have also made the design with three axle trucks in mind, so a truck for the SD45 is high on the priority list. Also, I have designs in the works using smaller motors, which should help with some really tight applications, and with no motor at all, to be driven by a shaft from a powered truck.

I've read the thread about the U30B (it's one of the things that inspired me to start working with Shapeways, in fact), so I have some idea what challenges Alex faced in producing his model. I don't claim to be any smarter or better, but I do think that I have a different idea that might work better in this case.

With that, I look forward to helping the TT community and seeing if we can't make something new and better. Ideally, I'd like to see a greater range of models produced, and I want to help make that happen.
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Re: Working on powered trucks

Postby ctxmf74 » Mon Feb 17, 2014 2:57 pm

Glad to see someone working on a TT scale drive. If the axle bearings and gears are readily available and of good quality it might be worth making a version with the upper belt drive pulley running on a shaft instead of a motor so a larger motor could be frame mounted between the trucks and connected to the belt tower with U -joints. ...DaveB
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Re: Working on powered trucks

Postby Rob M » Mon Feb 17, 2014 3:04 pm

Nice :thumbup: You're about to have a lot of new friends!
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Re: Working on powered trucks

Postby DKRickman » Mon Feb 17, 2014 3:10 pm

ctxmf74 wrote:If the axle bearings and gears are readily available and of good quality it might be worth making a version with the upper belt drive pulley running on a shaft instead of a motor so a larger motor could be frame mounted between the trucks and connected to the belt tower with U -joints.


I've thought about that as well, Dave. The only thing I would need to know is the desired height of the drive shaft. If somebody has a lathe and wants to tackle the project, it would be easier to use a 1.5mm or 2mm shaft with a V cut into it rather than mounting a separate pulley on a 1mm shaft.

The gears are Tenshodo, available from Nigel Lawton. The bearings are either 3D printed (included in the drawing), or the truck is designed to accept miniature ball bearings on all of the shafts.

One thing I want to know, though, is just how powerful the 10mm x 12mm motors are. It seems to me that truck mounted motors are more desirable from a packaging point of view, but that would obviously have to depend on the trucks being powerful and durable enough. Cost would also be an issue, or course.

Rob M wrote:Nice :thumbup: You're about to have a lot of new friends!


I hope I don't disappoint any of them! I really think this design will work, but I have to stress that it is untested at this point. Aside from power, as noted above, I do not know how long the 3D printed bearings will last. I think they'll work well, but I don't know.
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Re: Working on powered trucks

Postby Rob M » Mon Feb 17, 2014 3:20 pm

If you make the hole in the plastic/shapeways bearing 3mm you can insert some 3mm brass tube from K&S for bearings. It is a perfect fit for 1.5mm axles.

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Re: Working on powered trucks

Postby DKRickman » Mon Feb 17, 2014 3:49 pm

Rob M wrote:3mm brass tube .. is a perfect fit for 1.5mm axles.

Good information, Rob! The ball bearings I designed around are 1.5x4x2 (and 2x5x2.5 for the axles), so there's certainly room for 3mm brass tube. In fact, it should be pretty easy to open the hole in the printed bearings and insert a length of tube in there.

I like knowing that there are options. And since I plan on building a few of these (in HO scale) for myself, I may need those options too!
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Re: Working on powered trucks

Postby ConducTTor » Mon Feb 17, 2014 7:34 pm

Hey Ken welcome aboard!

A few things:

Small motors on each truck *may* be enough especially if there's a flywheel. I think a flywheel is a must have for good driving characteristics. I've also started thinking in the direction of a motor per truck (if the MTB trucks don't work out for some reason) however my thought is that the motor is vertical. It would be in the center of the truck. The motor body itself would be the pivot for the truck. That presents a problem with the length of the motor for the short front hood.

As for Shapeways, I would design with bearings in mind. The WSF material is not slick enough and causes too much friction if an axle is directly on it. The "detail" materials are better in this regard but they require a lot of cleaning and can crack under stress.

Not trying to discourage you at all - just saving you from learning some lessons. I look forward to what you come up with.
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Re: Working on powered trucks

Postby areibel » Mon Feb 17, 2014 7:42 pm

Hi Ken,
I see you found the place, Welcome!
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Re: Working on powered trucks

Postby DKRickman » Mon Feb 17, 2014 8:26 pm

Flywheels:
As much as I like flywheels, they take up space. They also add a significant load on the motor bearings (assuming that they are on the motor shaft), and I have concerns about doing that to these small motors. Also, I feel that if the mechanism is smooth enough, a flywheel isn't needed. DCC can do a lot as well, if it's an option.

Vertical motors:
I tried to come up with a design using vertical motors, for the reasons you describe. However, I wasn't able to come up with a suitable design, especially one which can be adjusted for different wheelbases. I did come up with a concept which uses 6mm motors mounted vertically, one per axle, but that gets expensive fairly quickly, and I'm not sure there's any real benefit to it.

Bearings:
The design I posted does incorporate bearings. It is designed to allow the use of ball bearings, and I have included simple WSF bearings of the same dimensions. I am intrigued by your comments on the suitability of WSF for bearings, as my (admittedly minimal) experience with the material suggests that it can work well if the hole is the right diameter.
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Re: Working on powered trucks

Postby ctxmf74 » Tue Feb 18, 2014 12:41 am

"I've also started thinking in the direction of a motor per truck (if the MTB trucks don't work out for some reason) however my thought is that the motor is vertical. It would be in the center of the truck."

Usually they mount vertical motors offset from the truck pivot point so the motor gear can mesh with the rear axle gear(on the front truck, front motor gear on the rear truck) The power from the rear axle to the front axle is by open spur gears. This is a common drive for O toy trains to allow the center of the loco to be open space for their oversize sound systems. The problem is it's hard to design a low speed gearing when driving the rear axle directly from the motor gear so they tend to jump start like a rabbit and run at 150 MPH top speed. It's a much more flexible design to use the gear tower and mount the motor farther away from the axle, either like Ken has done with the belt drive or with U-joints to a frame mounted motor. With the motor frame mounted between the trucks it can be wider as it doesn't need to swivel like a truck mounted motor does and it has more distance from the truck gearing for flywheels and U -joints. It's gonna be hard to design something better than the Saz model switcher drive so giving them the incentive to produce and sell drives to everyone would be a good way to go......DaveB
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