Best Of The TP56/TP70 Kitbash thread N scale

[JanesCustomTrain]

Here is the front of the truck.   This might not work because maybe you can't remove material from the cover because that spot holds the worm bearing.




So let's try the other end.  This is my first choice.  Room seems to be better.
Disadvantage is that we have to couple the shafts somehow.

One possibility might be to trim the Kato SD40-2 cup and use it like a joiner to join the shafts.

Another possibility might be to cut and splice the B unit grey shaft and make it VERY short.
If that works, a Shapeways part might work.

With a longer shaft there could be a small flywheel put in front of the gear tower. Motor, worm, flywheel.

Jane

[randgust]

I can't do the math, I just know what I've experimented with.

With these tiny pager motors, it's not just speed control - it's torque.   Low torque means that motor control is really difficult as the motor at low speed is highly variable on rpm v. load, even if it can do full slip to the rail.   As I began to experiment with these little pager motor gearheads one of the phenomena I observed was that the motor load was much less and constant even if the locomotive load was all over, including going through curves, up and down grades, etc.  A Kato 11-105 motor with the Gizmoszone gearhead is just rock-steady on performance, literally a 'set it and forget it' and watch it climb a 4.5% grade at full slip and then down the other side and never make any audible difference on RPM or speed.  Without that, you're constantly jockeying the throttle to control speed.

The second thing I've played with is flywheels.   The Tomytec motors came with them, but on my diesel conversions they 'have to go' to make room for the same gearhead.  Comparing a stock motor with a flywheel vs. an 11-105 without a flywheel and with a gearhead isn't even close.   The gearhead is far more controllable, smooth, etc.   You'd think the flywheel would make a big difference, but to a certain extent, a higherer RPM armature seems to have some degree of kinetic energy sort of like a flywheel.   In my Climax kits, the ultra-tiny 3V pager motors on a high reduction work just fine  and are controllable with a small drop resistor in series - because the gearhead has much less variance in load to produce a full-slip condition.   Motor draw is negligible so a smaller resistor works.   On a direct drive they are pretty unsuccessful.   I've put tiny pager motors on Tomytec trucks for a successful 4-wheel powered truck, but it was completely uncontrollable pulling cars - motor barely had enough torque to spin the worm.

So the payoff is double - not just controllable speed but predictable performance under all load conditions.

[peteski]

So there isn't a compound gear below the worm?  I guess I've never noted that but also wouldn't have been looking at that detail to commit it to memory.  Just a simple clean and oil.  BUT I do have an older one here from my brother that needs maintenance that I just didn't get to yet.  And when I look at the bottom of the truck on a couple that I have, the final drive gears are offset to one side and that is usually the tell that there's a one piece, compound gear up in there.  Unless the worm is offset.   Next time I have one opened up I'll have to give that a closer look.  It sure would make a rocketship, even more than a 36:1 truck would.

Yes the older trucks (conventional low-friction design from all the manufacturers) do have compound worm gear with the larger gear meshing with the worm and smaller with the idlers.  Like you said, the final drive gears are offset. The trucks with integral worm have all gears centered.

[narrowminded]

Yes the older trucks (conventional low-friction design from all the manufacturers) do have compound worm gear with the larger gear meshing with the worm and smaller with the idlers.  Like you said, the final drive gears are offset. The trucks with integral worm have all gears centered.

Hmmm, I wonder what the thinking in that was.   Are all of the gears bevel cut, too?

[Chris333]

Just to add. Most of us all know how this Kato chassis runs. I put a Gizmozone gear head on it. The Gizmozone motor is the same size, but 3volts (I think) So I used the stock Kato motor.

[mmagliaro]

As you've all figure out buy now... there is no compound gear in the SD40-2 mid-production kato truck, so there is no more gear reduction.  It's 20:1.   

Gearheads are awesome because you get 4x (or 5x) the torque out of the motor.  That is so much overkill that a hill or some extra cars will not slow that motor down.  And likewise, coming down a hill will not remove enough load to matter either, so it won't speed up.   

It may be possible, however, to change out two gears in that truck with mod 0.2 compound types to get some reduction.

You can get module 0.2 gears in any bore, width, and number of teeth you can imagine from here:
https://shop.kkpmo.com/index.php

You can put any two you like on a shaft to make a compound type.  I know this is a pain to think about, but I really think that long-term, the "drivability" of this little thing is going to heavily depend on getting more gear reduction in there.

[JanesCustomTrain]

This one is also Kato, the Kato Centram comes with two of these. Bigger wheels, and dummy center wheels, and the proper sideframes ?

Jane

[peteski]

Hmmm, I wonder what the thinking in that was.   Are all of the gears bevel cut, too?

Um, not that I can tell. The gears (that also mesh with the worm) seem to be straight-cut. Unless the angle is so slight that it is not really noticeable.

The top gear meshes with the worm and with idler gears.

[narrowminded]

Um, not that I can tell. The gears (that also mesh with the worm) seem to be straight-cut. Unless the angle is so slight that it is not really noticeable.

The top gear meshes with the worm and with idler gears.

That surprises me.  I really wonder what the thinking was with that.    I trust they had a reason but offhand I can't think of one.

I have 6 or 8 Kato engines all with the offset final drive gear.  They aren't new.

[Atlanticflier]

WOW !  What an interesting thread.... My hat is off to all the creatives working this out. :

[dcutting]

I think I have a new solution for y'all. Instead of using a cannibalized Kato truck, we can use brand-new gears from existing tooling. I talked to Jason at Rapido and he said the he can supply the delrin gears from any of his models in bulk. In addition, he's also able to get the worms and wheels for me. This is really great! I'm thinking that the flexicoil truck from the FP9 will be a fine starting point, and then I can rearrange the gears to a flexicoil arrangement by changing the gear case dimensions. I can also move the worm down to the very end of the truck and give us some more room for the motor.

Motor-wise, I'm not so happy about throwing a gizmoszone motor in here because the worms that I am planning for won't fit those shafts. Making them fit will require an adapter. In addition, the 3V rating of the motor is a problem in my mind. I know you can get around it, but I would rather do it right. I really like the NWSL lineup of motors, and now with the ability to move the worm to any place inside the hood I think there's enough space for a motor that is 10mm on the flats, 12mm diameter, and 20mm long. That's without a gearhead, but the NWSL motors are purpose-made custom motors and from my testing they have a very good speed curve.  They use these things on the stanton drives in HO with only a worm. The FP9 also has a compound worm gear, so that should slow things down a bit as well. I can work on making a decoder that will fit in the limited space that we have.

I should add one more thing... the minimum quantities for turned stuff (the worm and wheels) is 1000 parts. I don't think this is an issue though... the wheel figure can be divided by six and the parts are probably cheap enough that having stock of worms wouldn't be a huge deal. Could always use them for other projects, and now that I have a source for gears I can make just about anything. This solution will make it so that the Kato stock of SD40-2 trucks doesn't die every time that they are released.

David

[randgust]

Something is horribly wrong with their specifications and drawings.

Checking on my Kato SD40-2 HTC truck with a ruler, the wheelbase of the truck from center end axle to center end axle is pretty much 14', a hair less.

The 'long end' toward the ear has a 7'3" wheelbase end axle to center and the 'short end' has a 6' 9" wheelbase.

Nothing there comes close to the stated 8'9 1/2" on the drawing, even the way they list it from the center axle to end axle.   The cab position is completely different from the actual one as well, get that, but I still figured that basic length and height would be correct, now I have no faith in that either.

They say it's not to scale but I at least expected the printed dimensions to be right somewhere.   I'm going to resize that side shot to the actual measured axle-to-axle wheelbase of the HT-C truck and take some more comparative measurements and see what I get, but if you're trying to scale one of these based on their figures, watch out.

On the remote chance that Kato blew it, I did find this from the EMD library:  http://utahrails.net/loconotes/EMD_HTC-Truck_ASME_72-RT-3_March-1972.pdf

End-to-end axle spacing is 13.96 feet; Kato got it dead on.  So although it LOOKS like an HT-C, either the measurements are completely wrong or it isn't.

[u18b]

By drawing.... I assume that you mean the one the company did.

Yes,  I agree... it's way off.

Though they put that this is not a scale drawing but for conversations- or something like that.


And yes,  there is something funky going on with their wheelbase measure.

I'm tied up with work for about another two weeks.
but I was planning on making a drawing--- though someone else may beat me to it.

Upon further study--- WOW!   There is another huge error.
The chart and the drawing don't match.





The drawing says from pilot face to pilot face is 27'  10"

But the chart says that is only the length of the body.

Contradiction.

[Missaberoad]

There is no Fuel tank on that drawing... perhaps it was an early concept before they built any...

The truck also looks like a Flexcoil not a HTC like on the production units...

[randgust]

It's not as precise as a tape measure - but when I resize the side photo so that the wheelbase measures just short of 14 feet, then the sill-to-sill length comes out to 31', and the railhead to cab roof comes out to 15' 6" (not the top of the AC unit).

FWIW the way I do this is to work in HO for scaled photos because it's more precise for measurement - then build in N.  So yeah, that pretty much confirms that those stated specs and dimensions are worthless.