Best Of The TP56/TP70 Kitbash thread N scale

[u18b]

David,

That picture is not showing for me.

Did you set the sharing options on the folder?

[bman]

Would a coreless motor work in this instance?  Just wondering as I have zero experience in electric motors, gear boxes and such. I know the Hornby SW I have runs very well and I believe it uses one.  I happen to have one of the Kato trucks sitting in my parts box.  How it got there I've no idea.  And I need yet something else to finish halfway on my modeling table.  But one of these would be fun to mess with for a small portable switching layout.

[chessie system fan]

What would happen if you flipped the worm around?  If it works that helps this motor option.

[u18b]

What would happen if you flipped the worm around?  If it works that helps this motor option.

I already thought of that and looked at it.

But I don't think anything is gained.  It just pushes the motor further out.

[mmagliaro]

Would a coreless motor work in this instance?  Just wondering as I have zero experience in electric motors, gear boxes and such. I know the Hornby SW I have runs very well and I believe it uses one.  I happen to have one of the Kato trucks sitting in my parts box.  How it got there I've no idea.  And I need yet something else to finish halfway on my modeling table.  But one of these would be fun to mess with for a small portable switching layout.

Probably not, for two reasons.
1.  They are not meant to carry the bearings loads of a worm (unless you pay for a real coreless, like a Maxon or Faulhaber) so the worm would have to go in its own bearings and be joined to the motor shaft by a U-joint, and there isn't much room for all this.
2. They aren't usually short enough.  Even the tiny 8mm ones are 16mm long, but I wouldn't use those without more gear reduction than you have here.

[Chris333]

If you go ahead and make a chassis I suggest at least a 70: gear ratio or even higher. So you can actually use the this when your done.

[Mark5]

I'm not much for critters, but this one I love! Hope you can pull this one off!

[wazzou]

If you go ahead and make a chassis I suggest at least a 70: gear ratio or even higher. So you can actually use the this when your done.

Yeah, getting it to move under it's own power is cool and all but having some functionality is altogether different and better.

[mmagliaro]

If you go ahead and make a chassis I suggest at least a 70: gear ratio or even higher. So you can actually use the this when your done.

Right.  And that truck is only 20:1  (I know because that truck has a mod 0.2 geared axle with 20 teeth which just so happens to be the exact gear tube I am using in my 0-6-0 project).  20:1 is going to be a tough task to make it run with any kind of low speed.
How does the SD40-2 get more reduction in it?  I only have the truck, not the whole engine.  Is there another reduction somewhere between the motor and the truck?

[peteski]

How does the SD40-2 get more reduction in it?  I only have the truck, not the whole engine.  Is there another reduction somewhere between the motor and the truck?

Um, the motor shaft is directly coupled to the worm shaft.  No additional reduction there.

[mmagliaro]

Um, the motor shaft is directly coupled to the worm shaft.  No additional reduction there.

Yeah, I know, I was just thinking there had to be *something* to reduce it more.  20:1 is more like
the old Rivarossi/Trix days.
Does the SD40-2 mid production run like a rocket ship at 12 volts?

[narrowminded]

Expect a compound reduction in the assembly.  Probably one compound gear mating to the worm (a big gear and a smaller one, one piece, turning in unison).  Count the large gear that mates to the worm and that number will be the primary reduction (x:1).  Then count the teeth on the smaller gear on that compound gear.  Then count the final drive gear teeth (the gear on the axle).  The ratio between the smaller gear on the compound gear to the axle gear is the secondary reduction.  Primary x secondary equals the full reduction between motor and wheels. 

The intermediate gears are idlers and as such, strictly place holders, space fillers, to transmit the power where needed but have no effect on the ratio.   They do reverse the shaft rotation so are often required, even if not for axle C/L distance, then to change the rotation so both axles are turning in the same direction.  Expect one or three or... always an odd number between final drives to maintain direction.

[narrowminded]

For a reference, the 44" w'base prototype in my video from a few weeks ago is running 125:1 drive ratio.  Expect somewhere around 35:1 or 45:1 in a typical truck.  That would explain the wild MPH in Ron's video.  It is a problem getting the desired reduction while keeping the device small.  There just isn't room for the necessary hardware.  Also, my unit at 125:1 was with 24" wheels.  If these trucks have 36", 40", or more then the speed is further increased by that factor.  For comparison, that's a speed increase of 50% for a 36" wheelset or 75% for a 42" set, just from the wheel diameter. 

What starts to become evident is what Randy has done with his planetary conversion and why it works well.  It's an additional 5:1 ratio going in.  If you have a 36:1 in the truck and then add 5:1 on the input it goes to 180:1 (5x36).  Back to the larger wheels that add speed back and you settle in to a pretty well balanced final drive ratio, wheel factor included, as he has discovered.  Pretty compact but at the small sizes you're looking for, that too adds a fair amount in length and maybe diameter.

One of the reasons the gearing has to be so low is the smaller motors typically spin a lot faster, getting their power from RPM.  The ones I'm using are up in the 25 - 30,000 rpm range so to get them to an appropriate speed and also to be able to do some work you need the big gear reductions.  The motor you were showing probably isn't that fast but it's likely still way up there when compared to an Atlas low speed, also much larger, motor.  Hope that helps with understanding the issue.

[peteski]

Yeah, I know, I was just thinking there had to be *something* to reduce it more.  20:1 is more like
the old Rivarossi/Trix days.
Does the SD40-2 mid production run like a rocket ship at 12 volts?

All Kato locos are rocketships at full throttle. They have been since day 1. That is one of the negative things about Katp models (and unlike Atlas with their slower motor) they don;'t seem to want to change their design.  What mitigates this a bit is that with with their very low-friction mechanism the locos run slow and smoothly under very low voltages. Plus DCC mitigates the problem too (with being able to restrict the top speed).

The 6-wheel trucks with integral worm do not have a secondary gear reduction. Surprisingly the same worm gear which engages the worm also meshes with the idlers.  Usually worm gears have different tooth geometry from the other (plain straight-cut) gears in the truck

[narrowminded]

The 6-wheel trucks with integral worm do not have a secondary gear reduction. Surprisingly the same worm gear which engages the worm also meshes with the idlers.  Usually worm gears have different tooth geometry from the other (plain straight-cut) gears in the truck

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.