Brass KMT Centipede Re-powering

[u18b]

Well, now that a certain company is coming out with a Centipede, I guess it was about time to finish mine.   

So this thread will show how I re-designed the power train and made this the locomotive Kumata SHOULD have made.



Now, other people have done this.  Todd Treaster made his run pretty well.  Ebit in Japan has done a wonderful job.  And Starman has a pair that run well.

So I decided to try it-- but with a catch.   Kumata traditionally uses a very typical design involving a gearbox.  This Centipede is the ONLY one they ever made in N scale that did not use that method.   So I an literally going to show how the designers at KMT should have done it.

I also need to add up front that this involved a good deal of scratch-building.  Something that is not my forte.  What you are going to see looks pretty ugly at times--- but hey, it works.

More info to come.

[u18b]

Generally speaking, the Kumata brass Centipede is a beautiful piece of crap.   The shell overall is wonderful.   But usually they run TERRIBLY.



If you are new to this locomotive, what makes it so different is that it has no frame.  Yep.  No frame--- at all.

The loco is in three sections.  Two powered trucks and one shell.   The shell is attached to the power assemblies by one bolster.

Getting at the screws is really tough.  It is hard to not scratch paint when doing so.



When you pull the shell, you get something like this.



There are some SERIOUS design flaws with this design.  Where shall I start.

The entire weight of the loco is held on the V shaped bolster under that drive shaft.
This is the stock configuration.  Notice there is a black plastic bushing UNDER the bolster.



This creates a rather high-boy look for this loco.



Here is a truck/power unit.
This is where the insanity resides.



You would think with 4 axles that this thing would pull walls down...... but only 2 axles are powered.
It gets worse.....



This is the key explanatory photo illustrating one truck.



In that photo the red circles are the powered axles.  The other two are idlers.

The bolster is at the big yellow X and blue arrow.

By now, you may be thinking.... WHAT?!   They placed the balance point of that truck BEHIND the driven axles?   That would mean part of the weight is on the idlers.

And you would be correct.  Great big brass Centipedes have terrible traction.

Another problem I have come to understand better having worked extensively with brass EP-2s is that DOUBLE motor locomotives does not automatically mean double power.  Sometimes is means 50% power.

That is because unless the motors are matched PERFECTLY, they will work against each other and performance will go down (and noise will go up.).

So, my plan is.....

1.  Redesign this with a FRAME and gearboxes.
2.  Put the weight 100% over the DRIVEN axles.
3.  Repower with one really good motor.

[u18b]

The shell is a self-contained unit.  I wonder if a custom frame would fit over that hole.



The driven axles are centered under the worms.  So that is where my gearboxes need to go.



I made a paper template and drew the pattern out on a sheet of brass.



A lot of work with a motor tool and files.
That's more like it.

[u18b]

Now comes the hard part.  Dealing with the truck.



Remove the bolster screw and the two screw that hold the motor/worm contraption.

Now I need a sheet of brass to go in that spot with a hole for the gear.



Looks good.



That is the base.  Now for a geartower.
Square brass tubing.



Flux the original (square) tip.


Add some solder to pre-tin since brass is a heat sink.

[u18b]

Lay the brass base on some wood for soldering.



Now heat the joint keeping it all as square as possible.
And yes... this is a STAGED photo.  LOL.  I'm not holding a hot solder tip.  I was too lazy to edit and crop.



Another staged photo.  You can see I'm not perfectly centered.
Heat and try again.


OK, that's better.

[u18b]

Here is a check on squareness.



Now I need an idea where to drill the hole for the gear shaft.  That is an old Kato/Atlas U25B gear.  Perfect match for the brass gear.



OK.  That looks like a safe height to cut.




I made a mark and measured my height for the shaft.

[u18b]

Holes drilled in the base.
Shaft and gear mounted.
Gear tower mounted.
progress.   Now to do it again for the other truck.



Notice the balance point of this truck is now where it SHOULD be--- between the two driven axles.

[pnolan48]

Oh man, I can't wait to see what this sow's ear turns into. You got me chuckling, Ron. Neat work, and neat attitude about it.

[u18b]

Pete,

you haven't seen anything yet.

Ugliness comes next.   

[u18b]

Here is a typical Kumtata chassis.
Two gearboxes and pins that hold the trucks in as well as transmit electricity.




Actually, in all but two, the chassis does not use pins, but rather headless screws.



That thing is great.
Unfortunately, I did not know how to get one to work with this.

Consequently, my push pin/shaft was a little loose.
So I added some globs of solder to give the wall more thickness.


 

[u18b]

Now, as you can see, the geartower is rectangle.  But we need it round to pivot.

So back to the brass.




I cut a few arcs.....



And then solder them to the geartower.
It's pretty ugly, but it works.

[u18b]

I took the gearboxes out of one of my other KMT locos.  Time to mount them to my new frame.



Styrene shims help get the height correct.



The screws were cut off even with the bottom of the frame since they can cause shorting with the trucks.



Here is a trick I discovered for making Kumata locos run better.
The trucks are charged to opposite polarity. 
And the frame is usually charged to one of the trucks.
Thus a problem occurs if the opposing truck touches the frame.

So the solution is to place some clear packing tape across the bottom of the frame.

[Ed Kapuscinski]

Ron, you're a maniac. It's awesome.

[u18b]

I got the loco running (more in a moment), but I hated crippling my brass Trainmaster by robbing it of it's gearboxes.  I wanted that Trainmaster back to running.

So I set about to try and make more gearboxes.  This would help with future repairs of KMT locos..

I was going to make a mold and then castings.
The base of the gearbox was VERY thin, so I fattened up my master with styrene.
I have a coulple of different gearboxes to use.


I made RTV molds.



I then took some old Walthers Temp-Lo and tried to make a metal casting.
I obviously don't know what I'm doing when casting metal.
Hopefully, I'll get better with time.
But for now, this was a bust.




So I decided to regroup and go with plastic gearboxes.  This would require hot wiring the truck with jumper wires.

[u18b]

I made plenty of castings with Alumilite.

They worked well.

I then had to add the brass wall to retain the pin--- it kept sliding out.




That is a Kato worm.  Shorter, but same threads and diameter.  I added washers as spacers.



To power this locomotive I picked about the biggest, baddest, high quality motor I could find.
This is the beast that Life Like placed in the E6 locos with plastic frame.  Flywheels are massive.
Powerful 5-pole skew wound motor.

The u-joints are the very ancient joints from a 1980s era Atlas/Kato RS-3.