N Scale EMD Model 40 critter build

[signalmaintainer]

@signalmaintainer, That would be something to see. Like the donkey patrol the Milwaukee did with SW1s in Minnesota.

Exactly what was in my mind!

[Jim Starbuck]

I needed to come up with a way to make the curved cutout at each corner of the hoods for the brake cylinders. Turns out it was quite simple. I glued bits of styrene to the inside corners of the hoods then used the mill  to cut the shape out of the solid blocks with an end cutter. They need a bit of cleanup but it worked nicely.

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[SP-Wolf]

Let's try this again -- sorry, for the miss fires




Best regards,
Wolf

[Jim Starbuck]

Very nice!
Thanks for your persistence Wolf

[Jim Starbuck]

There are lots of details to add but the shell is now one piece so I have a fixed target to start working the mechanism towards.

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[nkalanaga]

There's no reason yours couldn't be MU-capable.  Just because nobody else did it!

[Jim Starbuck]

Moving on to building the mechanism:

Axle spacing was accomplished by cutting a pair of axle cup pickups in two and sweat soldering them flush at the bottom to of carefully measured 1/8” brass angles.

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I’m using Tangent 36” wheels for a couple of reasons. They’re small enough to clear the bottom of the deck with only a .010” pocket milled in the underside of the deck but not protruding through. They’re also large enough to hold the axle tube gear high enough to clear switch frogs and grade crossings between the rails.
The angles needed a slight bit of relief to clear the wheels.

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The wheelsets will be cut to make half axles that slip into Kato geared axle tubes. There’s enough slack in the axle tube length to crowd the wheels together, slip them into the cups then open them up until they’re in gauge.

I superglued a wafer of .040 styrene to the underside of the angle rails to keep things square until the angles get epoxied to the underside of the deck after the wheel pockets are milled. Most of the crossmember will get cut out when milling the motor trough down from the top.

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[peteski]

Jim,
I wonder why not use Kato RDC wheelsets?  They are small (32" or 36") and the gear is also smaller to provide ample bottom clearance.  Or just use the axle tube with smaller gear from those wheelsets. The silver truck in this photo.

[Jim Starbuck]

Thanks Peteski,
That’s great to know about the RDC wheelsets. They look like a great resource that I will likely use on future builds.
I have some axle tubes with smaller diameter gears which I may end up using on the 40.
The biggest reason I’m using this approach is that I simply had the parts on hand. The motor will be a 7x16 double shaft coreless with a small diameter worm on each end driving each axle gear. The motor mount will be a simple slot milled down the centerline of the deck. I’ll widen the slot until the diameter of the motor “sinks” down far enough to make proper worm to axle gear engagement then soft mount the motor into the deck with Gallery Glass. I used this technique on the Davenport 45 tonner and it worked very well.
The slightly larger diameter axle gear that I’m using will keep the motor from having to protrude very far through the deck as I was saving the space between the axles for additional weight.
I’ve got the first geared axle built. I just tested it and the gear clears switches and even a Unitrack rerailer.

Jim

[peteski]

Thanks Peteski,
That’s great to know about the RDC wheelsets. They look like a great resource that I will likely use on future builds.
I have some axle tubes with smaller diameter gears which I may end up using on the 40.
The biggest reason I’m using this approach is that I simply had the parts on hand. The motor will be a 7x16 double shaft coreless with a small diameter worm on each end driving each axle gear. The motor mount will be a simple slot milled down the centerline of the deck. I’ll widen the slot until the diameter of the motor “sinks” down far enough to make proper worm to axle gear engagement then soft mount the motor into the deck with Gallery Glass. I used this technique on the Davenport 45 tonner and it worked very well.
The slightly larger diameter axle gear that I’m using will keep the motor from having to protrude very far through the deck as I was saving the space between the axles for additional weight.
I’ve got the first geared axle built. I just tested it and the gear clears switches and even a Unitrack retailer.

Jim

I'm glad I was able to provide  some additional info about part sources.    I believe the new Kato "critters" using coreless motors also have smaller gears on the axle tube, but those are finer pitch gears, so you would have to use another worm.  What is nice about Kato mechanisms, all the axles for various diameter drive wheels use 1mm half-axles, so the axle tube/gears and various diameter wheels can be mixed and matched.

As for clearance between the rails, every model *MUST* be designed not to have anything hanging lower than the top of the rail, or it will not run properly (through the turnouts).  That is not optional. So I'm not surprised that a rerailer is never higher than the top of the rail either.  Sounds like yours just squeaked by.   

How did you get the large diameter Tangent axles fit the 1mm hole in the axle tubes?  Did you turn the axles down to 1mm in a lathe?

[Jim Starbuck]

I’ve got a Kato 11-103 with the small gear axle tubes. Parting that out was going to be plan B if others didn’t work out. I’ve got a couple of the newer chassis with the coreless motors coming but again, using what’s on hand. Also the Kato worms use a 1.5mm shaft and my Bachmann worms are 1mm which go right on the 7x16 motor with no modifications.
Just going off my measurements it looks like the axle gear is traveling at .008”-.009” above the railhead so yes, it’s pretty much just squeaking by.
To make the Tangent axles fit the Kato geared tube I chuckled the tube in the lathe and drilled it out so the half axles were a nice press fit.

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I’m doing a fair bit of inventioneering with this build but so far everything is working out actually better than I had expected.
Here’s a photo of the motor with the worms.

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The ends of the motor body just clear the diameter of the gears when the worms engage the axles. I was concerned that I might have to use larger diameter worms to reach down from the center line of the motor shaft if the motor body interfered but although close it’s working just fine.

[Chris333]

Mo gear teeth mo gear ratio.

[Jim Starbuck]

The motor is mounted. The brass hold down screws are tapped through the brass angle and double as track pickup points. We’ll see how testing goes but I’ll likely abandon that and drill through the deck alongside the angle and solder the wires.
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[peteski]

Pretty clever Jim!

[Jim Starbuck]

I got the decoder and keep alive installed. There’s always more tweaking to do but I’m pretty happy with it so far.
Here’s a short video of the test run pushing Atlas 2 bays.