[MoC] TP56 Industrial Switcher Locomotive

[jtlan]

Want an SD40, but can't afford one? Here's a half-off deal for you:

...literally. These little locomotives are made by cutting an SD40 in half, attaching the frame to the truck, and installing a new and efficient prime mover and cab. I kid you not:

Link to the manufacturer's website.

I went about building this model the same way I usually do: Gather reference images, find an engineering drawing, and overlay grid paper over the scaling drawing. Complicating the matter was that the diagram in Tractive Power's specifications brochure was very obviously wrong -- there's no way the SD40 truck is that long! Comparing the drawing to photos of the real locomotive confirmed my suspicions. I overlaid a drawing of an SD40 truck on the diagram of the body, and worked from that.

As with my Standard Class 2, I selectively compressed the wheelbase to make the axle-to-axle distance a whole number. This made building the truck frames much easier:

After working out the frames, I worked on designing a drive train that would power all three wheels (once again, I picked a small prototype, which didn't help). Here's what I came up with:

That's the ungeared 9V motor driving a shaft with a belt, powering all three axles with worms. The center axle slides to traverse curves:

As a side bonus, I get to check another motor off my list of "motors to power a locomotive with". Because of the belt drive, unlike any of my other locomotives this locomotive's pulling power is limited by torque instead of weight (because the belt will slip first). It still has plenty of pulling power for something of its size. The locomotive traverses almost all track arrangements -- strangely, it will skip switches coming out of a curve, but only in one direction.

The hood hides the battery box. One section isn't held on by anything, and comes off to reveal the power button:

The other sections are only connected with one stud (and some interesting panel spacing to grab the power connector), making it easy to change the batteries.

The receiver sits on top of the motor in the cab and receives signals through a hole in the roof. Unlike the other locomotives I've built, this one has great reception from all angles.

I really wanted to build this locomotive in Curry Rail colors, but the parts I needed weren't available in either teal (too old) or bright green (too new?). So I built it in black, but left the frames grey to show the details better.

Thanks for reading! Full Brickshelf gallery, pending moderation.

[Feuer Zug]

Very cool little switcher. Good use for an old SD40 frame. You MOC looks great and I love the way you powered it.

[JopieK]

Very nice indeed! Better not really cut it in the LEGO version though ;) I like also your solution for the yellow markings incorporating them with the railing.

[ColletArrow]

Very nice little loco! For the central axle, you could have used 11955 (8-tooth gear without friction) to prevent any skipping that I suspect may be caused by the sliding central axle as the gear becomes unaligned. Just like the company's apparent motto, it's simple and it works.

[zephyr1934]

That thing is brilliant in so many ways. The way you were able to get so much mechanical in such a small package is unbelievable in its own right. But I must say I am particularly fond of the cab, brilliant solution to get all of those windows in there.

[McWaffel]

I like this new trend of people cramming power functions into tiny engines. Super satisfying to see this happening 

Great work on the drive train! Would love to see it in action

[legoman666]

Very nicely done. Love the side cab windows, the front ones look a little too tall though. Nice detailing on the trucks. My 7 wide sd40s have the same wheel spacing and also do not go through switches. 

[jtlan]

2 hours ago, ColletArrow said:

Very nice little loco! For the central axle, you could have used 11955 (8-tooth gear without friction) to prevent any skipping that I suspect may be caused by the sliding central axle as the gear becomes unaligned. Just like the company's apparent motto, it's simple and it works.

Thanks, ColletArrow! I tried using the sliding gear, but the extra half-beams required to center the gear added extra friction, so I went with this design. The axle doesn't slide very far (5.5 axle in a 6-wide space), so the gear doesn't actually disengage from the worm.

 

14 minutes ago, legoman666 said:

Very nicely done. Love the side cab windows, the front ones look a little too tall though. Nice detailing on the trucks. My 7 wide sd40s have the same wheel spacing and also do not go through switches. 

Thank you, Legoman. I think the issue with the center windows is that they're slightly too far up (due to the thick sill at the bottom of the window piece).

The locomotive goes through switches just fine, except when coming out of a curve into a switch that's also set to turn the same way:

... and even then, it only happens with one orientation of the locomotive. I've had success with the same wheel arrangement in unpowered rolling stock, so it must be something about the dynamics of the transmission.

 

52 minutes ago, McWaffel said:

I like this new trend of people cramming power functions into tiny engines. Super satisfying to see this happening 

Great work on the drive train! Would love to see it in action

Thanks McWaffel! I enjoy the challenge of building compact mechanisms into small locomotives.

The weather's been poor here so I haven't had a chance to take footage (the photos were taken in a small dry spot on the porch).

 

1 hour ago, zephyr1934 said:

That thing is brilliant in so many ways. The way you were able to get so much mechanical in such a small package is unbelievable in its own right. But I must say I am particularly fond of the cab, brilliant solution to get all of those windows in there.

Thank you, Zephyr. The "1 plate thick corner pillar" is an ever-present challenge when modeling diesels. I'm pretty happy with the wrap-around solution I came up with using the small panels.

Edited March 5, 2017 by jtlan

[M_slug357]

@jtlan, It didn't occur to me before, but would the addition of a 2nd belt help with the transmission of power? Also, what do you think about applying something to the pulley wheels to make them more... grippy?

Lastly, you mentioned your loco's been jumping the switches, but is this happening on 9V or PF switches? My lighter engines always jump 9V switches in similar setups to the one you illustrated.

 

Anyways, can't wait for your next loco!

Edited March 5, 2017 by M_slug357
grammar fails

[jtlan]

22 minutes ago, M_slug357 said:

@jtlan, It didn't occur to me before, but would the addition of a 2nd belt help with the transmission of power? Also, what do you think about applying something to the pulley wheels to make them more... grippy?

Lastly, you mentioned your loco's been jumping the switches, but is this happening on 9V or PF switches? My lighter engines always jump 9V switches in similar setups to the one you illustrated.

 

Anyways, can't wait for your next loco!

Unfortunately, due to a half-stud offset there's only room for one belt. I would get a bit more torque if I could find a thinner pulley for the worm shaft (the belt would be wedged in to the groove, increasing friction), but I'm reasonably happy with how the locomotive drives now. I haven't tried pulling anything too heavy, but at the BayLUG Holiday Show it was able to rescue my Standard Class 2 and a short string of 2-axle cars.

Good point on the switches -- I've only tested with 9V, and I know that the geometry of the guides is slightly different on PF tracks. The locomotive isn't that light, so it's not so much that it derails as it ... ignores the switch and goes straight instead.

[Beck]

Love it! It seems you have become very skilled at making peculiar compact powered locomotives. For the central axle you could have used this part, which is designed to have the axle slide through it.

My response to the designer of this loco:

 

Edited March 6, 2017 by Beck

[M_slug357]

 

@jtlan, that sliding 8-tooth gear might be useful if doubled up on that central axle? That way the axle can still slide w/o the gears losing contact with the worm.

Also if the engine is ignoring the switch toggle, maybe add a "bumper" of sorts between the curve and the switch?

[dr_spock]

Very nice.   It seems like there is a prototype for everything.  Plasma cutting torch is a handy dandy tool. 

 

[CrispyBassist]

I've had similar issues with the wheels of my 6-axle heavyweight coach catching on 9v switches, and I realized it was because the PF ones have a small indent on the straight rail that the tip of the switch can fit into. The 9v ones don't have this because of the metal part, and so there's a small bump where a wheel flange can catch. The long wheelbase of this lil guy (11 studs, by my count) means the wheel flanges are coming in at a tight angle in that configuration, probably just enough to catch the switch. I changed the trucks such that one of the end axles slid, rather than the middle. That took care of it completely!

 

Nice job cramming all the PF components into such a small package! And the light grey truck really does make the details pop.

[LEGO Train 12 Volts]

Very nice micro technology  ...how much is fast, and how many wagons can pull?

I love the beautiful design of your cab!

[Man with a hat]

Oh wow. Very nice. Not only about being able to put all the PF in it, but the detailing is great as well. Like your solution for the windows

[jtlan]

On 3/5/2017 at 8:38 AM, McWaffel said:

I like this new trend of people cramming power functions into tiny engines. Super satisfying to see this happening 

Great work on the drive train! Would love to see it in action

On 3/6/2017 at 1:14 PM, LEGO Train 12 Volts said:

Very nice micro technology  ...how much is fast, and how many wagons can pull?

I love the beautiful design of your cab!

Here's some footage I took of the locomotive moving some gondolas and pulling two Umbauwagen, to give you a sense of what it can do.

Does anyone know how to embed video with the new posting tools?

[ColletArrow]

Just copy and paste the URL into the text, the text turns into a video automatically!

It's a beautiful little runner, as well. I can't get enough of it!

Edited March 12, 2017 by ColletArrow
Added comment

[jtlan]

10 hours ago, ColletArrow said:

Just copy and paste the URL into the text, the text turns into a video automatically!

It's a beautiful little runner, as well. I can't get enough of it!

Thanks. That's so undiscoverable...

[baard]

Nice execution to this shunter. I like the use of a rubber band to make it run.

Thanks for the video!