Quick questions regarding motorization...

[LMGbros 772]

Hello everyone, I am currently designing a LEGO model of a New York Central J3a streamlined Hudson. It will use Brick Train Depot 3D-printed XXL disk drivers, and I intend to power it with two Power Functions L Motors connected to the center axle. Where I am getting stuck is 1: How to mount the motors inside the boiler, and 2: how to make the locomotive fast and powerful, strong enough to pull at least 5 coaches. (Specifically, the ones that Anthony Sava has for sale on the Brick Train Depot website, that are equipped with roller bearings. I bought them some time ago, and I wanted to make a Hudson to go with them. 

I'm pretty new to designing and building my own LEGO locomotives from scratch. I've made a few smaller engines before, but nothing this large with this motor set up before, Any assistance or advice you can provide will be much appreciated. Thank you. 

[zephyr1934]

welcome @LMGbros 772

Books could be written about building lego steam engines, but here are some good starting points.

If you've built the cars already, that will help you design a suitable drive-train for the locomotive, otherwise, try to find some cars that will mimic the load of the train you want to build.

Next up, forget about the "look" of the locomotive you want to build. Start by getting the mechanicals worked out. So wheels (drivers, pilot and trailing), motors, and gearing. Forget about rods, boiler, or anything else right now. Though you will want to put some weight on the drivers. Either use boat weights or roll of coins, or simply extra lego bricks.

Now build and test until you have a unit that can pull what you want the way you want it. Run into problems along the way? Post pictures and questions on EB.

Potential point of problems: if the train wheels do not have traction bands you might have difficulty pulling a heavy train.

Once you get that worked out, then establish your clearances. Project your locomotive into the "ground" and map that shape out with plates and just enough bricks. Then put that shape on your tender trucks and locomotive trucks. Will it travel through all the curves and switches you need it to? Forward and back? What about bumpy track, do you anticipate bumps? If so, simulate that in your testing.

Once you've past that, time to figure out the rods and cylinders. Get past that and then comes the time to try to squeeze everything inside the size of the boiler.

 

[LMGbros 772]

On 4/4/2025 at 5:14 PM, zephyr1934 said:

welcome @LMGbros 772

Books could be written about building lego steam engines, but here are some good starting points.

If you've built the cars already, that will help you design a suitable drive-train for the locomotive, otherwise, try to find some cars that will mimic the load of the train you want to build.

Next up, forget about the "look" of the locomotive you want to build. Start by getting the mechanicals worked out. So wheels (drivers, pilot and trailing), motors, and gearing. Forget about rods, boiler, or anything else right now. Though you will want to put some weight on the drivers. Either use boat weights or roll of coins, or simply extra lego bricks.

Now build and test until you have a unit that can pull what you want the way you want it. Run into problems along the way? Post pictures and questions on EB.

Potential point of problems: if the train wheels do not have traction bands you might have difficulty pulling a heavy train.

Once you get that worked out, then establish your clearances. Project your locomotive into the "ground" and map that shape out with plates and just enough bricks. Then put that shape on your tender trucks and locomotive trucks. Will it travel through all the curves and switches you need it to? Forward and back? What about bumpy track, do you anticipate bumps? If so, simulate that in your testing.

Once you've past that, time to figure out the rods and cylinders. Get past that and then comes the time to try to squeeze everything inside the size of the boiler.

 

Thank you for the reply, zephyr. I have not yet built the cars just yet, but I do have the parts for the observation car. 

You have provided an excellent guide, and I thank you for that. I intend to use it during my development of future train mocs. I haven't tried to build the drive train IRL yet because I don't have the parts for it, (especially the wheels) but I hope to soon. 

I do intend to post photos and ask questions if I run into trouble, but when I tried to post a photo of one of my mocs in another thread a few weeks back, I could not upload it because of the file size limit. I know this forum is not an image hosting website, but I'll have to find a way to lower their size below 100 kg so I can post them. 

Thank you again for your assistance. 

Edited April 6 by LMGbros 772

[Murdoch17]

1 hour ago, LMGbros 772 said:

Thank you for the reply, zephyr. I have not yet built the cars just yet, but I do have the parts for the observation car. 

You have provided an excellent guide, and I thank you for that. I intend to use it during my development of future train mocs. I haven't tried to build the drive train IRL yet because I don't have the parts for it, (especially the wheels) but I hope to soon. 

I do intend to post photos and ask questions if I run into trouble, but when I tried to post a photo of one of my mocs in another thread a few weeks back, I could not upload it because of the file size limit. I know this forum is not an image hosting website, but I'll have to find a way to lower their size below 100 kg so I can post them. 

Thank you again for your assistance. 

Sadly, You can't post photos directly. The space provided is for your avatar and signature. You're gonna need to find another site to host the photos, then post them here.

Edited April 5 by Murdoch17

[LMGbros 772]

9 hours ago, Murdoch17 said:

Sadly, You can't post photos directly. The space provided is for your avatar and signature. You're gonna need to find another site to host the photos, then post them here.

Here is a photo of what I have so far. It is from a discord server I am in that is dedicated to LEGO train building. 

[zephyr1934]

10 hours ago, LMGbros 772 said:

Here is a photo of what I have so far.

Your side rods have a pair of 7 long half beams connected at a single stud at the middle driver. That might allow too much flex (or it might not) so something to test when you build it in real life. If it does prove problematic, you can probably fix it by moving the outside 7 long half beam forward one stud. Of course I can't help but recommending using a single 13 long rod instead (grin). In all seriousness though, using a non-lego part for the 13 long side rod will allow you to prototypically connect to the middle driver while moving the cylinders in 1/2 stud each.

 

[LMGbros 772]

14 minutes ago, zephyr1934 said:

Your side rods have a pair of 7 long half beams connected at a single stud at the middle driver. That might allow too much flex (or it might not) so something to test when you build it in real life. If it does prove problematic, you can probably fix it by moving the outside 7 long half beam forward one stud. Of course I can't help but recommending using a single 13 long rod instead (grin). In all seriousness though, using a non-lego part for the 13 long side rod will allow you to prototypically connect to the middle driver while moving the cylinders in 1/2 stud each.

 

Thank you for the feedback. Those technic beams are stand-ins for a 13 L side rod I intend to acquire when I eventually build the J3a with actual bricks. The technic beams are tolerable, but they just don’t look the proper part for steam locomotive builds. 

[LMGbros 772]

 

Current progress on my J3a for the day. I have the drive train figured out, so my next step is to mount the motors more sturdily, and then build the rest of the engine around the motors. Before that, I intend to attach the front and read trucks to the main locomotive frame. 

 

Also wanted feedback on the rear trailing bogie. Is this a good design or should I modify it?

[LMGbros 772]

Update:

 

So after just over a week of work, I have begun to build the body around the motors. However, I realized that I didn't take into account the length of the motor cables for the forward motor. Would it be a good idea to move both motors inward one stud? I'm currently leaning toward that option. Doing so would also eliminate the 1x7 technic lift arms from the design. 

Hypothetically, if I were to drop down from two motors to one, would the Hudson still be able to pull at least five coaches at a reasonable speed?