Preamble

This article documents my investigation into how LEGO trains interact with curved tracks. Specifically, the relationship between bogie distance, bogie size, and the bogies' pivot radius.

"LDU" below refers to LDraw Units, where 1 LDU ≈ 0.4mm.

We start with bogies with three bogie sizes:

Small bogies' wheels are 60 LDUs (3 studs) apart.
Medium bogies' wheels are 100 LDUs (5 studs) apart.
Motor bogies' wheels are 120 LDUs (6 studs) apart.

Track sections

Just for reference. Only curved track is in scope for now. Curved tracks represent the tightest radius that a LEGO train would be expected to travel on.

Straight track. Nothing special here.
Curved track. Each segment is 22.5° radius.
4 segments make a quarter circle, 16 segments make up a circle.

Bogies on a curved track

At the same distance, they all seem to have the same rotation from their origin. In this experiment, different sized bogies are positioned with their pivot point 400 LDU apart, fit onto the track while rotated 14.2° from their origin.

Small bogies (60 LDU)
Medium bogies (100 LDU)
Motor bogies (120 LDU)

Different size trailers

At different distances, they have different rotations from their origin. In this experiment, identical 60 LDU bogies are positioned with their pivot points at different distances, which affects the rotation from their origin.

Spaced 200 LDU apart, rotated 7°.
Spaced 400 LDU apart, rotated 14.2°.
Spaced 480 LDU apart, rotated 17°.

With these datapoints, we can approximate the relationship as , where is the pivot point distance in LDUs, and is the bogie rotation. We can use this to evaluate different LEGO train bases.

If you have any feedback or questions related to this article, please reply to my post on Mastodon. This article is part of the LEGO set.