Animate Locomotive by follow Path

Question

I want my locomotive to follow rails over a hill. The loc should always be on the rails. I've tried a few things (such as https://www.youtube.com/watch?v=OruVKMGGPX8), but I always come back to the same problem: the locomotive follows the rail, but leans into the curve:

How can I fix this?

Answer 1

If your curve is flat you can simply change the curve type to 2D to ignore the tilt for each control point:

If it is 3D and you want to keep it that way, you need to reset the tilt of each control point that isn't set to 0 degrees:

EDIT: You can also try setting the Twist Method to Z-Up.

EDIT 2 (after seeing the blend file):

Start with applying all transform on the curve (CTRL + A > All Transforms), then set the Twist Method on the curve to Z-Up. Then you'll have to tweak the Z-rotation of the locomotive to make it line up with the track, something like -28 degrees seemed to do the trick for me.

Answer 2

if you delete your path constraint and if you use a bone and use follow path constraint like this:

and apply scale + rotation for curve + locomotive and use edit mode to place the locomotive exact on the rails, you will get this:

Answer 3

I couldn't find anything on automatically aligning curve tilt to +Z, so you would need to use a complex geonodes setup, then, because apparently the constraint isn't affected by geonodes, you would need to capture the calculated tilt as attribute, make Python read the evaluated attribute and write it to the original geometry (and you would need to run the Python script after each modification of the curve)…

Or you could just align your object up using Geometry Nodes:

1. Clear all rotations on your loco.
2. Change Forward Axis of your tracking to $-x$, because that's the direction your loco looks at when you duplicate it and ⎇ AltP clear parent:
3. Add Geonodes setup to your loco:

Of course you could animate it all in geonodes to begin with: