Help Constrain particles on axis

[josemendez]

Sorry, but I could not realize well. The reference states how to change the direction, not to constrain. Or is there another way?

Constraining an object so that it moves in a certain direction is equivalent to projecting its velocity vector to that direction, which you can do using that function.

In the link I provided, there's an example that constrains a rail-mounted gun so that it only moves along the rail direction. You can do the same for particles, so that they only move in a given axis.