Help Constrain particles on axis

[Richard]

Sorry, but I don't fully understand the question.
If you're asking whether a transform has a "velocity" property, no it doesn't. A transform is composed of position, rotation and scale. No velocity or other physical attributes whatsoever.

Particles in Obi are not transforms either. They're just an index, that can be used to access their position, velocity, mass, etc. See:
http://obi.virtualmethodstudio.com/tutor...icles.html

I had to explain more. In the link you showed me has a code void Slide(Transform target, Vector3 railDirection) although the template is public static Vector3 Project(Vector3 vector, Vector3 onNormal);, and you said "Using Vector3.Project or Vector.ProjectOnPlane to constraint a velocity vector". So I asked that question.

I try to move some particle by transform, too. Obi's velocity is moved by vector?