Generate smoke when mesh gets hit/moved

Can we have an option for mesh to produce smoke (brush/inject) when it starts moving (animation keys or gets hit by other mesh)
In the image attached you can see train going backwards and hitting rocks. All rocks start producing smoke even the ones that are not hit yet making it unnatural.

I know you can have multiple PHX sources but then you have to manually time when each rock gets hit to produce smoke.

thank you

You can use the discharge modifiers and base them on Speed. So when the emitter object meets a certain speed threshold it will start emitting.

You can take a look how this works - here https://docs.chaosgroup.com/display/PHX3MAX/Discharge+Modifiers

Thank you

By the way is there anyway to have a sample scene or add changes to the attached scene. Our goal is to discharge only when rocks are hit. We still cannot do it Thank you
2014 12345.zip (1.54 MB)

Just select the first point for the Speed modifier and set it to 50 and 0. This means that everything that has a speed below 50 will emit nothing.

Additionally, you could complement the discharge modifier by speed with a v-ray distance tex, plugging it as a map for the smoke discharge, e.g.