Ok. I have a ball at the very top and a long curved tube leading down and I want to turn the ball's physics animation into a follow path animation. In order to do that I need to somehow make a path out of all location points in which the ball was during its fall down the tube. But I don't know how to do it...
One method of converting a motion into a path is detailed in How to add trailing light effect to finger tips - by adding a particle system to drop particles as a vertex moves through space and then running a script to convert that particle system into a path. I also created an add-on as part of this answer to make the process easier.
The add-on can be downloaded from here : Particles To Path add-on
Once you've installed and enabled the add-on and you have your trail of particles (disable gravity and interactions from your particle system and have it emit a single particle for each frame of the animation) you simply execute the Particles to Path function (press Space (Blender 2.79) or F3 (Blender 2.8) and start typing the name) :
This should then generate the required path which you can use for your Follow Path constraint.
Using Btrace addon. (Which you can add in user preferences)
- In left sidebar in Create tab at the very bottom->In Btrace select "Mesh follow" option.
- Select "Verts" in there
- Select "Custom Select"
- Click on your object.
- Go to edit mode
- Select either a single verticle you want it to follow or add a new one inside the center of your object and leave it selected.
- Go back to object mode
- Click on OpenGl render animation button (it's somwhere above sync playback options at the bottom of the screen)
- After the animation is done press esc to go back to object mode.
- Select your object if it's not selected and press Run! button in Mesh Follow.
- You should have your curve there spawned.