One thing that I find myself using quite a lot these days is particles in After Effects.  In a lot of cases, I am having some kind of particle flying around the screen and/or interacting with an element in one of my comps.  I used to do things in what I call the "painful" way, which was to use the particle effects "position" cross hairs to create a path for the particle to fly around on, and I always ended up with the same result.  A very linear, boring path that seemed fake, as for me, I like to have my particles move in a smooth, realistic way, oh and did I mention that I also want them to be easy to create as well?  Well, that's where Motion Sketch comes into play.  Motion Sketch is hidden away in the "WINDOW" drop down menu, and is a tool that is so often overlooked, but creates great results.  Let's see how it works.  I'm going to create a particle that moves from the left side of the screen to the center, does a circle, and then moves to the right, and I'm going to create it in about twenty seconds flat.

To begin, let's create a layer that will have our particle on it and we're going to use an adjustment layer, and for an effect I'm going to use Trapcode Particular's Firestarter preset.  One thing to remember about Particular's presets is that once you apply them, they will automatically apply keyframes to the particle to have it move, so we're just going to delete those keyframes so that we can create our own path.  Once you have deleted your keyframe, take the "Position XY" target, located under the "Emitter" section of Particular, and pick a point anywhere in the middle of the screen, click on it, and add a keyframe for later use.  Press "0" on your number pad to preview the effect, and what you should see is the particle effect appear, and stay static, like it does below.

Next, navigate your way to WINDOWS>MOTION SKETCH, and once you let go of the mouse, you will immediately see the motion sketch window appear to the right side of your Comp window.  You can see two adjustable parameters in Motion Sketch, one being "Capture Speed at" and "Smoothing".  For what we are creating, we will leave the "Capture Speed at" at 100%, and we are going to adjust the "Smoothing" parameter to 6, which should give us a pretty smooth looking path for our fire to flow around.  We're ready to sketch.

Once we click "Start Capture" at the bottom of the window, After Effects is going to start recording the movement of your mouse to create a path to animate your particle on.  The recording starts when you click your mouse anywhere in your comp, and stops recording once you let your mouse go.

I want our animation to be ten seconds long, but when I'm sketching the movement I want, the time is actually irrelevant.  Take a look at the video below to see me sketching my path in real time.

Insert Motion Sketch in Action.mov Here

Once I let go of my mouse button, the sketching immediately stops and I see that I now have position keyframes on my adjustment layer.  Now, as I said before, when sketching, the time is really irrelevant, as it can be easily adjusted after the fact.  Now, as you can see from the keyframes in the below image, my animation goes to about the seven second mark, but I really want it to go to the ten second mark, but I want to make sure that when I'm extending everything, that the keyframes move relative to each other to keep the exact same look and feel that I have in my seven second animation.

This is done quite easily.  First, select all your position keyframes by clicking on "Position" under "Source Name" in your timeline.  Doing this selects all the keyframes for that particular parameter.  Next, press "Option" on the Mac or "Alt" on Windows, and drag the last keyframe of the animation down to the ten second mark.

As you will see, the first keyframe stays stationary, and all the other ones move proportionately to each other.  Now that I have my timeline ten seconds long, it's time to add our particle generator to our path.  As you can see, if you hit "0" on the keypad to preview what we have so far, you will see the adjustment layer go spinning around the screen with a stationary particle effect that just looks wrong in every possible way.

Here's how we fix that.  First, click on "Position" again to select all the position keyframes for the position of the adjustment layer, since those parameters are what we want our particle to move around to, and press "CMD+C" (CNTL+C on Windows) to copy all the position keyframes.

Next, select your "Particular" effect and press the "U" key so we can see the "Position XY" parameter.  We added the keyframe earlier so that you could quickly find "Position XY" for us to adjust now.  I would recommend deleting that one keyframe you added earlier, because you don't need it anymore.

Next, click on "Position XY" under "Source Name", so that we are only effecting that parameter, and press "CMD+V" (CTL+V on Windows) to paste our position keyframes from our adjustment layer onto our "Position XY" parameter.  We're almost done.

Next, click on "Position" under "Source Name" again to select all the position keyframes of your adjustment layer, and press "Delete" to remove them.  Finally, right click on "Position" under "Source Name", and click on "Reset" to put the position back to its default.

Now click "0" to preview your timeline.  Your Particular particle now travels along the "sketch" you made with Motion Sketch, and it looks quite "organic" and lifelike.

If there is anything you would like to know about After Effects or motion graphics in general, feel free to drop me a line at kevin@reelclever.com, and maybe your question will be the topic of my next article.