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Set a Motorcycle Tire on Fire and Create a Fire Trail

Forum|Forum|2 years ago
July 21, 2023
3 replies
685 views

Hi folks,

A week ago I posted a thread seeking help for a music video project. I’ve dealt with the problem I had, but now I’m facing other challenges that I can’t seem to find the best way to execute.

The scene I’m sharing below for download is the closing one of the video and my idea is to lit the back tire on fire that would also leave a fire trail after it, as my motorcycle rides on, very similar to Ghost Rider when he rides a motorcycle.

1 – Regarding setting the tire on fire - I tried camera tracking and creating a null and a solid which I masked to the tire shape and place the fire asset in its place, but it didn’t work. I also tracked the motion of the tire/motorcycle with Mocha (unfortunately, I’m with Mocha 2020 and don’t have the Power Mesh option), exported the tracked data to a Null and assigned a pre-comped layer with the fire assets, but didn’t work. I also tried to simply motion tracking straight through AE and tying the fire assets to it through a null, but the motion is jittery and not in place. - Here are my attempts justto get the idea:

https://we.tl/t-BKMLyTF1nS

https://we.tl/t-6OgGIbskoD

What would be the most correct approach to achieve this? Should I use one of the mentioned methods, only in another way that is correct or could I try do to it with Trapcode Particular somehow?

2 – Leaving the fire trail after the back tire - Speaking of Trapcode Particular, I though I’d be able to achieve this with it, but again, it seems I just can’t do the right settings. I created a Light and a solid for the particular, then used the pen tool to create the trajectory of the fire trail and used the same position path for both layers and set the Light as Emitter which I selected from the Particular options as the motion source. I selected a fire asset as custom particle and I tried to play around with the settings in Particular, but when I play the preview, the trail doesn’t stay in one place (I think it should be tied to a tracking of the ground so it would move along with the camera), and it still sprays particles, rather than only growing forward and creating a fire line trail. The other problem I see is that I can’t make it follow the perspective of the ground at a further distance, so not only can’t I make it smaller when it’s farther, but I also can’t bend it more from a certain point on. Here's what i tried with Particular:

https://we.tl/t-qRvwUZyNTz

Here's also a clean version of the sequence without any effects:

https://we.tl/t-xwRbViALft

Any guidelines of how to complete points 1 and 2 would be greatly appreciated, all the more that this is my personal music video, and I really hope I'd be able to implement my ideas.

How to

This topic has been closed for replies.

ShiveringCactus

Community Expert

For the fire trail element, you'll need to be able to track the bike in 3D or at least move the light emitter to be in 3D. With your shot being locked off, it might be simplest to manually set keyframes for the emitter light to move back in Z-space. Set one at the start of the movement and one at the end and adjust as needed, but seeing as the bike doesn't swerve from side-to-side, I think you could get away with it.

R

Rick Gerard

Community Expert

The shot has enough details to use Mocha AE to track Transform (position), Scale, and Rotation. You will need to apply some serious color correction to the shot to give yourself enough detail to track, then pre-compose before running Mocha AE. When tracking is complete, Create a large Surface like this:

Then you can apply what I call the Stabilized Power Pin workflow to a duplicate of the original footage, pre-compose, then create your replacement tire effect on a motion-stabilized version of the shot. Throw in a little Camera Lens Blur to match the depth of field and work with some other effects to make the fire believable, then return to the Main comp and apply Corner Pin to your tire replacement layer, and you should have it.

Here is the workflow I would use to complete your shot:

I uploaded a Project file that uses your Set Tire on Fire 2.mp4 footage and replaced the tire. It should geet you started.

My Quick Tips Playlist

tire_replacement.zip

tire_replacement_copy_22-x.zip

Mylenium

Legend

This is a "money shot" VFX composite with no simple answers and as so often, preparation is just as important as post work. None of your shots track because there aren't any stable markers and your bike is simply zooming into the distance, so there's almost no parallax for a camera track. This is a classical case for geometry-based tracking or reconstructing the scene fully in 3D, none of which AE does out of the box. If there were some colored dots, perhaps one could track the scaling and tilting, but otherwise there's nothing to gain here. You would need additional markers in the scene (reference cubes, balls on sticks or even just tape/ chalk markers on the ground) and then derive measurements. Otherwise one would most likely try to matchmove the wheel manually with a 3D modeled version and have it serve as a matte generator, emitter and collision object for whatever particle sim, but honestly, even then none of this is going to be "simple". The Ghost Rider stuff took armies of VFX artist and they used advanced tools like Houdini, Nuke etc. and lots of experience and, no offense, that's the problem. You chew off way too much for your level of experience. Just learning the ins and outs of Particular takes time and constructing a particle system that creates credible fire and interacts with the scene and bike is a whole different thing. I already mentioned the tracking part and of course you need a ton of other compositing to emulate the fire casting light, heat waves, possible color changes in the road for melting asphalt and whatnot. This isn't an afternoon project where you can combine some poor camera tracking tutorial on YouTube with others. This is a shot that even I would probably need quite some time to finish and I've been doing this for 30 years. In your case your best option probably is to just ditch the idea. You would have to reshoot the footage with the camera much farther out to be able to track and later crop the shot to zoom in, you need markers, and you need a lot of work to pull off even a lo-fi, "cheap" version of the effect. It's very likely just not worth it and only will make your video look iffy and embarass yourself.

Mylenium

N

Nick90_Author

Participating Frequently

Hey, thank you for joining the thread.

You're right, this does seem like something above my current skill level, and we don't have any preparation during shooting, because unfortunately this idea came to me after we've shot the video in November last year. So when seeing how the operator shot this scene with severe lens blurring as the bike progresses, really did trouble me even further. But I told myself, that I would try to work on the idea, because I like to challenge myself. Still, I told myself that if the end result doesn't look ok, I would ditch the whole thing, because as you say, I don't want to embarass myself with the end product.

R

Rick Gerard

Community Expert

Take a look at the comp I uploaded and check the tutorials. The shot is plenty doable, you just need some stock footage and some masking, and a comp similar to the project I uploaded.

The biggest trick to making it believable is going to be the color correction and adding glow and blur layers to make it look like the fire is casting light on the Motorcycle. It would probably take me a day or two to make the shot completely believable with Smoke, fire, and illumination layers. All of those effects would be added in a Corner Pined/Power Pined pre-comp.

The easiest part of the whole project would be creating the Tracking data in Mocha AE.

I'm working on a tutorial series for Mocha AE that will be released soon. I had not thought about a similar shot, but it would be a good addition to the series.

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