Particles start bouncing?

I’m working my way through BlenderGuru’s flamethrower tutorial using 2.66, and I’m finding a weird effect in preview: as I let the particles play through, if I haven’t made any adjustments to their parameters in a couple of cycles of the default 250-frame scene, they begin to bounce weirdly on the surface–all in sync, like a crowd doing the wave.

If I adjust any of the parameters, they settle down to a more normal behavior for a few cycles, then resume the bounce. I’d assumed it was one of the “Stickiness” settings or softbody parameters that was messing up, but after trying a bunch of different settings, I’m getting disheartened. I’m enclosing the scene–does anybody know what’s up with it?


FlamethrowerParticleWeird.blend (929 KB)

yeah its a bit wierd, ive seen it before though, try baking your sim that should stop it. ( no guarentees though!)

Like a crowd doing the wave… :smiley:

Open the Cache panel and reduce the Cache Step down to 1. That will fix everything. Even better, think of it as a reflex to acquire any time you use particles. It will increase the memory used (Who cares with the gigabytes our computers hold nowadays?) but, most importantly, it will prevent Blender from interpolating the trajectories of the particles. It’s really not good at it…

Perfect–that fixed it. Thanks so much! I figured it was something like that, but was looking in the more immediate-effect settings. This is really useful information.