That's One Powerful Roomba (Patreon)

I have to say, working with particles in Blender is a headache. Everything looks great in the preview mode, but once I render it, it all breaks. Got it working in the end, just had to re-render it a lot of times. I found a post from one of the developers under a bug report about this, saying that they don't plan on fixing it as the particle system will be changing soon anyway. That was 2 years ago.