If you want the sparks to go more vertical you just need to modify the Z-axis power on the current Velocity node for the spark explosion in Cascade.
To reduce the count of the sparks you’ll go towards the top area of the particle system under “Spawn”. There’s 2 areas there. One is “Spawn>Spawn” the other is “Spawn>Burst”. The Spawn>Spawn area controls a constant rate of spawning and is likely NOT what you’ll want to change or tinker with for the spark part of the system. The Spawn>Burst should have a “burst list”. Click the arrow on it to open it and check the numbers. The first number is the TIME when the burst occurs (usually somewhere between 0 and 1) the second number is the actual quantity of particles. Change that to reduce total burst count.
I would advise adding in 2 more elements at the very least (in addition to dramatically reducing the spark burst count).
- Add in a round fuzzy glow shape (like the soft brush in photoshop) that flashes for around 0.05 seconds (Lifetime) or less at the very start of the explosion. It should also grow in size over life from very small to very big over a very short duration. This will be the explosion “flash”
- Add in an explosion shape that lasts just a smidgen longer than the flash and isn’t quite as big - perhaps 1-2 times size of robots. This could be a static image which you scale the size by life - OR it could be an image sequence of an explosion. Or if you’re feeling extra fancy, you could even use a mesh emitter to make the explosion shape out of sphere geometry with animated textures on it.
There’s a lot of ways to get any particle system to work right, tinker around, experiment, and pick apart other particle systems that you like for study purposes. Sadly UE4 doesn’t have as much good VFX sample content as UE3, so it might be worth your time to download an old copy of UE3 and examine some of the work in there (Cascade is almost identical in both). Good luck!