I am trying to recreate raindrops falling from a cloud and have done so using the particle emitter. Setting the shape to Line and Emission Range to 90 degrees.It looks OK right now but I do not like how the drops are falling randomly diagnol from left to right or right to left etc.. I want the drops to just fall straight down. How can this be done?
Turn your speed of the emitter down to zero so the particles do not go anywhere then add in the gravity behavior. The particles will be pulled down by gravity just like rain in real life. Now that you have the look you want you can play with the speed and other settings to add some varience to your rain (if you want).
If you want the drops to fall faster, increase the amount of gravity. If you want them to fall slower, decrease the amount of gravity.
If you want the rain drops to fall at different rates, well, then Sir Isaac Newton would like to have a word with you.
You can also raise the emitter so that it's quite a bit off screen and the drops have reached terminal velocity before they show up in the frame. Also, make sure there is some randomness to the birth rate of your emitter so that it doesn't look so uniform.