I believe that's just the starting position, you want to change the velocity it sounds like. It current goes randomly up and down and left and right. If you only want up and right, try something more like:
'x-velocity' : getRandomInt(0, max_velocity*100) / 100,
'y-velocity' : getRandomInt(-max_velocity*100, 0) / 100 }
So now x velocity will only ever be positive (right) and y velocity will only ever be negative (up).