Soaking with enough water ensures dal and rice both gets double in quantity
of water and grind in high speed for 30 secs to a min, add 1/4 - 1/2 cup of water again and grind until smooth, urad dal batter will be soft, fluffy and smooth if grind properly with enough water.. If your mixer start making noise add more water.
water, add this water to prepared batter with salt and mix gently to combine everything together, using hand is best option (you can skip soda, generally I add).
If your weather conditions is cold it might required another
extra to ferment
Off flame and allow it to cool, take out the idli stand and sprinkle little water on each plate, use a spoon to scoop out idli