At the time of grinding, wash and soak poha. KEEP the water from Dal for grinding the batter. This water is what will help with the process of fermentation. DISCARD the water from rice. Grind the Dal first by adding water (from soaked udad) just ½ cm above the level of it. Can add some more later if it is too hard to grind into smooth batter.

You'll have to grind the rice, poha and sabudana in two batches. Use the water from soaked udad, just ½ cm above the level of rice. Grind as smooth as possible. Add more water only if needed. Combine the batter with the udad batter. The batter should not be too thick or too thin. It should be thick at pouring consistency.
Beat the batter in one same direction using your hand for 5 min.

Cover it with a lid and keep in a warm place. If the usual temperature of your country is cooler than that of India or if you are in winter, you need to wrap the bowl in a blanket and keep in the sunlight. It takes 10-24 hrs depending on the surrounding temperature. You need not to add any soda or eno to make idli using such well fermented batter. The idli will be very soft and spongy. Just before making idli add 2-3 tsp salt and stir very lightly so as to maintain the air pockets.