Dear Deepat,
I make Idlis only with Idli rice which is bought in paris and saarbrucken ...
I take 1 measure of Urud Dhal and add little Vendayam ... Mix them in water and keep aside.
Now take 4 cups of rice (mostly Idli rice) with water and keep them aside.
Normally, I immerse them overnight and grind it next day morning ... else sometimes, I Immerse it in Day (in morning) and grind it in evening (at 6:00 pm.) ...
After Grinding them, I put 1 tsp of Baking Soda as we are in Cold country ... Next day, you can made soft idlis ...
But, I grind them in Grinder and I am not sure that how well it comes when you grind them in Mixie .. Hope I have helped you and let me know if you have any doubts ...