The level of the basic income would have to be set at a level that the majority of the population is still willing to work to get more money than the basic amount, so that required work is still done. (The robots are not going to be taking over all the jobs for some time). From the proposals I have seen, it would be near the poverty level in the developed countries.

At that level, I believe there have been enough experiments to validate that most people would want to work to earn more than the minimum. There is a lot of studies showing that many people want to contribute, rather than sit around.

The problem may be effect on tax system. [This other question on menial tasks seems to be related to your question.][1] If there is no increased taxation to match the increased transfers, inflation would be quite high, given the size of the program. (This is discussed in my answer on the linked question in more detail.)

  [1]: https://economics.stackexchange.com/questions/16851/universal-basic-income-menial-tasks