Actually; R4 is a type of flashcard, which is used for playing 3d games without any trouble. This card allows homebrew and ROMs to boot on the Nintendo 3ds games from the SD card.
Playing and putting DS games on an SD card without any flashcard is not possible. After a lot of tries, we were tired of being fined a particular way to put DS games on SD cards without R4.
Unfortunately, computer science does not find a way yet for transferring DS games on the SD card without a flash card. You may have r4 and acekard2i for less than $20. Their access will not only allow you to put 3d games only, also you can use them for a bunch of classic games.