Not me, but here's an exerpt from a book I have:
"Only three or four species of piranhas have been bred in captivity. Almost all of these have occured at public aquariums where single-species shoal of adult specimens were housed in aquariums at least 1000 gallons."
One of those species is the red bellied piranhas, of course. So therefore to attempt breeding, you will need a shoal of at least 6 to 8 adult specimens, in an aquarium from 100 to 250g. BTW it takes about 2 years to grow a red belly to adulthood, even in the best of conditions.
If you really have the time, money, commitment et all, then use lots of plants as these guys build nests in the roots of floating plants. Lots and lots of plants... A section of the tank should be thickly planted for that matter. Breeding colors of the red bellies are grey with a lot of silver sparkles on their back. They almost completely lose the red. They chase themselves a lot, and rub their bellies during courtship. When fry becomes free-swimming, they are large enough to eat live brine shrimp.
Hope this answers your question!