The 127 Hours star formed Daddy with pal Tim O'Keefe, and recently won acclaim for the duo's Ep debut MotorCity, which features Robinson on the track Crime.
Inspired by the success, the actor has confirmed there's more music to come.
Franco tells Billboard.com, "We have another project that we're working on. I guess if we complete all the songs it'll be a full-length album, 10 to 12 songs. We're working on that right now."
The actor admits he's still amazed he was able to persuade Robinson to be a part of the initial project after a brief meeting.
Franco adds, "He had said he would work on something with me, but I never brought him anything solid. When we started doing MotorCity I asked him if he would sing on one of the songs, and he said, 'Sure'. We sent the songs to him, and he really responded to Crime.
"He just went into the booth and kinda grooved over it. He went over it a whole bunch of times and gave us a bunch of stuff to pick from. It was great to see a master, somebody who had been doing it for decades and was just one of the best."