The Robo 3D is a cartesian type printer with an 8" z height I believe. Adding a kraken would give you about a 4" z height which for all practical purposes is unusable. Unless you can figure out some special mounting for your Kraken on the Robo 8 the concept is not practical.
Fetoman, Tessarect and I have been doing designs to make the kraken work for the R3D. You'd have to use the side ports for the liquid, or add heatsinks for air cooling. Contact me on the RoBo3D forums and we can work on a design!
Btw here's a comparison to show that you actually gain some z-height over using the E3D. Kraken | Dual Hexagon | Dual E3D v5 The stock hot end is roughly the middle size between the E3D and Hexagon.
