Hi. I am trying to figure out how to couple two seperately driven shafts so that the speed of shaft B is always at X RPM greater than the speed of shaft A regardless of what speed A and B are driven at. (X is a constant, but the value depends on some still unfinished math, we will say 500 for now.) A--C--B A is a variable speed (1000 - 7000 RPM) 500 HP motor. B is a variable speed (2400 - 16800 RPM) 200 HP motor. B is always spinning significantly faster (anywhere from 1400-9800 RPM faster) than A in the same direction. C is the coupling device. Regardless of how fast A is spinning, I want C to limit the speed of B's shaft to X RPM greater than the shaft of A. Can this be accomplished with C being some type of a Fluid Coupling device? This is the configuration I was thinking of... (sorry for the poor diagram) A--C--D--B E-----| A is connected to C with a direct shaft. B is connected to a differential gear set (D) with output 1 connected to C and output 2 serving as a secondary power path (E). I want output 1 of D to always rotate at RPM(A)+X. For example: (if X is 500) If A is spinning at 2000 RPM and B is spinning at 4800 RPM: I want output 1 of D to be spinning at 2500 RPM. If A is increased to 3000 RPM and B is increased to 6000 RPM: I want output 1 of D to be spinning at 3500 RPM. C will be effectively acting as a speed limiter for B. Is there some type of Fluid Coupling that would accomplish this? If not, do you have any suggestions regarding what configuration I can use? Thanks for any help you can offer.