Can you replace the hydraulic motor with a hydraulic cylinder?
If so... why not duplicate the internal cylinder with a cylinder on the outside of the tank. Pipe the two together, fill the system with oil and bleed all air out. Apply force to the cylinder outside of the tank and you will get a corresponding motion inside the tank. Apply your control sensors to the cylinder outside the tank and you are good to go.
[This message has been edited by Rick Kelly (edited 06-23-2006).]
