OK. I'm at it again. ( waiting for the mud to dry on my plug mold.) Here's a little sketch of a means to move the rudders without using a hydraulic pump. I checked out some off-the-shelf hydraulic cylinders and with a little modification, they can be adapted to operate as a master/slave combination.
I would need to drill out the orifices so the oil flow wouldn't be so restricted, because the pressure is less than a system using a pump.
By pushing the left pedal ( master cylinder ), oil is pushed into the left slave cylinder and moves the rudder linkage left. With the two slave cylinders linked as opposing systems, this will depress the right slave cylinder, pushing that oil back into the right master cylinder. When a right turn is required, the opposite (right ) pedal is pushed and the oil pushes back into the left slave/master system, making the rudders turn right.
With the addition of a pressurized oil reservoir ( via scuba tank ) and check valves, the entire system would be pressurized to just above ambient, so water wouldn't enter the system.
Although the system is pressurized to prevent incursion of water, the pressure between left and right is essentially the same. As you push a pedal, you're applying force against the rudder linkage, but not against the internal system pressure. ( merely a transfer of oil into one and out of the other ) There's going to be some additional resistance from friction in the lines, but with the correct orifice size, that should be minimal.
With the pressurized reservoir, any leakage of oil past the seals will be made up by the reservoir.
Now, a spring loaded centering linkage at the rudder linkage would return the rudders to center if no pedals are pushed, so when a pedal is pushed, that force would need to be overcome, but it wouldn't take a very big spring to bring the rudders back to center because the system pressure ( scuba tank supplied ) is equal on each side. With a slow steady push on a pedal, it would move the rudder slowly, or with a hard STOMP it could move more quickly. Let off on both pedals and the spring would return the rudders to center. This could also be made to operate with a steering wheel and rack-and-pinion set-up at the master cylinder end. With the right gearing, it could be possible to make steering easier than with pedals that would require direct pressure against the rudders PLUS the spring pressure, although it would take more travel ( turns on the wheel ) than just the short stroke of each pedal.
Any body got thoughts on this hair brained idea ? Frank D.