External steering rams?
 

Hi all,
First, Im new here and dont know where else to post my question beside where I can have the best try for an answer.
Im building dual hydraulic steering rams onto my Mercruiser alpha one and I have the cylinder rods on the outdrive side mounted.
The problem is that I can not find the correct sweetspot on the transom for the cylinders to mount....
When I mark the position for the cylinder side mounting plates on the transom in the drive pivot centerline to be drilled and then trim/tilt up the outdrive... the location for the cylinders on the transom changes makin it that the rams have to be extended to get there on the marks.
I played around on the transom with different positions and angles but still the out-drive makes a different turning radius when trim/tilt than the cylinders as their pivot point is more fw to the transom then the wrist pins on the gimbalring.?!!
With a single ram it wouldnt be a problem as the drive would just slightly turn to compensate the difference in turning radius.

I can not find more information on this, the pictures I have and found show bravo drives in the down or trimmed position. Are they still able to be tilted full up or is that a compromise that has to be made with the dual rams.?

Thanks in advance!!
Frankm

I'm curious how are you attaching the rams to the Alpha drive? Are you fabricating an Alpha wing plate? I believe Imco-Nevada still has a single ram Alpha dimensional drawing on their site which may have some value. They also have single and dual ram Bravo drawing which may be helpful for moving from their single Alpha set up to your dual ram set-up.

I am no expert on steering. But I don't believe there is that sweet spot where the rams will not extend when you are raising the drive/s. I move my steering wheel back and forth a bit when I raise my drives, especially when the engine is off and no power steering pump working. This is so the cylinders will have a little fluid moving. I might also learn something with you today.

BTW, welcome to OSO

I have lost more than a few nights of sleep over this. If the pivot point of the gimbal lined up exactly (fore/aft) with the pivot point of the ram ON THE TRANSOM, you could achieve a sweet spot. However, the gimbals' pivot point is a good 5" away from the transom, and the rams' pivot points are only about 1" away from the transom, so geometry says there will always be a bit of travel there. The movement (on my system) will be taken up by the relief valve, but hitting max pressure on the relief valve (900psi) will be harder on the rams than the valve.

Keep them on the same CL as the drive as you have done for optimum position.

The rams will stay in sycn with each other when raised lowered because the fluid stays on the same side of the circuit,(left turn, right turn) regardless of the rams extended position. This goes for both sides of the rams pistons. You are not changing the amount of fluid to extend/retract, you are just moving it side to side, thus not affecting drive turning.

Hard to explain, but draw a quick diagram of the 2 cyl with the ram pistons, and how the 2 hyd hoses are cross connected between the 2 cyl. Then visually extend 1 ram out. The fluid on the front side of that ram is forced to the back side of the other ram, pushing it out.


Turning changes fluid volume between the 2 circuts, trimming doesn't

OMG, I really am an engineering flunkie!! US1, I wish I had read that about 6 months ago. Thanks for pointing that out.

Hey, it sounded good. :)

??? When trimming up and down the displacements are different. Rod side non-rod side. If your drives are straight and you compress the cylinders by lowering the drive there is not enough area in the rod side part of the cylinder to capture the fluid that is leaving the open part of the cylinder. The rest of the fluid builds pressure against the system.

When running and turning left and right you gain and lose fluid equally on a twin ram system.

Twin rams hyd hoses are cross connected, so there is a balance between both circuits. The rod volume is not a factor.

If both rams were connected in such that both the rod sides and the non rod sides were paired together, how would you turn? You wouldn't. You'd turn the wheel, and your drives would try to go up/down, or bust off. ;)

I would assume any small amount of variance would be handled with in the pump valve body.

You are correct.....when turning. But I thought he was talking about raising and lowering the drives, not turning left and right. When you lower the drive and BOTH cylinders compress at the same time then rod side/non rod side does have play a role. right? I use hydraulics everyday am I missing something?

A quick sketch, hold your applause for my Paint CAD skills :)