ntsqd
heratic car camper
I started to post this in that thread and then I thought it might hijack it, so it gets it's own thread.
In the late 90's Coby Hughey (some of you may remember him) wanted to design a radius arm that attached like how the current SD radius arms (& others like Jim's and Duff's) attach, with an upper and lower round rubber or urethane bushing. Make the top links attach to the lower links part-way back and make one of them rigid (or actually adjustable for Caster) while the other could change length dynamically or be locked at some specific length. His idea, and I doubt that he was the first to think of it, was a hydraulic ram with a valve in the plumbing that ran end to end. Open the valve and fluid flows back and forth basically taking that link out of the system. Now you've got the front 3 link mentioned in the triangulated thread. Close the valve and it acts like the solid link on the other side.
A tidy, simple idea that won't work.
There's always just a little air in the system so there's just a little bit of change in length of the locked cylinder that will be possible. That may be OK in practical use, but is isn't the idea killer. The killer is that a hydraulic cylinder's shaft displaces some volume of fluid, so the total volume of the cylinder as it extends and compresses isn't static. In a perfect world if you did manage to get all of the air out it couldn't move even with the valve open. This is because of the fluid displaced by the shaft and the fixed volume of fluid. Since no seal is perfect I think that it would move a little, but not far enough to be useful or fast enough to be useful.
All sorts of different gambits were considered to address this. If you pressurize the whole thing (say from the PS system) then it will have just a little bit to extension bias due to the small difference in piston areas.
The idea that I liked the most, and disliked the most at the same time was to put an accumulator in that plumbing. That can allow for the difference in fluid volume as the cylinder extends and compresses. Putting a valve between the accumulator and everything else would hydraulically lock the cylinder. When the valve is open the accumulator and valve would/could have a mild damping effect on the length change of the cylinder (particularly if the valve's cv is small), which could b a good thing.
But think of the complexity that this system now has! It's no longer tidy and simple.
The other thought was a thru-rod cylinder. At the time of discussion F1 cars had *just* started using dampers built that way and "hyrdo-steering" really wasn't a thing, yet. Finding a hyd cyl built that way would tough at best (at the time) and likely impossible (then). Making something like that could get expensive. but it would give you the means to address just how you're going to mount such a thing on a radius arm.
At about this point in the discussion it came to light that not everyone with a wristed arm was pinning them for street driving and the WAH came along with no method to pin it at all. Which made the whole thing a great thought exercise, but not of much use.
In the late 90's Coby Hughey (some of you may remember him) wanted to design a radius arm that attached like how the current SD radius arms (& others like Jim's and Duff's) attach, with an upper and lower round rubber or urethane bushing. Make the top links attach to the lower links part-way back and make one of them rigid (or actually adjustable for Caster) while the other could change length dynamically or be locked at some specific length. His idea, and I doubt that he was the first to think of it, was a hydraulic ram with a valve in the plumbing that ran end to end. Open the valve and fluid flows back and forth basically taking that link out of the system. Now you've got the front 3 link mentioned in the triangulated thread. Close the valve and it acts like the solid link on the other side.
A tidy, simple idea that won't work.
There's always just a little air in the system so there's just a little bit of change in length of the locked cylinder that will be possible. That may be OK in practical use, but is isn't the idea killer. The killer is that a hydraulic cylinder's shaft displaces some volume of fluid, so the total volume of the cylinder as it extends and compresses isn't static. In a perfect world if you did manage to get all of the air out it couldn't move even with the valve open. This is because of the fluid displaced by the shaft and the fixed volume of fluid. Since no seal is perfect I think that it would move a little, but not far enough to be useful or fast enough to be useful.
All sorts of different gambits were considered to address this. If you pressurize the whole thing (say from the PS system) then it will have just a little bit to extension bias due to the small difference in piston areas.
The idea that I liked the most, and disliked the most at the same time was to put an accumulator in that plumbing. That can allow for the difference in fluid volume as the cylinder extends and compresses. Putting a valve between the accumulator and everything else would hydraulically lock the cylinder. When the valve is open the accumulator and valve would/could have a mild damping effect on the length change of the cylinder (particularly if the valve's cv is small), which could b a good thing.
But think of the complexity that this system now has! It's no longer tidy and simple.
The other thought was a thru-rod cylinder. At the time of discussion F1 cars had *just* started using dampers built that way and "hyrdo-steering" really wasn't a thing, yet. Finding a hyd cyl built that way would tough at best (at the time) and likely impossible (then). Making something like that could get expensive. but it would give you the means to address just how you're going to mount such a thing on a radius arm.
At about this point in the discussion it came to light that not everyone with a wristed arm was pinning them for street driving and the WAH came along with no method to pin it at all. Which made the whole thing a great thought exercise, but not of much use.
it was headed there.
