Small correction - ALL motions in wishbone bases suspension designs are rotational.
All geometries cause some amount of rising or falling of the rate of compression of the spring - sometimes even one then the other.
You have to watch the angles between the links to establish whether the rate is rising or falling. Most of the angles in the line drawing are closing as the wheel bumps therefore causing a falling rate. But, because both ends of the spring are being actuated the net result might be a rising rate. It would take some maths to work it out.
Ive been set an assignment from uni to design a suspension system that has adjustable rising spring rates. Basicly we are not allowed to use a progressive spring, and the system must be cheap/light for use in the Fromula Student events.
If this is the brief then the cheap simple solution is the single rocker, with slots on the arms to move the pickup points. I would say it needs a ballrace for precision and smooth operation, perhaps a single race would be cheaper than two. Rose joints to pushrods and damper shaft. You need a sturdy pivot pin on the chassis too. Perhaps the rocker is constructed from two Carbon Fibre plates,(fulfilling the light part in the brief), held apart by the rose joints with a tubular insert to serve as a bearing carrier. It's already been designed of course but your brief doesn't ask you to come up with something new or revolutionary, and because it uses the key word cheap you can carry it off. You therefore appear to be overthinking it and strictly, your brief is easy to fulfil. It may be even cheaper with Ally plates and a greased bronze bush, the ally being the light part.
IIRC most of the formula student cars are this way already, no.
Now if you really want a challenge, one with a potential positive financial outcome, you should have taken on the LSD for formula student brief. That's the most expensive part of the car isn't it? Many teams would wholeheartedly embrace ie purchase a cheap purpose built one wouldn't they? Don't take me up about that, I think I've mentioned all I know.
Remember, design, like art, when done well, is almost effortless. Advances in basic sciences is what usually permits advances in design. The mobile phone had been conceived, designed and was utilised in the original Star Trek series in the 1960's. It took advances in basic science to make it possible.
