RSSR linkage

[red300zx99x]

need help with the math for analysizing the postion of a RSSR linkage, say giving the input angle of one of the R joint and and output of the second R joint. I have a method using rotation matrices, but this function is very computer intensive and takes awhile to calculate. Any help would be greatly appreciated. Never taken a statics or dynamics class, but not totally ignorant of the subject.

 

[desertfox]

Hi red300zx99x

Whats an RSSR linkage? and can you give details of length of links, forces etc and what exactly are you trying to workout is it just a position or velocities, acceleration.

regards desertfox

 

[red300zx99x]

it's a spatial 4-bar linkage, revolt joint as the anchor connected by a link to a spherical joint connected via linkage to another spherical joint ending with a link to another revolt joint. R for revolt joint S for spherical joint, hense RSSR. It's what independant suspension cars use, the RS links arm the a-arms and the SS link is the upright or spindle. In my case i gets alittle more complex. RSSR-SS is the technical language I believe, the second SS link being linked to a point on the spindle, which in turn is connected to another RSSR link, the steering 4 linkage, which happens on both sides. So 3 RSSR's, connected by to SS links, wheh. Position analysis of RSSR is what im looking for, but any info on the rest would be greatly appreciated too.

 

[GregLocock]

I hate your terminology, where does that come from?

Anyway as described RSSR has one undefined degree of freedom, the spin axis of the spindle. You'd have to use RSRR.

If the entire frame lies in one plane with normal R axes then it can be analysed by any of the wishbone analysis programs mentioned in the suspension FAQ.

Adding the toe link complicates things, Racing by Numbers or Wishbone.bas will still handle it, I think. If you do have a single plane for the wishbones then it is easy to work out the steer effect of the toe link, by hand or graphical construction.







Cheers

Greg Locock

 

[desertfox]

Hi red300zx99x

Struggling to find anything to help sorry.

I have found a lot of sites which give analysis to four bar linkage mechanisms but these are planar.

You might have better luck if you post this in Automotive
Suspension engineering.


regards desertfox

 

[red300zx99x]

The RSSR linkage is what im worried about, the spin axis of the spindle is and figuring out the resulting wheel plane is not computer intensive, and part of a seperate function I'm working with. Sorry trying to optimize one function before another here. But anyways, all spatial mechanisms here, im looking for help with the hand calculations descirbing the motion of each link given some input angle of one of the a-arms...wishbones, dammit I wish we could all use the same terminology across the world. It's 5:30 over here in the states....weary eyes, but another question Greg, are there wombats on the highways?

 

[GregLocock]

Oh yes, the only one I've seen in the wild was in my headlights, 1 second before we hit it.

Cheers

Greg Locock

 

[Dennyd]

red300zx99x,

If you have the kinematic equations that describe this linkage and solving them is your problem then I'd suggest TK Solver. Frankly, anyone involved in technical calculations should have this software.

If your issue is coming up with the kinematic equations then I'd suggest you research areas of robotics. These types of linkages, but more importantly dealing with their math, is very common to robotics. It's been 23 years since I did this in college, but I remember we had plenty of resources for it.

By the way, what is your application. Your original post doesn't give even a hint.

- - -Dennyd, P.E.

 

[mloew]

All,

Please see the FAQ Resources for Mechanism Analysis and Synthesis (faq404-804). I hope this helps.


Best regards,

Matthew Ian Loew
"I don't grow up. In me is the small child of my early days" -- M.C. Escher

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[red300zx99x]

Suspensions in autos. Have found a few citations of RSSR analysis and synthesis in robotic literature, having problem tracking down the actual papers though. Even found one on the whole RSSR-SS structure, something about creating linear toe curves and such. One paper that was found was from IBM, used an 'alternative' solution to the situation using tensors. Haven't tried this yet, learning the tensor notations now, but if this is an alternative what is the usual solution.

 

[mloew]

Greg,

Unfortunately, the terminology is fairly common, at least in the US. A conventional SLA suspension is indeed a RSSR-SS type. To steer this, the last "S" would need to be connected to a slider. I forget how that would be abbreviated. I think there are better ways of describing kinematic architectures.



Best regards,

Matthew Ian Loew
"I don't grow up. In me is the small child of my early days" -- M.C. Escher

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[red300zx99x]

No slider here, draglink, idler arm and steering box, another RSSR to add to the headache. But if one RSSR can be computed, there are few worries in connecting the 3....anyone, anyone?

 

[mloew]

red300zx99x,

Greg might have a bit more confidence in his ability to do this type of analysis classically than I do in mine. I would be (and have) done this type of kinematic analysis with the help of Pro/ENGINEER. I have some similar work detailed in the thread All Wheel Steer Mechanisms (thread60-54516) where I had a front suspension with independent suspension (2 spatial four bars) connected to a center steering mechanism (planar 4 bar) via tie-rods (2 additional spatial four bars) plus the steering input mechanism as you have (yet another spatial four bar). For the front axle system alone it was ultimately a spatial 13-bar mechanism (mobility 3). The rear twin axles were even more complicated.

Best regards,

Matthew Ian Loew
"I don't grow up. In me is the small child of my early days" -- M.C. Escher

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

300zx, what is your objection to using the suspension analysis programs that were suggested? Or do you want to see how to do it by hand? If so, I was taught to draw velocity diagrams in drawing class, but we had no textbooks, so without a drawing board it is a bit hard to explain!



Cheers

Greg Locock

 

[red300zx99x]

I'm in the process of writing a vehicle simulation program, much fun I must add. As of this moment I can move the linkages using matrices, but this is very time consuming, so I'm in the search of faster methods.

 

[GregLocock]

Oh fair enough. A matrix is the fastest solution, so far s I know, for a general solution.

Cheers

Greg Locock

 

[red300zx99x]

Actually, the movement isn't the hard part, finding the angle of rotation for each link is what is the time consuming part