A arms and a 3rd link

[Punkur67]

Call me stupid but what is the extra link for. If it to help with deflection in cycle or help hold the arms on in the event that they meet a friendly rock?

[Rick S.]

It will do both. Mostly helps with deflection, taking some of the load off the outer a arm bushings, and mounting points on the frame.
I believe it saved the rear arms in this crash. The nerf and upright were destroyed.
Had the link not been there.... definitely the arms and possibly even their mounts to the frame.

[Fineline]

As I know jack shit about how it works or the mathematics of it I will stay away from that part of the discussion
I have read both sites and still am amazed at how much time you guys put into working this stuff out
And also trying to prove some body else wrong
Who cares if the terminoligy is not correct he is trying to explain it the best way he can
I sure as hell dont understand it and am definety not any sort of expert on the subject but

Doug has all ready proved it works buy putting it onto his piranah
Rick has built a working model of it and posted the pics

I beleive through experiance that the 3rd link would be a great benefit in alot of different ways

It would of helped in this situation as it did to Dougs buggy in the previous photo
Maybe even saved me some money in repairs too






The damage you can see in the photos is only some of it
Also bent the side plates inside the CV cartridge becase of the wheel being completly torn off the A arms and the drive shaft was the only thing holding it too the buggy before it stopped causing the inside cartridge to twist and bend
Could of also been worse still by bending the CV housing and rear of the frame also luckily tho that didnt happen
3rd link definetly would of helped support some of the impact and not let the wheel totaly break free from all mount points to cause the other damage
Maybe I am wrong but I think it would of helped

Keep the faith Rick I think your onto a great thing there

[Carlriddle]

  A picture is worth a 1000 words, and a real working model well thats priceless.

Saw those pic's of Dougs (and video too I think) and it lessened the damage or it world have looked more like Fineline's ride.  Sorry Fineline.

[Punkur67]

Nuff said!

[fabr]

But the FACT that his own model shows a link length change proves that his pivot point does not lie on that axis at all .I am not arguing that this does not work and IMO works very well. As I said previously I think I'll incorporate it into the h arms I will use on this buggy. That does not change the fact though that if ricks model showed no link length change then he would be correct in his axis definition.Since it changes length he is wrong. 

[fabr]

 

[Punkur67]

What about jast making stronger arms. Looks like those arms were thin wall tubing. All of my suspension is made from .120 chromemoly. And if the arms were wider they would spread the load on the car more also.... Just my redneck thoughts.

[fabr]

Now for a serious note.This has been a very good DISCUSSION about a theory. It is not about proving anyone right or wrong.That is not the intention of this site. This sites managements goal is to allow and encourage open and honest discussion that will hopefully enlighten all of us to new ways of thinking about all things to do with fabbing. Rick, I don't see much of your design being used but IMO it was an excellent piece of out of the box thinking and should be used more often. Just a question about the forward mount.I'm thinking of doing it as a threaded stud through a PU bushing instead of a heim.What do you think?

[Rick S.]

Masterfabr,
I don't know what you're smokin, but the fact that the link length can change is exactly what proves the sweet spot lies on an axis. You say you understand why it works, and I believe you.  You think you can work it out on your buggy, then prove it.  My terminology is correct.
The sweet spot lies on an axis that runs lengthwise on the buggy.
Your understanding of the rod's axis, as the suspension cycles, is exactly that. "your understanding"  Imagine a straight line drawn through the earth from the north pole to Los Angeles.  Then another from the earth's center to Los Angeles. Now another from the north pole to Sydney, Australia. These lines are all of different lengths. Yet all are rotating about the same axis. The earths axis. You say "It's not about proving anyone right or wrong." That's fine, I won't tell you that your wrong.
 
Yes, you could use a bushing at the front of the rod if you wanted to.
But the arms could still flex as the bushing gets loaded back and fourth.
I think it functions best as a rigid mount. Remember this rod is seeing tension and compression constantly.

Think about this though, if you fixed the forward mount to a torsion bar it would now help with body roll as well as flexing in the rear. the rod would have to be beefed up and possibly trussed of course.
 

 

[Engineer]

I am sceptical of the torsion bar idea, because of the axis that the rod rotates on.  If you connected the two rods with a bar, the bar would see bending, not torsion.

[fabr]

I'll stop trying to get you to understand that your understanding is wrong if you'll stop trying to convince me I'm wrong.LOL! Like that'll happen!   FWIW though you need to step back and clear your head and listen to what you yourself have said about your "axis".  We both know the link works and BTW the torsion bar idea is bad as engineer said. Also Rick,I hope you understand that I've really enjoyed this discussion. Discussions like this are IMO extremely thought provoking and are quite enjoyable when kept civil like this one has been. Thanks everyone.

[Rick S.]

So I need to step back? Wow.
Geometry if my field of expertise. I designed on the board for 17 years. and now cad for almost 13 This isn't just some hobby for me. I've made my living in this field. I've never been fired from a job and never been unemployed. I have designed countless geometry setting and checking fixtures for the big three. Automated welders, transfer equipment, stamping equipment. What I do is design all types of machinery. Mostly ergonomic equipment where I'm at now. I do these from the ground up. I design, detail, and stocklist the equipment.  I write the controls sequence, and finalize a complete set of plans, for every job that goes out.
I'm known for my understanding of descriptive geometry. I'm usually the one they call to consult about a problem. I'm not saying this to brag, but to qualify myself.
I've enjoyed this too. It ended up right where I figured it would. 

[Engineer]

Don't step back.  It's a good discusion.  With the right mount locations you CAN have three A-arms, or 4 or 6.  I just don't see the benefit of adding more in locations different than the two you started with.  Why not just beef up or broaden their mounting.  In your case the frame was not condusive to extending the arms, so you picked a new location that worked. 

Please exspound on the torsion bar concept.  I don't see how you could connect a torsion bar to the rod and have any effect on body roll.  Mabey if you connect it at the rear right next to the carrier.

[fabr]

Actually I see the benefit of the 3rd link just like rick does. You can only beef up the arms so much and the same with the frame.The forward mount provides a very strong link capable of taking quite a shot to the rear wheel more effectively than  beefing the a-arm or frame.