Another 4 Link Thread

[Duuuuuuuude]

Kinda sorta shown here.

http://www.rccrawler.com/forum/axial-ax-10-scorpion/353094-helheddeds-comp-shafty-7.html#post3488827

There is some suspension chatter on pages 5 and 6 of the above linked thread too but Duuuuuuuude has it covered in this thread.

Yep, that way works too. If you really want to narrow it down, hang it from 3 or 4 different places, or balance the skid on something like Ashton did. When the vehicle is at rest, the center of gravity will always be in the same spot, and the rig will always find its balance there.

 

[Szczerba]

Duuuuuuuude, you didn't touch on swaybars, mainly sway bars in the rear of the truck and how they effect traction. I have used several to combat chassis roll on heavier trucks. There is no way my 15lbs CXT rig could crawl or handle the way it does with out it. Also, alot of guys run them on the Terra-X or Ultra-4 type rc trucks these days.

 

[Duuuuuuuude]

Sway bars are literally another spring in the system, added to keep the chassis and axle parallel to each other. They can be used to compensate for a relatively low RC in relation to the CG, or to keep a vehicle 'flat' when cornering without having to go to stiffer springs. They will also keep TT down because they are not allowing the chassis to roll.

Most of the time you can tune out body roll by making RC and spring rate adjustments, but depending on the design and mass of the vehicle, you may not have the ability to do so. When you run out of options there, add a sway bar.

The down side is that sway bars can inhibit articulation, after all, their sole purpose is to keep the body from rolling away from parallel to the axle.


When setting up my race trucks, I do it without sway bars. I get my spring rates right, get my instant centers in a happy place, and if I think it needs a little more, I will add a sway bar. I have not yet applied my race tuning method to a crawler yet, but I will be soon. I'm very interested in what the results might be...

 

[Szczerba]

So with that explaination it would be safe to say that sway bars also help control unsprung weight on uneven ground? Which I think I kinda answered my own question. And yes, I think sway bars are truck weight specific. Ie, not every rig needs them. And I am referring to go-fast crawlers.

I am probably side tracking this thread.

 

[Duuuuuuuude]

So with that explaination it would be safe to say that sway bars also help control unsprung weight on uneven ground? Which I think I kinda answered my own question. And yes, I think sway bars are truck weight specific. Ie, not every rig needs them. And I am referring to go-fast crawlers.

I am probably side tracking this thread.

To answer your question: they can to a point. Remember that the sway bar is a spring. The stiffer the spring, the harsher the ride. At some point, a sway bar on uneven ground will hurt things because the suspension can't work and the chassis will end up being thrown around.

With the increased popularity of 'go-fast' crawlers, I think its a perfectly valid discussion.

Crawlers are designed with a specific purpose, and race vehicles are designed with a specific, but different purpose. The give-and-take rules still apply to both, and both will compromise one area of performance to achieve a gain in another area.

Crawlers that go fast or race vehicles that crawl are doing double duty, so the compromises change towards the goal of having a well rounded rig. A pure crawler will race horribly, a pure racer will crawl horribly. To make them improve in an environment that they were not designed to handle, you will end up removing performance in the environment that they were designed to handle.

 

[hotwheels000]

So what if leaf srings are thrown in the mix ? Obviously they wont be adjustable like a 4 link, can anything be done other than shock tuning ? What about adjusting your CG with placement of the other components and it effects on the leafer...

 

[Duuuuuuuude]

So what if leaf srings are thrown in the mix ? Obviously they wont be adjustable like a 4 link, can anything be done other than shock tuning ? What about adjusting your CG with placement of the other components and it effects on the leafer...

I'm not sure. Leafs are something I need to study more before I write anything down. Most 1:1 leaf spring systems are left pretty close to factory (not counting shackles, etc), so that tells me that it either doesn't matter, people don't care, or they aren't worth fooling with. That doesn't mean that there isn't room for improvement though.

Hopefully tonight I can get started on post #5, which will be a sort of 'how do I apply all of this'. I may also get into panhards as well.

 

[SDheavymetal]

Thanks for all the info.... now my head hurts.

 

[C*H*U*D]

I like the Carpenter/Drill analogy "thumbsup"

 

[WHITE-TRASH]

I'm not sure. Leafs are something I need to study more before I write anything down. Most 1:1 leaf spring systems are left pretty close to factory (not counting shackles, etc), so that tells me that it either doesn't matter, people don't care, or they aren't worth fooling with. That doesn't mean that there isn't room for improvement though.

Hopefully tonight I can get started on post #5, which will be a sort of 'how do I apply all of this'. I may also get into panhards as well.

Not exactly. Yes most people that run leaf springs just slap them on there and go with it. BUT there is lots of tuning to be done with leafs. Mounting the forward eye higher than the shackle end will make the axle move up and back when compressed. That makes for a nice ride but when climbing over a ledge the axle will attempt to drive out from under the vehicle. It also has massive amounts of antisquat.

Mounting the forward end lower than the shackle end will induce a bit of squat but the axle will not try to drive out from under the rig either.


I played around with most every way to mount leafs and I have always built my own packs from scratch.

 

[Duuuuuuuude]

Not exactly. Yes most people that run leaf springs just slap them on there and go with it. BUT there is lots of tuning to be done with leafs.

And that is why I haven't said anything about leafs. I don't know squat (no pun intended) about them.


Since this is a 4 link thread, I probably won't get too deep into them anyway...just cover the basic geometry.

 

[supermoturd]

This is a great thread! I feel like I've been wasting my time reading Millken! I do have one question, though. In your 2nd post, you start using the acronym "IS" e.g.,

"Your IS is also the point where the suspension links apply force to the chassis. But there is a little bit more to it, in the form of Line of Force (LF). I will get to that shortly."

and

"To find the LF, draw a line through the bottom of the rear axle line and through the IS."

Did you mean IC?

 

[Duuuuuuuude]

:lol:

Yes I did, thanks for the heads up.

 

[supermoturd]

So how do Anti-Squat and Line of Force play out if the planes containing the upper and lower links intersect aft of the rear axle, thereby establishing an IC that is located behind the vehicle? For that matter, what happens when the upper and lower link sets run parallel to each other (i.e., intersect at infinity?)

 

[Duuuuuuuude]

So how do Anti-Squat and Line of Force play out if the planes containing the upper and lower links intersect aft of the rear axle, thereby establishing an IC that is located behind the vehicle?


For that matter, what happens when the upper and lower link sets run parallel to each other (i.e., intersect at infinity?)

Concerning which axle?


I'm not entirely sure, and i dont know that I've ever driven a rig set up like that that handed particulary well.

 

[supermoturd]

Concerning which axle?


I'm not entirely sure, and i dont know that I've ever driven a rig set up like that that handed particulary well.

I had the rear suspension/axle in mind.

Saying that setting up a suspension in the way that I suggested is impractical and unheard of is a good enough answer for me. I was asking out of curiosity.

 

[EeePee]

2. TT is NOT caused by pinion gears climbing ring gears.


TT is simply resistance to a rotational force. You are applying torque to something that is trying not to rotate.

Exactly the same thing. You forgot one word (okay, two), though.

2. TT is NOT caused by pinion gears TRYING TO climb ring gears.

Thus the resistance.

 

[EeePee]

And I'm not comfortable about the sway bar stuff.

Yes, it's the last bit of tuning to be done.

But, the way it works is thusly: :ror:

While cornering there's a weight shift to the outside from the chassis and body which compresses the outside suspension, the sway bar resists the twisting motion, and therefore lifts the inside tire, the chassis reacts with a weight shift to the inside and etc...

It's the sway bar resisting the torsional twisting movement and doing work to the other tire that makes things happen.

 

[Pixelfantasies]

I had the rear suspension/axle in mind.

Saying that setting up a suspension in the way that I suggested is impractical and unheard of is a good enough answer for me. I was asking out of curiosity.

This type of suspension must use a panhard bar or Jbar to keep the axle oriented under the chassis correctly. Pan hard/Jbar set up are typically used in left turn oval track racing. These types of setups are found on asphalt or dirt cars typically set up to turn left. They also use lift arm setups to achieve more anti-squat, and often use a bar or shock and spring setup to control fore and aft roll of the differential as they often use a carrier or birdcage that isn't fixed to the differential for the suspension links.

This is the type of suspension you mentioned in use. Not something that would work well for crawlers persay.
http://m.youtube.com/watch?v=gC3W9Zd_1Pg&desktop_uri=/watch?v=gC3W9Zd_1Pg

http://m.youtube.com/watch?v=pA9Sut0umpY&desktop_uri=/watch?v=pA9Sut0umpY

 

[hpiguy]

Duuuuuude, huge thanks for taking the time to do all of this. I'll need to re-read it many times I'm sure. I'm just starting to learn about actually trying to tune my suspension to get my rigs to do what I ask of them, and all of this is a big help for sure. "thumbsup"