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Old 01-21-2014, 12:31 PM   #41
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Default Re: Does a bend in a link effect the geometry of the suspension?

With the link bends facing downward, can you flip the rig over and replicate the suspension behavior from the first video? Essentially, using the forces applied during "reverse" rotation/axle wrap?
(I know you don't use reverse, I'm curious...)
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Old 01-21-2014, 01:06 PM   #42
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Default Re: Does a bend in a link effect the geometry of the suspension?

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Originally Posted by Duuuuuuuude View Post
Just for giggles, can you do it again with the bends near one end of the link?
This run has the same offset as the 15 degree bend, which is ~1/2". The dimension (Horizontal axis in the graph) is the distance the bend is from the end. 2" is the center, and it goes up from there. You can see that the closer the bend is too the end the more displacement in the link under identical load conditions.

https://lh6.googleusercontent.com/-M...ity_offset.jpg

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Old 01-21-2014, 01:37 PM   #43
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Default Re: Does a bend in a link effect the geometry of the suspension?

Cool. Now give it a crazy bend like what was seen in the videos.
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Old 01-21-2014, 03:05 PM   #44
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After watching the video it dawned on me that with the bend towards the uppers the longer straight part of the link attached to the axle the forces of the axle transfer through the long straight part first which turns the bend into a lever on the shorter straight part of the link connected to the upper. So in short the force doesn't travel in a straight line from rod end to rod end.

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Old 01-21-2014, 03:59 PM   #45
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Default Re: Does a bend in a link effect the geometry of the suspension?

.


By holding the rear axle in your hand as you did it put tension pulling on the upper links. Look at how the tension on the upper links pulls on your chassis. One pulls the chassis down while the other pulls it into the shock mount. The one pulling down will squat more as seen in the videos.






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Old 01-21-2014, 07:00 PM   #46
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Default Re: Does a bend in a link effect the geometry of the suspension?

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Originally Posted by o-o View Post
.


By holding the rear axle in your hand as you did it put tension pulling on the upper links. Look at how the tension on the upper links pulls on your chassis. One pulls the chassis down while the other pulls it into the shock mount. The one pulling down will squat more as seen in the videos.











Completely wrong.










Not exactly a nice cad drawing, but the idea is there. If the black dots were exactly the same distance apart as in link ends, both links would behave the same if there was no flex and no binding.


The suspension does not care if the links are bent, straight, curved, etc. The axles will follow the same path all things being equal. Now the zig zag link would need to be 100x stronger because of all the forces involved, but the axles would follow the same path no matter the shape of the link as long as they are the same length.


Straight bars have the advantage of no bends to weaken the bar. That is why the upper links on most cars can be a lighter design because they are usually straight and shorter than lowers. It is basic design.


I would venture to say the first video there is some sort of binding going on. Not that I would say shaking a car by the rear axle is a scientific way to design and test a suspension 4 link.
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Old 01-21-2014, 07:00 PM   #47
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Default Re: Does a bend in a link effect the geometry of the suspension?

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Originally Posted by SkaldidDog View Post
From the other thread.

Imagine one of those crazy straws, the liquid still goes from your cup to your mouth. Same as a straight straw. Two points lie on a line, independent of how you get there.

J
This maybe more liquid dynamics than geometry, but isn't more force (suction) required when using a crazy straw than a straight one?
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Old 01-21-2014, 07:04 PM   #48
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Default Re: Does a bend in a link effect the geometry of the suspension?

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Originally Posted by The Violator View Post
Completely wrong.










Not exactly a nice cad drawing, but the idea is there. If the black dots were exactly the same distance apart as in link ends, both links would behave the same if there was no flex and no binding.


The suspension does not care if the links are bent, straight, curved, etc. The axles will follow the same path all things being equal. Now the zig zag link would need to be 100x stronger because of all the forces involved, but the axles would follow the same path no matter the shape of the link as long as they are the same length.


Straight bars have the advantage of no bends to weaken the bar. That is why the upper links on most cars can be a lighter design because they are usually straight and shorter than lowers. It is basic design.


I would venture to say the first video there is some sort of binding going on. Not that I would say shaking a car by the rear axle is a scientific way to design and test a suspension 4 link.
Did Jeremy give you all that info?
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Old 01-21-2014, 07:26 PM   #49
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Default Re: Does a bend in a link effect the geometry of the suspension?

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Originally Posted by Curcal View Post
This maybe more liquid dynamics than geometry, but isn't more force (suction) required when using a crazy straw than a straight one?
Thats because it becomes a length and gravity equation in that case. They would need to be the same length, and have the same change in eleveation, since you have to account for the weight of the fluid being acted on by gravity.

But that doesnt help here.
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Old 01-21-2014, 07:51 PM   #50
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Default Re: Does a bend in a link effect the geometry of the suspension?

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Originally Posted by ROWDY RACING View Post
Did Jeremy give you all that info?
Nope, that would be the years of building hot rods. Hot rods that actually get driven. And drive down the road straight, handle well, and launch straight without a ton of wheel hop. And reading the books I listed earlier. The ones pictured are the 2nd set I bought. The first spent years in the shitter of my shop being read over and over. It is amazing the things that can be learned while dropping Novaks. I worked for a guy who raced pro stock drag cars and learned as much as I could from him on set up, and how to make a car hook up. It is amazing in the real world how a 1/2 a turn on a 4 link can make the .01 second difference between going to the next round and packing up and heading 1000 miles home.


Jeremy is a numbers guy, he runs his designs through lots of modeling software to see what things are happening. I personally do not think it makes that much difference on these cars, they tend to be so loose anyway, but it makes sense to start out with a design that you know has a shot of doing things you intended them to do.


When i see designs that stagger the upper link mount holes back and forth it makes me laugh. There is no way to account for all the things that happen when you not only move the upper links back but also up just a hair. Poor design for having any consistency, IMO.
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Old 01-21-2014, 07:53 PM   #51
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Default Re: Does a bend in a link effect the geometry of the suspension?

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Originally Posted by The Violator View Post
Completely wrong.













The suspension does not care if the links are bent, straight, curved, etc. The axles will follow the same path all things being equal. Now the zig zag link would need to be 100x stronger because of all the forces involved, but the axles would follow the same path no matter the shape of the link as long as they are the same length.


Straight bars have the advantage of no bends to weaken the bar. That is why the upper links on most cars can be a lighter design because they are usually straight and shorter than lowers. It is basic design.


.
I'm not arguing at all that the axle will follow the same path as the suspension cycles, I know it will. What we are trying to understand is why the suspension compresses more with the links one way than the other. The force applied in the video was not a downward, suspension compressing force. If the same amount of weight was set on the car, the suspension would compress the same amount with either link or the zigzag link you drew. However, it compressed more with one link than the other in the videos. The force applied wasn't a downward force, but a twisting force as if the car was being driven. The top link has tension applied to it, which pulls on the frame. The angle bent in the link creates a vector that will not pull the same direction when flipped upside down.

The only way a bent link would pull the same force when mounted either way is if both attaching points are on the same horizontal plane, but in this case it looks like the mounting point on the car is higher than the mounting point on the axle.


Looking at the pic below, remember that force the upper link "sees" is a pulling tension force, not any type of downward weight compression force. No weight has been applied, only a twisting motion that will pull the link away from the frame.

In the top illustration the point of pull is on the same plane as the point of resistance, so it wouldn't matter the orientation of the link as each situation is identical. Now in the bottom illustration, the lower black dot is the axle mount point and the higher black dot is the car mount point. Looking at the bottom illustration you can see the green link will pull down on the black dot with more force than the red link. It all has to do with vectors when the direction of the pull is on a different plane than the point of resistance.


[/URL]
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Old 01-21-2014, 07:54 PM   #52
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Default Re: Does a bend in a link effect the geometry of the suspension?

Theoretically, I believe the forces should be the same upon a bent or straight link.

the issue however though, is that links bend, and the forces applied to the links will differ greatly upon the whether or not a link is bent or not. Therefore the bends in the inks will absorb/deflect some of the energy applied to them.

Simplest way I could describe it would be if you had a straight link between point A and pont B and had direct lnear force applied between the two points. Very little energy would be absorbed by link deflection.

However, if the link between point A and point B were shaped like an "S" and the same linear force used in the first example was applied, the link would compress (whether you can visually notice it or not) and absorb some of that energy, and in the end rebound and redirect the force.

Last edited by TSK; 01-21-2014 at 11:38 PM.
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Old 01-21-2014, 08:10 PM   #53
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Default Re: Does a bend in a link effect the geometry of the suspension?

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Originally Posted by Erik D_lux View Post
Just more food for thought...

My bends are pretty impractical in the video, but what about a bent rod end? I would guess it should have the same impact on a smaller scale?

Couple things I would like to add-

1-WOW That sure is a sexy axle in the pic!
2- get that guy some paint, his motors all rusty and crap.
3- who runs rodends like that on the upper link?
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Old 01-21-2014, 08:18 PM   #54
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Default Re: Does a bend in a link effect the geometry of the suspension?

But really, the links obviously changed something in the video. I can't understand why, but it did. I am thinking that because the lower links are mounted above the axle centerline of the axle and by holding the truck by the rear axle, it puts so much pressure on the upper links it causes them to flex. Weather you can see it with the eye or not. When they flexes it might be letting the lower link mount at the axle push the lower link up causing? Could that cause squat?
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Old 01-21-2014, 09:29 PM   #55
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Default Re: Does a bend in a link effect the geometry of the suspension?

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Originally Posted by o-o View Post
I'm not arguing at all that the axle will follow the same path as the suspension cycles, I know it will. What we are trying to understand is why the suspension compresses more with the links one way than the other. The force applied in the video was not a downward, suspension compressing force. If the same amount of weight was set on the car, the suspension would compress the same amount with either link or the zigzag link you drew. However, it compressed more with one link than the other in the videos. The force applied wasn't a downward force, but a twisting force as if the car was being driven. The top link has tension applied to it, which pulls on the frame. The angle bent in the link creates a vector that will not pull the same direction when flipped upside down.

The only way a bent link would pull the same force when mounted either way is if both attaching points are on the same horizontal plane, but in this case it looks like the mounting point on the car is higher than the mounting point on the axle.


Looking at the pic below, remember that force the upper link "sees" is a pulling tension force, not any type of downward weight compression force. No weight has been applied, only a twisting motion that will pull the link away from the frame.

In the top illustration the point of pull is on the same plane as the point of resistance, so it wouldn't matter the orientation of the link as each situation is identical. Now in the bottom illustration, the lower black dot is the axle mount point and the higher black dot is the car mount point. Looking at the bottom illustration you can see the green link will pull down on the black dot with more force than the red link. It all has to do with vectors when the direction of the pull is on a different plane than the point of resistance.


[/URL]




The forces would act exactly the same on both diagrams. The force is going to act as is it is a straight line between the 2 black dots, no matter the path of the link.


Again the 4 link bars do not care about their shape, bends, etc. As long as they do not bind, etc. They are like Rowdy, they act straight even if they are not. The bends only introduce weak spots.
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Old 01-21-2014, 10:18 PM   #56
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Default Re: Does a bend in a link effect the geometry of the suspension?

Apparently it does matter bent or straight. Wrap your minds around that! Unfortunately we aren't dealing with straight line physics, the axle is applying 2 forces on the chassis using a rotational force. However small, it's still there.

Now look at the angle both setups leave the axle, that force will be altered as seen.

So, IF everyone agrees it doesn't matter how they are bent or even straight, the force acts between A-B, then nothing should change. As seen in Erik's videos, crappy yes, something has changed. With the first comment accepted, rule that out and consider another variable which is what he is trying to determine to begin with.

I propose a revision to the first question.....does a bent link affect performance characteristics on a crawler? That should be a resounding "YES"....it's been proven, you figure out why.

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Old 01-22-2014, 01:25 AM   #57
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Default Re: Does a bend in a link effect the geometry of the suspension?

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I propose a revision to the first question.....does a bent link affect performance characteristics on a crawler? That should be a resounding "YES"....it's been proven, you figure out why.
When was it proven?

Another thing I was thinking. And this is purely coming from my own experiance.

I realize noone runs metal rod ends, but how would the same "test" be affected by swapping to them? I'm willing to bet that it tightens right up. And along those lines, its a possibility that the tolerances between the rod ends was differant, being that they where differant links?
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Old 01-22-2014, 01:37 AM   #58
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Default Re: Does a bend in a link effect the geometry of the suspension?

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They are like Rowdy, they act straight even if they are not.
Lmao
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Old 01-24-2014, 02:10 PM   #59
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Default Re: Does a bend in a link effect the geometry of the suspension?

Gotta say Erik, this is the awesome stuff I like to see on this board. Challenging math and physics to try and explain why things are what they are. I'm no engineer but I believe the geometery and motion is only related to the distance from eye to eye in this situation. The bend should produce no factor other than binding. Yes, this angle is extreme and not likely my go to on future builds . But I love this test and something does need to be explained there! Maybe one of you masterminds will come up with a way to test in another controlled way? There's a reason you guys are the best at this, never leave it alone
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Old 03-02-2014, 10:25 AM   #60
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Default Re: Does a bend in a link effect the geometry of the suspension?

I am starting a 2.2 build using the YTC DA chassis and RC4WD Bully 2 axles. The hardest thing for me to figure out being new/b to 2.2 crawlers is the lengths needed to order from VP for each suspension link.

If they were all perfectly straight, roughly what lengths would be a good starting point to order?

Since I will have to bend the lower links myself, which makes me nervous, what is a recommended angle and starting length for the lower fronts and then the lower back links? What should the final point to point length be after a bend?

I tried to find a source for pre-made bent links in the vendor's section, but have not had any luck yet.

Any advice or links to other threads would be most appreciated!
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