Pirate 4x4 banner

101 - 120 of 401 Posts

·
Registered
Joined
·
8,741 Posts
Discussion Starter #101
damn, now i'm just gonna have to reinstall autocad and start playing with link setups and arcs and shit now that i'm starting to understand this stuff.

Dallas
 

·
Registered
Joined
·
8,741 Posts
Discussion Starter #102
TNToy said:
Foley - with your "magic" numbers of 36" and 75% of that for the upper link, the pinon will rotate DOWN as the suspension drops, right?

What you wrote was a GREAT primier on link building, but as Air Ride mentioned... with long-travel suspenions (unlike roundy-round cars that only move 2 or 3 inches vertically) it's probably a good idea to keep the links pretty close to the same length, so you don't bind the rear driveline at the diff, isn't it?
Just reading back through a bit and saw this. Does anyone have an opinion on what the magic #s might be for a rockcrawler. It sounds like having shorter uppers will help the way it functions, but will rotate the pinion. 80%? 85% anyone played around with em and have an answer? What about running a CV and rotating the pinion up, at least then when it rotates down it wont be rotating too far down. Am I nuts?

Dallas
 

·
Registered
Joined
·
2,135 Posts
Here's some pics of my unfinished project's rear links.
"J" arms with Johnny Joints.
An earlier version also built by Jim Peterson for his daughter, Amy Bulloch's "She-J", worked very well and won the Legends Class at the SuperCrawl.

Rear Links
 

·
Registered
Joined
·
1,749 Posts
I'm sure this has been answered before but I thought I'd ask it again in this thread so it gets included in the awesome info that has come out thus far.

What is the advantage/disadvantage to using "J" arms instead of straight links?
 

·
Registered
Joined
·
1,507 Posts
Box Rocket said:
I'm sure this has been answered before but I thought I'd ask it again in this thread so it gets included in the awesome info that has come out thus far.

What is the advantage/disadvantage to using "J" arms instead of straight links?
The J arm allows the links to be longer. The actual "J" has nothing to do with it. Its just that the points that the arms are connected are further apart because the lower link is now connected on the back side of the axle tube.

Now the reason why longer links are better is that they provide a more constant anti squat percentage as the suspension cycles or unloads on steep climbs.

In simpler terms, if you have longer links and the rear suspensin lifts up an inch or two (for whatever reason) it will change the overall geometry less than if you ran short links.

Sam
 

·
Registered
Joined
·
9,385 Posts
The advantage is usually ground clearance if you mount them to the top or front of the axle like normal.
In Jaffer's case, my guess is that the advantage would be to get a longer link in a smaller space (short wheelbase).

The disadvantage is strength, which can be made up for depending on how you build them and/or what you build them out of. Considering that, a secondary disadvantage might be that they are a little harder to build.
 

·
Registered
Joined
·
9,385 Posts
No reason you can't go over the top. Looks like Jaffer had a coil spring perch right there though.
 

·
Registered
Joined
·
5,688 Posts
Just re-read this thread again, great tech. Don't let it die just yet..

Question:
What would the characteristics be with infintely long arms that are both parallel to the ground?
Meaning that as the rear axle articulates through it's cycle, the wheel moves straight up and down in relation to the front axle.

-tom
 

Attachments

·
Registered
Joined
·
1,507 Posts
LandCroozer said:
Just re-read this thread again, great tech. Don't let it die just yet..

Question:
What would the characteristics be with infintely long arms that are both parallel to the ground?
Meaning that as the rear axle articulates through it's cycle, the wheel moves straight up and down in relation to the front axle.

-tom
The rig would squat when it accelerates but the squatting effect is very small. I think you would be lucky to actually see it squatting as it accelerates.

What you need to remember is that 4wd really dont accelerate much. Most rock crawling launches are normally at 40:1 so you are only going to get to 15mph or so. Its not like drag racing at all.

So IMO you wont see any squatting but what you will find is that the rear tyres wont bite into the rocks and really agressively launch the rig. The acceleration wont be as harsh as something that runs more anti squat. What it will let you do is drive the rig really aggressively (lots of wheelspin and throttle) and not get out of control (wont hop and bounce etc).

Wont necessarily be less capable most situations but what you may find on some obstacles is that a rig with more anti squat will do better because when they do find traction they will punch the rig forward harder.

Sam
 

·
Registered
Joined
·
5,688 Posts
Strange Rover said:


The rig would squat when it accelerates but the squatting effect is very small. I think you would be lucky to actually see it squatting as it accelerates.

What you need to remember is that 4wd really dont accelerate much. Most rock crawling launches are normally at 40:1 so you are only going to get to 15mph or so. Its not like drag racing at all.

So IMO you wont see any squatting but what you will find is that the rear tyres wont bite into the rocks and really agressively launch the rig. The acceleration wont be as harsh as something that runs more anti squat. What it will let you do is drive the rig really aggressively (lots of wheelspin and throttle) and not get out of control (wont hop and bounce etc).

Wont necessarily be less capable most situations but what you may find on some obstacles is that a rig with more anti squat will do better because when they do find traction they will punch the rig forward harder.

Sam
Thanks for the reply!

Still speaking hypothetically here, again what if the wheels moved in a perfectly linear fashion but instead of straight up and down, they moved at a slant relative to the chassis?

If I understand correctly:
in the top pic, as the rear wheels push forward, they will climb up and move closer to the chassis. Squat.
in the bottom pic, the rear wheels push forward, they will push away from the chassis. Anti-squat.

Correct?

-tom
 

Attachments

·
Registered
Joined
·
1,507 Posts
I see where you are going:

In your top pic - yes as the wheels try to drive forward they will want to move closer to the chassis so it will really want to squat the suspension and in the bottom pic as the wheels try to move forward they want to move away from the chassis so they produce some anti squat effect. The first pic would almost impossible to build unless the links were behind the axle.

Now the other MAJOR thing to remember here is centre of gravity effect. The COG (which is up heigh in to body) will also try to squat the rear suspension as the rig accelerates.

Now the clever thing about all this is that force that the rear wheels drive forward with (assuming that when climbing the front wheels do nothing) is the same as the COG force.

So you essencially have two forces, the drive force that trys to lift the rear of the chassis and the COG force that trys to squat the rear of the chassis. Now the things that effect the interaction of these two forces is the height of the COG (the heigher the COG the more the COG force will squat the rear of the chassis) and the angle that the links drive at (the more highly the links are angled the more they will lift the rear of the chassis)

Now when the COG force perfectly balances the drive force we have 100% anti squat.

Sam
 

·
Registered
Joined
·
5,688 Posts
This is fun. Thanks again.

Strange Rover said:
Now when the COG force perfectly balances the drive force we have 100% anti squat.
:eek:
This makes things WAAAAAY clear ! (If I understand it right..)
100% anti-squat means that on level ground, accelerating neither raises nor lowers the rear end?
0% anti-squat means there is no raising force from the rear suspension at all, so the back will squat down when accelerating?
200% anti-squat means the back end will rise up just as much as it would have squatted if it were 0%? (an equal, but opposite movement)

Please let me be right,
-t
 

·
Registered
Joined
·
1,507 Posts
LandCroozer said:
This is fun. Thanks again.



:eek:
This makes things WAAAAAY clear ! (If I understand it right..)
100% anti-squat means that on level ground, accelerating neither raises nor lowers the rear end?
0% anti-squat means there is no raising force from the rear suspension at all, so the back will squat down when accelerating?
200% anti-squat means the back end will rise up just as much as it would have squatted if it were 0%? (an equal, but opposite movement)

Please let me be right,
-t
Yes - thats how I understand it.

Now you should be able to understand that if you have 200% AS and you apply the power quickly and instantly the rear links will actually throw the rear of the chassis up into the air which will pull the rear wheels off the ground and make them spin. You then loose the lift from the links so that the chassis begins to fall untill again the tyres bite into the ground and take up load and throw the chassis back up again. This is why rigs with a lot of anti squat hop on steep climbs.

Sam
 

·
Registered
Joined
·
5,688 Posts
Strange Rover said:


Yes - thats how I understand it.

Now you should be able to understand that if you have 200% AS and you apply the power quickly and instantly the rear links will actually throw the rear of the chassis up into the air which will pull the rear wheels off the ground and make them spin. You then loose the lift from the links so that the chassis begins to fall untill again the tyres bite into the ground and take up load and throw the chassis back up again. This is why rigs with a lot of anti squat hop on steep climbs.

Sam
:idea:

I'm getting it, I'm actually getting it!

Best suspension thread yet.



(oh and it's spelled "tire"..) :flipoff2:

j/k thanks!

-t
 

·
Registered
Joined
·
12,996 Posts
Strange Rover said:
This is why rigs with a lot of anti squat hop on steep climbs.

Sam
But... they don't. :confused:

Here's a good example that I've thrown out before and not gotten a response to:


First, this is Ken Shupes rig. It climbs loose hillclimbs like nobodys business. While the links are not all on the same plane at the chassis, they're certainly not in line with what you normally see posted on this BB. It clearly has a lot of anti-squat. Typically this one is explained with "well, the tight limit strap allows the rear suspension to just stay jacked up" type of scenario. The problem is that, as you've mentioned, that doesn't seem like it should work. At some point it would lose traction, the tires would spin, and the rear end would drop back down... probably starting the vicious hopping cycle you mention. Heres the pic:


Now, lets make it harder: Suspensions with all 4 links terminating at the same cross member. DSI, Toyman, SnortClown, among others are all running suspenions similar to this: (Toymans buggy)


As mentioned before, he does appear to have a limit strap (cable?)... but IIRC DSI does not run a limiting strap. Now, any and all naysaying on the performance of this style of 4 link has been internet armchair-quarterbacking. These guys are all satisfied with the suspensions performance... and I don't think DSi would be competeing with a suspension that had him pogo-sticking any time he encountered loose terrain while climbing a hill. :confused:

So, can anyone explain why this should or should not work, beyond the usual "Anti-Squat is EVIL" type of thing? :confused:

No?
 

·
Registered
Joined
·
4,166 Posts
TNToy said:
But... they don't. :confused:

Here's a good example that I've thrown out before and not gotten a response to:


First, this is Ken Shupes rig. It climbs loose hillclimbs like nobodys business. While the links are not all on the same plane at the chassis, they're certainly not in line with what you normally see posted on this BB. It clearly has a lot of anti-squat. Typically this one is explained with "well, the tight limit strap allows the rear suspension to just stay jacked up" type of scenario. The problem is that, as you've mentioned, that doesn't seem like it should work. At some point it would lose traction, the tires would spin, and the rear end would drop back down... probably starting the vicious hopping cycle you mention. Heres the pic:


Now, lets make it harder: Suspensions with all 4 links terminating at the same cross member. DSI, Toyman, SnortClown, among others are all running suspenions similar to this: (Toymans buggy)


As mentioned before, he does appear to have a limit strap (cable?)... but IIRC DSI does not run a limiting strap. Now, any and all naysaying on the performance of this style of 4 link has been internet armchair-quarterbacking. These guys are all satisfied with the suspensions performance... and I don't think DSi would be competeing with a suspension that had him pogo-sticking any time he encountered loose terrain while climbing a hill. :confused:

So, can anyone explain why this should or should not work, beyond the usual "Anti-Squat is EVIL" type of thing? :confused:

No?
It works because they have shock-absorbers
 
101 - 120 of 401 Posts
Top