- Location
- NC Sandhills
You Earthlings are making me VERY angry.
I dunno if Mad Flex is the answer? How does it like Mad Throttle?
I dunno if Mad Flex is the answer? How does it like Mad Throttle?
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REAR 1/4 Elliptical suspensions for XJ's
- Thread starter Beezil
- Start date
- Location
- Indiana-Missouri
woody....
mad flex is NOT THE PRIORITY!
my goal is to design a BALANCED suspension.....due to the chop-back, I have to take a different approach.....my current leaf springs just aren't a good match for my rig.
mad flex is NOT THE PRIORITY!
my goal is to design a BALANCED suspension.....due to the chop-back, I have to take a different approach.....my current leaf springs just aren't a good match for my rig.
- Location
- Bakersfield, CA
I just picked up a set of older Chev 1/2 ton leaves......56" long with 8 leaves. I'm going to work with the 57" MJ main leaf and a combination of the Chevy leaves, with the full length plastic liners I've been using. I should be able to dial it in without using air bags, but I'm still going to move in that direction when I get a little more time. I found a strong bag that will move from 3" to 12", and can handle the suspension hanging on it, but I measured and that's still not quite enough travel if mounted on top of the spring plate. If mounted forward a ways, they would work, but the bag is just a touch too wide. Still looking.......
Beez, sell those stiff springs and play with a softer set of leaves before you go through the hassle of a link suspension........unless you're really that bored.
Have you tried actually going wheeling to reduce the boredom?
Beez, sell those stiff springs and play with a softer set of leaves before you go through the hassle of a link suspension........unless you're really that bored.
Have you tried actually going wheeling to reduce the boredom?
- Location
- Indiana-Missouri
yeah, wheeled not too long ago......
it was great! ripped a pair of doors off, broke 3 axle shaft assys, broke a tracbar mount, and de-laminated my entire framerail in the steeringbox area.....
now the jeep is on jackstands while I position the fullsize axles under them, and I am relocating imaginary links until I am comfortable they will work in the design.
I do not know how much time i will have, but the 1/4 E wants to be designed and bult before moab....
there' nothing like testing new mods on upper hell.
it was great! ripped a pair of doors off, broke 3 axle shaft assys, broke a tracbar mount, and de-laminated my entire framerail in the steeringbox area.....
now the jeep is on jackstands while I position the fullsize axles under them, and I am relocating imaginary links until I am comfortable they will work in the design.
I do not know how much time i will have, but the 1/4 E wants to be designed and bult before moab....
there' nothing like testing new mods on upper hell.
Gil BullyKatz
NAXJA Forum User
- Location
- 2003UB313 Planet ERIS
Ya know Beez....If ya do get tired of those springs and want to sell them....Lemme Know!
They're BOR's right?
Maybe if ya get really bored you could design a rolling setup using these and completely go out of this world!
http://mars.jpl.nasa.gov/mer/mission/spacecraft_edl_airbags.html
Gil Bullycatz
They're BOR's right?
Maybe if ya get really bored you could design a rolling setup using these and completely go out of this world!
http://mars.jpl.nasa.gov/mer/mission/spacecraft_edl_airbags.html
Gil Bullycatz
- Location
- Bakersfield, CA
Beezil said:
We'll be there to either laugh or cry with you.......probably mostly laugh. :laugh:
Good luck with whatever you decide to do. We'll see what we each show up with.
JnJ
NAXJA Forum User
- Location
- San Antonio TX
Bringing this one back.
First off, any updates on your designs/plans (not just beez, but any of ya)?
Second, I think in every 1/4 ellip setup I've seen flexed up there is a ton of rear steer. How big of a problem is this and can it be overcome?
First off, any updates on your designs/plans (not just beez, but any of ya)?
Second, I think in every 1/4 ellip setup I've seen flexed up there is a ton of rear steer. How big of a problem is this and can it be overcome?
Quarter elip has nothing to due with rear steer.
How the links are located, their length and the travel geometry of them is what dictates rear steer.
It is maybe more pronounced on quarter eliptic set-ups because of the typically greater travel, but the effect is a result of the linking and not the spring.
I have rear steer but it's because my lower links run parallel to the frame (or perpendicular to the axle). If the lower links are angled inward toward the vehicle centerline, rear steer is reduced. You can even do a lower wishbone set-up and completely eliminate rear steer.
You need to do some 3 view scale geometry (top, end and side) to illustrate, and calculate, the axle position throughout the articulated travel range. Rear steer can be avoided through design. Or, like me, you can live with it and 'try' to drive around it - so to speak.
How the links are located, their length and the travel geometry of them is what dictates rear steer.
It is maybe more pronounced on quarter eliptic set-ups because of the typically greater travel, but the effect is a result of the linking and not the spring.
I have rear steer but it's because my lower links run parallel to the frame (or perpendicular to the axle). If the lower links are angled inward toward the vehicle centerline, rear steer is reduced. You can even do a lower wishbone set-up and completely eliminate rear steer.
You need to do some 3 view scale geometry (top, end and side) to illustrate, and calculate, the axle position throughout the articulated travel range. Rear steer can be avoided through design. Or, like me, you can live with it and 'try' to drive around it - so to speak.
- Location
- Indiana-Missouri
c-rok, I'm having trouble visualizing why a lower wishbone would eliminate rear steer?
if the pivot point is in the middle (the wishbone) and your upper links operate on a radius short enough, rear steer will happen during a droop/stuff situation, at least that's how I am plotting it.
It seems to me that the only way to REDUCE rear steer in a 4 -link, even if one of the pairs is a wishbone, is to keep those links operating in a radius large enough, but still allows for the intended roll center and doesn't affect your designed anti squat.....
I'm stil learning, so i only have a half-understanding of this.....i think
if the pivot point is in the middle (the wishbone) and your upper links operate on a radius short enough, rear steer will happen during a droop/stuff situation, at least that's how I am plotting it.
It seems to me that the only way to REDUCE rear steer in a 4 -link, even if one of the pairs is a wishbone, is to keep those links operating in a radius large enough, but still allows for the intended roll center and doesn't affect your designed anti squat.....
I'm stil learning, so i only have a half-understanding of this.....i think
I'm not sure I'll be able to adequately explain it in words.
Using a scale drawing, it becomes fairly easy to understand.
Imagine your upper links are either a typical 4 link set-up or wishbone.
For the lower links: imagine the axle end being located as far outboard as possible with the frame end angling in towards the center of the vehicle.
As one end of you axle articulates down, that side lower link travels in an arc moving that axle end forward right? Easy to understand. This is the action that generates rear steer.
But what is also happening is that same end of the axle is also traveling in an arc in the perpendicular plane and moving closer under the centerline on the vehicle. Imagine looking at an articulated axle from the direct rear view. The tire is moving UNDER the vehicle.
If you were to look now at a plan view of the link motion with the axle moving under the vehicle, you would see the link effectively pushing the axle backwards and thus negating the forward moving motion of the link dropping.
I might try to sketch this up and scan an image that would better illustrate.
A lower wishbone is fairly easy to understand. The axle pivots about the wishbone center. There is no action pulling the axle ends forward and genertaing rear steer.
Using a scale drawing, it becomes fairly easy to understand.
Imagine your upper links are either a typical 4 link set-up or wishbone.
For the lower links: imagine the axle end being located as far outboard as possible with the frame end angling in towards the center of the vehicle.
As one end of you axle articulates down, that side lower link travels in an arc moving that axle end forward right? Easy to understand. This is the action that generates rear steer.
But what is also happening is that same end of the axle is also traveling in an arc in the perpendicular plane and moving closer under the centerline on the vehicle. Imagine looking at an articulated axle from the direct rear view. The tire is moving UNDER the vehicle.
If you were to look now at a plan view of the link motion with the axle moving under the vehicle, you would see the link effectively pushing the axle backwards and thus negating the forward moving motion of the link dropping.
I might try to sketch this up and scan an image that would better illustrate.
A lower wishbone is fairly easy to understand. The axle pivots about the wishbone center. There is no action pulling the axle ends forward and genertaing rear steer.
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4ward
NAXJA Forum User
- Location
- Dayton, OH
B, I believe he is talking about a double triangulated setup
And if he's not, well, it can still be done. You just have to have a little more room to make it all work. Lower wishbones need to come to a point at the frame end though to get them to work without losing massive clearance though.
My double triangulated 1/4 ellip rear will be on and operating by the end of next weekend. The truss that I need to build has me concerned about basic design principles that I'm in the process of researching.
And if he's not, well, it can still be done. You just have to have a little more room to make it all work. Lower wishbones need to come to a point at the frame end though to get them to work without losing massive clearance though.
My double triangulated 1/4 ellip rear will be on and operating by the end of next weekend. The truss that I need to build has me concerned about basic design principles that I'm in the process of researching.
CW
NAXJA Forum User
- Location
- Coeur d'Alene, Idaho
Does anyone have a 1/4 elip with something other than airbags? I like the idea but I'm not so fond of the price of the airbags. I would like to see pics of coils or the jack bolts.
4ward
NAXJA Forum User
- Location
- Dayton, OH
CW, it's actually kind of rare to run airbags with a 1/4 ellip setup. There are those of us out there that need all kinds of different gadgets to break on the trail though.
Mr. Chark, how drunk were you when you made that post. I too am fond of Hooters (in any form ) You ever gonna take that beast of yours wheelin' again? Why don't ya pull your head out of that other place you call home and get out to Moab and play wit da' boyz.
Mr. Chark, how drunk were you when you made that post. I too am fond of Hooters (in any form
) You ever gonna take that beast of yours wheelin' again? Why don't ya pull your head out of that other place you call home and get out to Moab and play wit da' boyz.4ward
NAXJA Forum User
- Location
- Dayton, OH
Alright, here we go.
Assumed CoG is 82" in front of rear axle centerline and 38" up.
All links are 40".
9" of vertical seperation at the axle, 3.5" at the frame
101" wheelbase.
Antisquat calcs out to be 81%.
The lowers converge at the frame, uppers at the axle.
Links are yellow, frame is red, springs are blue, roll axis is purple.
I'm thinking of moving the upper frame mounts up 1" to get more AS and level the RA out completely. I'm definately open for suggestions as I have a decently remedial understanding of how suspensions work. I'm not sure how much axle steer I have, but there won't be much if I get that RA flat.
Once again, thanks to Dave for helping me get this pic up for you to see and critique.
Assumed CoG is 82" in front of rear axle centerline and 38" up.
All links are 40".
9" of vertical seperation at the axle, 3.5" at the frame
101" wheelbase.
Antisquat calcs out to be 81%.
The lowers converge at the frame, uppers at the axle.
Links are yellow, frame is red, springs are blue, roll axis is purple.
I'm thinking of moving the upper frame mounts up 1" to get more AS and level the RA out completely. I'm definately open for suggestions as I have a decently remedial understanding of how suspensions work. I'm not sure how much axle steer I have, but there won't be much if I get that RA flat.
Once again, thanks to Dave for helping me get this pic up for you to see and critique.
MaXJohnson
NAXJA Forum User
- Location
- The Kansas Rockies
Sean, at a glance, your anti-squat looks more like 120% than 81%. I think you reversed the operators when you divided the numbers.
What CG are you using; vehicle total or unsprung only? Everyone on POR has been basing AS calcs on total vehicle CG (sprung and unsprung) which is wrong. This will give you a % that is less than true AS. The heavier your axles and tires are, the more inaccurate this becomes.
If your drawing is based on total CG, then even 120% is low.
What CG are you using; vehicle total or unsprung only? Everyone on POR has been basing AS calcs on total vehicle CG (sprung and unsprung) which is wrong. This will give you a % that is less than true AS. The heavier your axles and tires are, the more inaccurate this becomes.
If your drawing is based on total CG, then even 120% is low.
4ward
NAXJA Forum User
- Location
- Dayton, OH
Max, I've done the calcs 5 different times so I think I get it right. Maybe I'm using the wrong formula, what do you use?
As far as the cog, I'm doing the pure guess of putting it at the back of the engine, top of the bellhousing. I don't have access to scales, nor could I even attempt to get it on the scales to do the calcs right now. I figure I'll get it as close as I can with the guessing and then I can find a set of scales sometime after Moab. There may be a set over at the Badlands that I can use when I go over there for testing next month though. I was going to go with the back of the crank, but I changed my mind and went with the top of the bellhousing. Pure guess is my junk is going to weigh appx. 3-3500 lbs. with 1200 lbs worth of axles and tires underneath.
Explain to me why you wouldn't use both please. The forces being applied aren't being applied to the axles, they are being applied to the body. My front springs aren't captured, so they won't pull the vehicle down. The only thing that will pull it down will be the limit straps once it hits max downtravel. Almost the same will apply with the rear since I'm running 1/4 ellip. I don't see it pulling down like a normal set off leafs. That seems to be the logical explanation to me, but I really don't know.
Who knows, I may tear the whole link setup off and redo after the test day. It wouldn't be the first time
Oh yeah, I reworked the link locations some, but haven't gotten the drawing up on the web yet. Should be up later tonight or tomorrow.
As far as the cog, I'm doing the pure guess of putting it at the back of the engine, top of the bellhousing. I don't have access to scales, nor could I even attempt to get it on the scales to do the calcs right now. I figure I'll get it as close as I can with the guessing and then I can find a set of scales sometime after Moab. There may be a set over at the Badlands that I can use when I go over there for testing next month though. I was going to go with the back of the crank, but I changed my mind and went with the top of the bellhousing. Pure guess is my junk is going to weigh appx. 3-3500 lbs. with 1200 lbs worth of axles and tires underneath.
Explain to me why you wouldn't use both please. The forces being applied aren't being applied to the axles, they are being applied to the body. My front springs aren't captured, so they won't pull the vehicle down. The only thing that will pull it down will be the limit straps once it hits max downtravel. Almost the same will apply with the rear since I'm running 1/4 ellip. I don't see it pulling down like a normal set off leafs. That seems to be the logical explanation to me, but I really don't know.
Who knows, I may tear the whole link setup off and redo after the test day. It wouldn't be the first time
Oh yeah, I reworked the link locations some, but haven't gotten the drawing up on the web yet. Should be up later tonight or tomorrow.
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MaXJohnson
NAXJA Forum User
- Location
- The Kansas Rockies
Sean,
I'm just eyeballing your drawing. For 100% anti-squat, the line extending from your tire contact patch through the IC will intersect with the front wheel centerline at the same height as the CG. Yours is about 20% above hence the 120% guess. I think the easiest thing to do is draw the 100% line first and then design your IC to land above or below the line depending on your design goals.
Eyeballing is also a pretty good method for locating the CG. There are methods and formulas floating around various websites to calculate the CG by weighing your Jeep on a level surface and then again with one end elevated. This is fine if you have some accurate scales and can elevate one end high enough. The problem is this gives you the CG of the entire vehicle. A while back, I posted a formula to calculate sprung CG based on the total CG, but it requires a a reasonable guess of the weight of your tires, wheels, axles, springs, shocks, suspension arms, drive shaft and steering linkage.
Use the eyeball method, but ignore the unsprung weight. Looking at a sideview picture of your Jeep when you first put in the cage, it appears that the sprung CG would be 6" or more above the top of the tires. If you had 35" tires on at the time, that would put your CG at around 41" or better. It's all a guess. Your 37" figure may be dead on.
The real debate on this topic is; what is the optimum Anti-Squat? Why do I want more, why do I want less? How does driving up a 100% grade (45°) affect the calculations? The effects? I've yet to see some good answers to this.
I'm just eyeballing your drawing. For 100% anti-squat, the line extending from your tire contact patch through the IC will intersect with the front wheel centerline at the same height as the CG. Yours is about 20% above hence the 120% guess. I think the easiest thing to do is draw the 100% line first and then design your IC to land above or below the line depending on your design goals.
Eyeballing is also a pretty good method for locating the CG. There are methods and formulas floating around various websites to calculate the CG by weighing your Jeep on a level surface and then again with one end elevated. This is fine if you have some accurate scales and can elevate one end high enough. The problem is this gives you the CG of the entire vehicle. A while back, I posted a formula to calculate sprung CG based on the total CG, but it requires a a reasonable guess of the weight of your tires, wheels, axles, springs, shocks, suspension arms, drive shaft and steering linkage.
Use the eyeball method, but ignore the unsprung weight. Looking at a sideview picture of your Jeep when you first put in the cage, it appears that the sprung CG would be 6" or more above the top of the tires. If you had 35" tires on at the time, that would put your CG at around 41" or better. It's all a guess. Your 37" figure may be dead on.
The real debate on this topic is; what is the optimum Anti-Squat? Why do I want more, why do I want less? How does driving up a 100% grade (45°) affect the calculations? The effects? I've yet to see some good answers to this.
