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Learning how to build Lotus Seven replicas...together!
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PostPosted: March 15, 2020, 6:51 pm 
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That has been pointed out a few times here but I have no experience with wishbone. I've never drilled down to optimum caster.

A level lca is convenient if it indicates a perfectly horizontal line between lbj and lcap centers. It seems a 70-75 inch SA makes for a very stable RC in X and Y at around 3 inches and good camber gain, with a UCA at around 8 deg.

In Herb Adams book, he was building for a full 8 inches of travel and wanted to ensure the SA would not get shorter than 30 inches in that travel. With less travel and limited roll, you can have a much better camber curve by going to an SA less than 100 inches.

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PostPosted: March 17, 2020, 10:03 pm 
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thanks MV8 for getting those numbers in Vsusp.. I ran them through wish bone along with the 1/2 compression in the tires.. looks great,the RC seems rock solid and stable .. I did add in the caster and tried different steering angles along with some dive and lift in the suspension to mimic going in to a corner transitioning through and accelerating out of it.. The camber seems to have a nice curve to it.. I was surprised to be honest as I thought a swing arm length of around 36" would be to short and cause weird jacking effects.. originally my swing arm length had higher priority in the design process but Ill be reordering my priority list after this..thx

I was struggling to get the rear roll center a bit higher than the front while retaining a swing arm length of around 100" but I should have a better time of it now..

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PostPosted: March 25, 2020, 1:02 pm 
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If your "roll center" migrates, you have a progressive (or regressive) roll rate. You could "combine or neutralize" this using progressive or regressive spring rates.


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PostPosted: April 14, 2020, 12:04 pm 
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Bobber wrote:
If your "roll center" migrates, you have a progressive (or regressive) roll rate. You could "combine or neutralize" this using progressive or regressive spring rates.

sorry Im not sure I follow .. doesn't roll center migration affect geometry moment vs spring rates affecting the rate or speed at which it moves?

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PostPosted: April 16, 2020, 12:58 pm 
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JNS2
I think we are saying the same thing but from different directions.


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PostPosted: April 18, 2020, 12:26 am 
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hey bobber .. your right .. I was looking at it from the other side of the coin ..I follow you now.

Ive got most of my front end components entered int to solid works .. Im hoping to maybe do a rough mock up of the suspension in the next week or so ..
the other thing Im contemplating is the use of progressive spring rates that you mentioned. I have seen a "double rocker" ??set up that compressed the shock on one end and with a link and second rocker compressed the other end of the shock,, the f27 has inboard shocks so I was thinking of this as an option. I believe it would allow for this progressive movement and if done right the ability to adjust ride height with out messing with the springs on the coil-over..that way you can keep the shock in its ideal travel..

when I get some pic up any suggestions would be welcome..

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PostPosted: May 22, 2020, 3:14 pm 
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So I finished My first year of collage !!! ya ...

I took the numbers you gave me MV8 and put them in wish bone along with the caster and steering angle to get the suspension points.
one of my classes we used solid works and were required to do a project.. I chose to do some work on my car... originally I had to rush a few of the item and was was not pleased with the results since then I have gone back and revised the inboard suspension idea..

Original I was inspired by the double dip suspension along with the store version, It seemed to make sense to allow the shock to travel a longer distance.
In this version I am playing with the idea of having a adjustable swedge tube and multiple holes for ride height adjustment. that way you dont have to mess with the shocks every time you want to adjust the height. one of the other concepts I tried to incorporate is that the spring and shock have a progressive movement as they are compressed. It would be nice to have the shock be able to move horizontal along the top rocker arm to be able to increase or decrease the shock effectiveness.. one of the issues at the moment is packaging which may change in the future..

here are some screen shots of the work in progress the front suspension.. let me know what you guys think or if ive over looked any thing..thx


Attachments:
File comment: here is the suspension form the front.. at the moment I only have one corner done
FRNT-ASSY-002 P2.JPG
FRNT-ASSY-002 P2.JPG [ 163.95 KiB | Viewed 203 times ]
FRNT-ASSY-002.JPG
FRNT-ASSY-002.JPG [ 275.65 KiB | Viewed 203 times ]
FRNT-ASSY-002 P3.JPG
FRNT-ASSY-002 P3.JPG [ 259.87 KiB | Viewed 203 times ]

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PostPosted: May 22, 2020, 10:18 pm 
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Location: Cornholio OR "Where the magic happens"
Having the shock travel be less than the wheel travel is a step backwards.
How will you brace the upper arm to keep it from taco'ing?
Messing with progressive spring arrangements is fine but it does the opposite for the shocks.
So the shock would need to be separate from the spring for that to work the way you would like.

A friend went to great lengths to build a pushrod type suspension with ideas along a similar thought line as yours.
It didn't work so well.
At the recommendation of a highly regarded suspension guru,
He removed his dream suspension and mounted a traditional shock setup and was rewarded with a better handling car.

This supports my theory that conventional shocks provide best control working with travel as close to wheel travel as possible.

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PostPosted: May 23, 2020, 12:08 am 
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To address the above issues I believe I have the solutions

1. the upper rocker is boxed 1/8 plate with internal tab and slot style ribbing

2.maybe I have missed the definition of progressive .. In the sense I am using it is in a rising rate of motion between the rocker and the shock and spring . I am not intending to use a rising rate spring.

3. the actual movement of the shock is 108% when compered to the a arm movement "motion ratio?" it is over 1:1
the reason was I was trying to package a user friendly rebuild-able /upgrade-able shock.. I am currently looking at a Bilstien ASN shock with 7" travel.
with over a 1:1 ratio the shock is able to be more finely tuned than a short travel shock.

I believe this set up is more along the lines of a inboard rocker setup.. yes true push rod systems can be / are complex with many pit falls I have attempted to keep this as simple as possible yet being inboard with adjustability in mind.

as always this project has continued to evolve so this probably will not be the last rendition..

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PostPosted: May 23, 2020, 7:12 am 
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I suggest that you look at the steering column location relative to your shock placement.
Davew


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PostPosted: May 23, 2020, 1:39 pm 
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I like what you are doing. Obviously I love rocker arm suspension.


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