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PostPosted: April 9, 2021, 6:27 pm 
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Lonnie-S wrote:
They say the Mustang engine will run in a "real stupid" mode if the ECU isn't fully functional, but it is in a real low power, retarded timing state. Not good for driving, but it will do a vroom-vroom kinda thing. :mrgreen:

Cheers,


y wife says I run in that mode all of the time! :lol:

Thom

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PostPosted: April 12, 2021, 7:59 pm 
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I've been doing the back and forth between 3D model, real chassis, and suspension analyzer for a few days. Unfortunately, small changes in pivot point locations can have significant consequences. I'm trying to find the best, all-round solution available to me within the physical realities of the built chassis.

However, what took me a couple of days to resolve was some inconsistent results in measuring suspension locations. I had set up a braced plywood sheet located along the centerline of the car. It was build square when created a few months back. However, it has been in place over some wet months, and what does wood do in the presence of moisture? It moves - frickin' duh!

So, I undid everything and placed it again along the centerline, but shimmed it square this time to correct for the environmental changes in the wood over winter. I also drilled some holes, so I could measure from either side to the same surface.
Attachment:
DSC05685.JPG

Attachment:
DSC05686.JPG


I would prefer to use metal rules, but working alone, a tape measure is much more practical. I've also come to terms with the accuracy I can achieve using these simple measuring tools. I think about 1/16" (~1.5 mm) will be it unless I want to do a little side project to make something new, which I don't want to do right now.

I have my strategy for the rear upper brackets. I'm going to use two small sections of 1/8" angle iron to attach the larger brackets to the chassis member. I've illustrated the idea with some scrap angle below. There will be a piece of angle on each side, pre-welded to the big bracket. I'll use a clamp to squeeze the two sides to the chassis member when placing them, then tack the two angle brackets in place, welding fully later.
Attachment:
DSC05683.JPG

Attachment:
DSC05684.JPG


I did a cursory run of the suspension analyzer software using the latest changes last night, and was surprised to see a 1/4" change in toe in. I was too tired to look at that seriously last night, so I quit for the evening. When I woke up, it was obvious why this was so. I hadn't looked at the steering rack pivot point. It was set optimally for the old bracket arrangement which now has changed. Duh again! Never work on real technical things when you're really tired. I'll look at finding a better location for the new setup.

Cheers,


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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: April 14, 2021, 1:13 pm 
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Some famous race car designer (can't remember who) said something close to, "He who makes the best set of compromises creates the best design."

The practical point is: stay focused on the overall, and don't get obsessive about any particular feature or particular design criteria. I'm afraid I violated that principle. However, I was saved (from the grave) by Allan Staniforth. I'll explain, because we need to learn from each other's mistakes.

I was focusing on keeping my front roll center at 1" and minimizing toe in/out on bump and droop. Because we are mostly using donor parts, we don't have total control over suspension geometry. Certain values are fixed, like the location of the tie rod on the front spindles and the location of the upper and lower ball joints. However, one of the best tools we have to work with is the location of the suspension pivot points on the chassis, which we build ourselves.

So, I kept moving those to minimize the values mentioned above, but lost sight of their effect on other parameters like camber change of the front tires with body roll. When I was doing a simulation of a left turn with body roll, it became apparent camber change on the outside wheel/tire was only slightly less than the chassis roll angle, and it was also positive - not good.

Long story short, in re-reading some passages on camber change in Staniforth's book, "Competition Car Suspension: A Practical Handbook", I found the issue. I had let the upper and lower control arms become too near parallel, making the front swing arm length (front view) become too long, which has the effect of making camber angle change close to the change in body/chassis roll angle. So, at 3° of roll to the right, my chamber change was around 2.5° in the positive direction.

Luckily, I do a lot of simulation, so I caught the issue before I welded anything in place. Over time, I've developed a list of things to monitor, but front swing arm length was not one of them even though the software I use does display the value for you. It's now in my list. Interestingly, it is one of the first values set in Milliken's design procedure (p. 627), but they assume a clean sheet of paper design, and all values for the front spindles are set by the designer, which is not our situation, typically.
Attachment:
Suspension Targets.jpg


So, it is truly "back to the drawing board" and finding a better set of compromises. I thing front roll center height will be one of them. Trying too hard to keep it at 1" off the pavement led me to some (unintended) poor compromises elsewhere.

Cheers,


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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: April 15, 2021, 7:31 am 
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It seems all my recent efforts with different suspensions, to keep the RC from moving around with decent camber gain result in an SA around 65 inches and the RC at 2.5-3 inches.

With a fixed track an inch wider than the rear, fixed lca and uca length, fixed level lca, and 0.5-1 deg neg camber, the only thing left is setting the UCAP location/UCA angle for your SA and possibly minor tweaks of the LCAP height. Did you ever enter the dims in vsusp for comparison? What could it hurt? You must already have these dims for use in the other program. Why not share the x-y dims so others using these parts could compare their own measurements or decide if they want to use these spindles?

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PostPosted: April 15, 2021, 7:58 am 
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Lonnie
I think you are on the right track when looking at a higher front RC. With a solid axle you are probably going to have a rear RC around 8" or 9" using the book type design. You are better off having a roll center axis that is not on a steep angle. More equal wt transfer front to rear. I have about 4.5" Front RC with a 8+" Rear RC that has the roll center moving less then a 1/2" up to 3 degrees. Gives you, neutral cornering, unless you use power over steer.
Davew


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PostPosted: April 15, 2021, 11:53 am 
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@MV8
I'll have to admit I wasn't paying attention to the swing arm length as an entity. I'm fine with running a comparison using VSUP (if I knew where to find it) and sharing the information. My situation is somewhat unique in that I'm using the Howe Racing ball joints. They have a number of actual ball joints you can use, varying the length to suit your application. So, a user wouldn't be stuck with my setup. They could alter some parameters themselves.
Attachment:
Howe Racing Ball Joint.jpg


I took a day off yesterday, but I'll get back on it today.

@davew
I got very sneaky with the rear roll center, and some other related factors, Dave. Based on readings, and the advice of a builder who had constructed a locost with a Rover V8, I knew the torque and power of my donor engine was going need to be dealt with. Although it's a V6, it matches up very well with a 305 Chevy V8 and the Rover (sedan) V8. I've had the engine in 3 vehicles now, including the donor, which I drove for a year. It's surprisingly good.

So, my Panhard rod can be adjusted for roll center height (~ 4-1/2" to ~7-1/2") plus inclination (up to the right, or down to the right) for torque effects. I have it set to ~6" and horizontal right now. I'll only move it if needed when I get to the testing/development stage after it's finished.
Attachment:
DSC04994.JPG


With the 1" front roll center, my roll axis was going to be about 3°. Like I said, I was trying a little too hard to stick to that original criteria. I'm going to be more flexible this time.

Another side effect of what I was doing is the the roll center would move side-to-side a noticeable amount. I know there is debate about how much that matters versus changes in height, but I'd be interested in you opinion, and that of MV8 too.

Cheers,


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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: April 15, 2021, 5:43 pm 
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Yep, I’m familiar with Howe modular joints.

Since you asked, IMHO:

RC stability is one of the three, primary reasons you don’t see struts on locosts. As for lateral migration, I think consistent or at least slow to change handling (cg distance and vector to RC consistent or minimal change in leverage) through the designed range of roll. An RC that flops around at a fixed ride height in 4 degrees of roll is probably not going to become more stable when encountering real roads and dynamics. Surely this stable static RC will result in a dynamic improvement over a strut but only if you have an opportunity to drive it but if you enjoy the tinkering just as much as driving, what diff does it make if it works? That's next guys problem! :cheers:

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


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PostPosted: April 15, 2021, 6:38 pm 
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@MV8

Thanks for the comments. The changes I made today (next post) did both slow, and lessen the lateral movement of the roll center, among other improvements.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: April 15, 2021, 6:58 pm 
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I spent the day modifying and simulating the front suspension design. Here are the modifications and results.

1) Moved rack back 1" - more realistic physically than calculated ideal position

2) Moved rack down 1/8" for improved bump steer.

3) Added 0.5 degree, static, negative camber.

4) Made static toe 1/16" inward

5) Moved upper control arm pivot point down 1/2"

Results
=====
A) Roll center height 2.30" - static

B) Swing arm length 105 inches - static

C) Toe change on 3" dive 3/32" out, each wheel

D) Toe change on 3" bump 1/8" out, each wheel

E) With 2" steer, 3 degree roll (significant turn):
a) camber +1 degree outward on outside wheel;
b) roll center moves ~ 2-3/8" lateral toward outside wheel;
c) roll center moves down < 1/10"

That analysis was made using the old style kinematic analysis, which I'm most familiar with. The simulation software also does the newer, force-based roll center analysis as an option. I think tomorrow I'm going to run the same design with that modeling technique and see what happens.

Also, as if I haven't made this wonky enough yet, you can join the front suspension model to the rear suspension model (created previously), and see how the two interact together in simulations. The force-based guys say that's the criticall test. If the front and rear don't interact in a harmonious way, and want to do the same thing at the same time during maneuvers, the design will always be sub-optimal.

That makes intuitive sense, but I don't know exactly what "do the same thing" means yet in terms of various metrics. I just know the rear suspension is highly configurable (it's a near-Mallock design) that I feel good about making the two of them work together in reality when the car is finished.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: May 9, 2021, 10:10 pm 
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It's been a while. I've actually been working on the build almost every day, but it has been primarily on the front suspension design and supporting bracketry. This has been quite an educational experience, with many trials, simulations of the trails, and then tweaking the design to get the best result I could within the physical limitations of my particular chassis, which is based on the Haynes Roadster architecture, but has significant differences too.

All the bottom front brackets are tacked in now. I could tack weld in the upper front ones too, but experience tells me to leave them clamped until I have the rear upper design finished and proved out. It's a "just in case" kind of decision.
Attachment:
DSC05711.JPG


It took a while to develop measuring techniques that worked directly and easily. I did find a suite of techniques that I was happy with, and felt was accurate enough. In the end, I did figure out a way to use my simulated axle (1/2" rod), measuring tools and dial level to get things set well enough to
achieve what I consider a good level of precision given my home shop environment. After doing the measure/place/trail/simulate process what seemed like 30,000 times, I grew confident enough to set the brackets by hand using my measuring tools and clamps. I didn't need to make a jig, and I don't think one would be practical given the slight variations in the chassis member from the Haynes design, and my own 3D model.
Attachment:
DSC05705.JPG


Once I had worked out the final model of the layout, the hard part was getting the "packing material" (shims ) of the right thickness and then tapering down one side with hand files so that it kept the geometry correct, was in a good welding position, and could be clamped securely enough to be welded and not move. Also, because the front frame was the first complex part I made, the passenger side of the frame is slightly off from spec. It's actually square where it needs to be, so the deviation is localized to the one tube. In the end, to make it work correctly, the passenger side lower bracket is a one-off. It was built to make the correction needed in place and keep the "axle" parallel and level.
Attachment:
DSC05706.JPG

Attachment:
DSC05707.JPG

I'm happy with the suspension design, and everything fits, including the nose.
Attachment:
DSC05710.JPG

I think the suspension design is pretty good. No doubt, a professional (or experienced amateur?) could do better, but it's my best effort. Here are some static screen shots from the simulations.
Attachment:
Final-Model-Static.jpg

Attachment:
Final-Model-Steer3-Roll3-Dive3.jpg

Attachment:
Final-Model-Dive3.jpg

Attachment:
Final-Model-Bump3.jpg


On to the rear upper brackets tomorrow.

Cheers,


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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: May 21, 2021, 12:34 am 
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Quickie update. Not a lot of detail because I'm tired, and I had to catch up on a lots of posts here since I last updated.

Found a cheap (~$35), 6", height gauge on Amazon and bought it. Designed for woodworking, it still has magnets in the base for table saws, etc. so useful on my build. It's based on the same inexpensive digital calipers we've all been using for a while.
Attachment:
DSC05712.JPG

Below the bottom of the gauge is set atop the 1/2" "axle". Take the measurement, subtract 0.25 and you're done. Much easier than my previous methods.
Attachment:
DSC05713.JPG

Attachment:
DSC05714.JPG

I'm fabbing up the last two front suspension brackets. I had an idea, I needed to develop, and I've done that. Mounting/welding is in a challenging location, so I've needed to try a couple of things.

My crude coupons simulating the actual parts clued me in to how difficult welding the "inside", 1" space between the 2 side brackets will be. It's tricky, but I believe I have it solved.
Attachment:
DSC05718.JPG

I'm getting pretty good at doing quick and dirty jigs. I don't like to spend more time on building a jig than fabbing and welding a part. Clamps, scrap metal, magnets - there all good to me. :mrgreen: Just get the J-O-B done.
Attachment:
DSC05716.JPG

Attachment:
DSC05717.JPG

6 of 8 are heavily tacked. The tape covers the joints, so salt air won't rust them before final, full weld. I'll dust the bare, exposed metal you see with primer after the last two are placed tomorrow.

I think I'll be so excited to move on from this phase that I'll probably wet myself with excitement once it's over. I'll probably indulge in a pint of Ben & Jerry's to celebrate tomorrow. :yay:

Cheers,


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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: June 5, 2021, 11:30 pm 
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I had a two week distraction, but started back on the build today. Before stopping, I was having issues getting the already fabricated rear upper suspension bracket on the passenger side to align. I fiddled and fiddled, but it just was always a little off in some direction no matter what I did.

Long story short, making a series of measurements, the angled tube it was to be attached to (photo below) was out of vertical as seen in side view), and the sides of the tube that should be perpendicular to the chassis centerline simply weren't. Said another way, the tube was leaning slightly towards the front of the car, and it was slightly twisted at the base. This happened long ago when I built the chassis, and I just didn't catch it until now.
Attachment:
Illustrator Vertical.jpg


So, I pondered building a new special bracket to do "field correction", but decided to run a suspension simulation using the best fit I could get with the bracket I have. There was only a very marginal change in suspension behavior, and no significant changes of any kind that I could find. So, I tacked in place the bracket I already had, primered all 4 front suspension brackets, and I'm moving on.

The upper suspension arm on the passenger side will have a slightly narrower base, and it will have about 0.5 degree additional anti-dive. I think I'm good enough.

I'll start setting up to determine dimensions for the front control arms tomorrow.

Cheers,


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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: June 6, 2021, 7:17 am 
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Lonnie-S wrote:
Here are some static screen shots from the simulations.
Attachment:
Final-Model-Static.jpg

Attachment:
Final-Model-Steer3-Roll3-Dive3.jpg

Attachment:
Final-Model-Dive3.jpg

Attachment:
Final-Model-Bump3.jpg


Cheers,


Trying to enter your specs into Vsusp.

What is the front VSA at ride height and zero roll, ground clearance, track width, tire size, wheel offset or BS (if not spec’d but measured, how) and scrub?

I’m guessing the control arms are around 17 and 11.25 inch with uca camber adjustable? Actual arm lengths?

Vsusp measures the ubj and lbj from the WMS and hub cl. Is either ballstud the oem length or are they both custom?

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


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PostPosted: June 6, 2021, 9:43 am 
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@MV8

I'll have to go back to my notes on a couple of those data items. What does VSA stand for?

Some basics are:

a) 6" ride height
b) front tires = 205/40 R17
c) Wheels = 8" x 17" (edit: Found my original notes. BS measured = 5 7/8" [5.875"])
d) Front track = 59.120"
e) Scrub = 1.12" positive

The virtual swing arms are given as lengths, not locations. This was one of the noticeable changes from the asymmetry. They are 127.4" drivers, 143" passenger. It puts the kinematic RC 0.16" off centerline. The force analysis version says: "Meh", no significant change.

Interestingly, the Suspension Analyser 2.4C program calculates the expected, true control arm length based on your inputs. There is a slight asymmetry due to the issue I mentioned. The uppers will be adjustable, so no sweat.
It's calcs are:
Uppers = 11.78" drivers, 11.81" passenger
Lower = 16.99" drivers, 16.97" passenger

With my jig materials (wood) and measuring tools, I'm not going to sweat the 0.02" difference between the lowers. :roll:

Cheers,


Edit: The upper ball joint should be the standard Chrysler length, but the bottom is custom, 1/2" shorter. I'm not sure how the custom, Howe housing might change things relative to a Chrysler standard. One nice feature is I could leave them in the spindle without the housing, and determine the BJ center distances pretty accurately.

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


Last edited by Lonnie-S on June 6, 2021, 9:30 pm, edited 4 times in total.

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PostPosted: June 6, 2021, 9:52 am 
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The virtual swingarm where the pivot point is where a line through the ubj and ucap cl and a line through the lbj and lcap cl converge.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


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