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Learning how to build Lotus Seven replicas...together!
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PostPosted: April 12, 2017, 5:04 pm 
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Joined: January 16, 2009, 2:17 pm
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Location: Langdon, AB Canada
Okay, so for personal reasons I have dropped out of that competition, however the Satellite project is going forward but this allows me to work on the Locos at the same time, and after a full weekend plus a few hours I have arranged my garage so all three of my major projects are accessible. I am super excited about this because it means I can get back to the original project of building the Locost when I need a budget based destresser.

Onto a question I have, I am trying to get my rear suspension done on the Locost, and I am doing a 3 link and with the fancy calculator that Rod supplied me years ago, I am trying to work things out. The problem is I do not know what I am shooting for in regards to ideal set ups for roll centre, anti-squat, or Roll Axis angle. As a reminder I am doing a solid rear axle 8.8 diff from a 2012 Mustang.

All help is appreciated


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File comment: Locost 5.0, 1985 RZ500 resto-mod, and the pro-touring 1968 Satellite
20170412_135953.jpg
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Convincing yourself you can do it is one thing, convincing your wife it is a good idea is another. Glad I have a great wife!

2012 Jeep Grand Cherokee daily driver
Autocross car currently missing..... building a 1968 Plymouth Satellite with 7.2L of noise making technology.

Build is a plus 2" width, Ford 5.0. Wish me luck.
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PostPosted: April 12, 2017, 6:10 pm 
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Here is what I have figured out so far, taking input before I start fabricating things.


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Convincing yourself you can do it is one thing, convincing your wife it is a good idea is another. Glad I have a great wife!

2012 Jeep Grand Cherokee daily driver
Autocross car currently missing..... building a 1968 Plymouth Satellite with 7.2L of noise making technology.

Build is a plus 2" width, Ford 5.0. Wish me luck.
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PostPosted: April 13, 2017, 12:14 pm 
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Shoot, I posted a detailed response last night (took me about 20 minutes) and it seemed to post just fine. But, this morning, the whole entry is gone. WTF?

So, I'll have to be brief this morning, and not supply much explanation. Before I do, I'd also say that you will get hugely different opinions on some of these issues, depending on who you ask. It gets a little like discussions of politics and religion. Based on my own self-study of expert opinions (I'm not a suspension expert) here's my 2¢ worth.

Anti-squat:
51% is too high for a light road car. A value between 10%-20% is better with 20% going to heavier vehicles like big
sedans.

Roll Axis Angle:
This calculator shows the rear roll axis angle in isolation. It is an important indicator of the rear suspension architecture, but of more value when you have the front roll center too. Then, the roll axis will be taken to be the imaginary line connecting the rear and front roll centers, either static or dynamic. That will be a better indicator of overall vehicle performance. Having the F/R roll axis angle and the roll axis of the rear alone the same (or very close) is considered ideal by some designers.

Roll Steer:
Neutral (as indicated in your output) is OK. Slight roll understeer is considered to be better for high performance driver control. Roll oversteer can be dangerous in a high powered vehicle - the rear end lets go easily in turns. Your V8 Locost is in that category.

Virtual Swing Arm Length:
In your graph, that's the length from the "instant center" point shown in your graph and the center of the rear axle shaft on your live axle. If it's too short, you can have bad behavior like wheel hop under acceleration or axle tramp under hard braking. It can also be too long. Without going back and re-reading some reference books, I can't remember what the "ideal" is for a live rear axle, but (I'm living dangerously here) yours may be at, or approaching, that now. You'll have to research that particular issue. If you don't have access to some good references, let me know and I'll try and make some time to find it myself.

Adding in Front Suspension:
All these values mean more (or less) when you have both a front and rear suspension design to look at. If you don't have a front design now, you might want to consider putting in the published dimensions for the Champion (Book) chassis front suspension. It will help you learn more about the front and rear as a system. That's what really matters most. If you have an "ideal" rear (or front) while the other end misbehaves, you'll not have a good design in the end, as one will spoil even the best attributes of the other.

If you're using a modified Book chassis, you'll have to alter the published Book suspension dimensions values to match the wider, higher or longer numbers for your chassis dimensions, as appropriate.

People spend years studying suspension behavior. It's complex, so don't feel you're an exception if it takes some time to get your head around it all. In the end, it's all compromise, and non-geometric factors like tires, springs and shocks do play a big roll too. If you don't get it "perfect" in the geometry, you can use those latter variables to tune your suspension once on the road.

I hope this helps, and hope that the darn thing stays posted this time. :BH:

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, 2017, 10:02 am 
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So on my front I will be aiming for a roll centre of about 2.5-3.5 inches. It is not yet designed though, I'm getting there.

I have made some slight alterations as per your input Lonnie, providing I have understood what you have said. I believe I have put more stability inducing understeer in the rear. I also feel that if I have multiple mounting holes (2 for top link on chassis side, 2-3 for bottom links on both sides I can alter things after it is built with our compromising strength and allowing me to continue forward instead of spending months making a perfect in theory suspension.

So you know my top link is a mustang one so distance can not be altered it is 8.46 inches long and that is that.


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Screen Shot 2017-04-14 at 7.51.53 AM.png
Screen Shot 2017-04-14 at 7.51.53 AM.png [ 123.43 KiB | Viewed 807 times ]

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Convincing yourself you can do it is one thing, convincing your wife it is a good idea is another. Glad I have a great wife!

2012 Jeep Grand Cherokee daily driver
Autocross car currently missing..... building a 1968 Plymouth Satellite with 7.2L of noise making technology.

Build is a plus 2" width, Ford 5.0. Wish me luck.
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PostPosted: April 14, 2017, 1:26 pm 
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Location: Carlsbad, California, USA
I hope that was some useful information, Ben.

This may also be helpful:

You can use the chassis mounting location of the Panhard rod to enhance/counter some forces under acceleration depending on if it's on the driver's side or passenger's side. Also the inclination of it (assuming it isn't parallel to the ground) can be used in the same way.

A rear roll center of ~4.5" is unusual for a live axle. The disadvantage is a low Panhard rod and the risk of snagging it on something. However, yours is located behind the wheels, so in many cases, the wheel rising up as you go over that "something" will protect it.

If you've had some algebra and elementary trigonometry, you can use the "slope of a line" formulas and the inverse functions of trig to calculate the angle of your full, front-to-rear roll axis using various heights of the front roll center. You already have some ideas about the front roll center heights you want (2.5-3.5 inches), and you've settled on a 98" wheelbase, so you'd be able to set up a simple sketch and figure the angle out for various front roll center heights.

If you can provide for some adjustability in your links as you've suggested, you can use that to tune the rear axle once on the road too.

Good luck with it.

Cheers,

Lonnie

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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, 2017, 12:09 am 
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Location: Langdon, AB Canada
Lonnie, I am sure this has come from many before me but a big thanks for your input. It is greatly appreciated.

I see what you mean on the panhard bar. The frame also can get in the way of trying to mount it that low... it becomes a puzzle. Like a puzzle I am very tempted to just start focusing on one bit at a time as my head is hurting right now and it just starts to feel overwhelming. :BH:

If I get the rear diff where I want it with the multiple mount holes, then fabricate the 3 link bits, and worry about the panhard bar after, how bad would this be? If all 3 links are parallel with one hole 1 inch above and below on all frame mount s could I not adjust with how it drives and handles afterwards? The way a vehicle handles is by drivers feel in the end anyways and every person has there own driving style, so I know there is no perfect answer, I just don't want it to be unsafe.

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Convincing yourself you can do it is one thing, convincing your wife it is a good idea is another. Glad I have a great wife!

2012 Jeep Grand Cherokee daily driver
Autocross car currently missing..... building a 1968 Plymouth Satellite with 7.2L of noise making technology.

Build is a plus 2" width, Ford 5.0. Wish me luck.


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PostPosted: April 15, 2017, 12:47 pm 
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Since you have the calculator, I'd say do a lot of "what if" scenarios to see how the angles of the links produce various changes. You'll need to use the "tester's mentality" and just change one variable at a time. For example, leave the two lower links parallel and only change the angle of the upper link, say in 1 degree increments until you get a result that you know is ridiculous and unworkable. You might get lucky and find that just making the upper link adjustable would give you a good range of behaviors to work with.

If just having the upper movable isn't sufficient, then look at making the lower links adjustable too, and then run through a series of scenarios where you: 1) keep the upper link parallel and alter the lowers by one degree each time; 2) secondarily move both the upper and lower by one degree each time and have them converging together.

There is so much that can be done with the Panhard rod too. For a road car generally, a long Panhard rod running level at ride height is considered the way to go. However, running it at an angle when viewed from the rear is acceptable too, but you need to understand what that means in terms of characteristics experienced at the wheels under acceleration, roll and braking.

There are a lot of Panhard rod products available in the circle track racing world, but they are mostly made for the Ford 8.8" rear axle. You have the 7.5", correct? So, you could just use the below for ideas and make your own for the smaller 7.5.

Here are some random products. For the Locost, there are often packaging issues to consider too. We don't have the space that the big, circle track cars have for gear like the below.

Chassis-side adjustable mount:
Attachment:
Adjustable-Chassis-Side-Bracket-Idea.jpg
Adjustable-Chassis-Side-Bracket-Idea.jpg [ 22.79 KiB | Viewed 741 times ]


Axle-side adjustable (rotate to move up/down) mount:
Attachment:
Axle-Clamp-3.jpg
Axle-Clamp-3.jpg [ 119.86 KiB | Viewed 741 times ]


Roll-your-own Clamps from Allstar Racing:
Attachment:
Allstar-Clamp-on-Rings.jpg
Allstar-Clamp-on-Rings.jpg [ 63.01 KiB | Viewed 741 times ]


I'm not trying to confuse you further, it's just helpful to know that there are a number of variables you can alter to get the rear suspension behavior you want. And, of course, there are springs, shocks, anti-roll bars and tires too. If you build some flexibility and adjustability into your design, it is highly likely you'll be able to "tune" your design to your liking once on the road, without making any structural changes to the car.

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 16, 2017, 2:47 pm 
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I actually do have a 8.8 so some of those options could be good for me. In others opinion though would a clamp on panhard bar mount really be sturdy enough? I just imagine a lot of force trying to make that clamp slide.... dose not sit all that well in my head.

I started making the other mounts as I feel I am close so with the adjustability I plan to integrate in the design I am sure I will be fine. Plus I need some forward progress to make me feel better, sometimes that just needs to happen.

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Convincing yourself you can do it is one thing, convincing your wife it is a good idea is another. Glad I have a great wife!

2012 Jeep Grand Cherokee daily driver
Autocross car currently missing..... building a 1968 Plymouth Satellite with 7.2L of noise making technology.

Build is a plus 2" width, Ford 5.0. Wish me luck.


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PostPosted: April 16, 2017, 7:17 pm 
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If you've got a plan - go for it. I know the feeling you speak of. Sometimes you just need to get things done with what you've got.

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: October 16, 2017, 3:17 pm 
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Location: Langdon, AB Canada
Everyone must think I am the slowest worker on the planet. But the point is I am still at it and won't give up. I put some of my rear suspension stuff aside (as I want to continue to practice my welding before I get to weld those parts) and decided to work on the floor, and frame welding (no longer just tacked). This way I feel progress and give my head a break and give myself some more welding practice. Once the base frame is done I see no reason I can not get the floor on, however before I do this, I thought lets use this great source to make sure I do not cause myself future headaches first.

I am welding on a 16gauge steel floor, I want a stiff chassis so want to make sure that no stiffening can be gained through the floor outside what the book chassis offers. Also would having a floor make it harder or make any difference in completing other things on the car. I still am doing engine mounts, suspension mounts, and some triangulation to add stiffness. Would a welded floor add enough stiffening to not worry about further triangulations within the passenger compartment floors, or transmission tunnel bottom.

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Convincing yourself you can do it is one thing, convincing your wife it is a good idea is another. Glad I have a great wife!

2012 Jeep Grand Cherokee daily driver
Autocross car currently missing..... building a 1968 Plymouth Satellite with 7.2L of noise making technology.

Build is a plus 2" width, Ford 5.0. Wish me luck.


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PostPosted: October 17, 2017, 1:51 pm 
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Location: Langdon, AB Canada
So my welding has really improved! Here is a small glimpse of 16 gauge welded to 16 gauge as well as to 1/8". I'm really starting to become happy with this.


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2017-10-17 11.49.27.jpg
2017-10-17 11.49.27.jpg [ 940.62 KiB | Viewed 244 times ]

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Convincing yourself you can do it is one thing, convincing your wife it is a good idea is another. Glad I have a great wife!

2012 Jeep Grand Cherokee daily driver
Autocross car currently missing..... building a 1968 Plymouth Satellite with 7.2L of noise making technology.

Build is a plus 2" width, Ford 5.0. Wish me luck.
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PostPosted: October 20, 2017, 2:47 pm 
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Posts: 97
Location: Langdon, AB Canada
Been welding the frame. Huge progress made. Also could not resist placing tires to get a vision of how this is going to look.


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IMG_20171020_123856_124.jpg
IMG_20171020_123856_124.jpg [ 1.42 MiB | Viewed 188 times ]

_________________
Convincing yourself you can do it is one thing, convincing your wife it is a good idea is another. Glad I have a great wife!

2012 Jeep Grand Cherokee daily driver
Autocross car currently missing..... building a 1968 Plymouth Satellite with 7.2L of noise making technology.

Build is a plus 2" width, Ford 5.0. Wish me luck.
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PostPosted: October 20, 2017, 3:20 pm 
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Nice! It's always good for the project to start to look like what it's supposed to be.
Now, put a piece of plywood across the floor in the driver's compartment, grab a steering wheel and go for a ride! :mrgreen:

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PostPosted: October 20, 2017, 3:43 pm 
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Those front tires are huge; what's the expected scrub radius, because steering effort may be an issue.

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Last edited by KB58 on October 20, 2017, 5:13 pm, edited 1 time in total.

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PostPosted: October 20, 2017, 4:09 pm 
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Gonzoracer: this has been done. The frame is even on casters right now so I can freely roll down my driveway. Lol

Kb58: answer right now.... I don't know, I have not designed the front suspension yet. I do plan to run 305 tires on all corners. It is the style I want more then all out speed. I will have an appropriate set of tires for autocross as well. Wheels and tires can always be changed so if it ends up unbearable it is easy to correct.

_________________
Convincing yourself you can do it is one thing, convincing your wife it is a good idea is another. Glad I have a great wife!

2012 Jeep Grand Cherokee daily driver
Autocross car currently missing..... building a 1968 Plymouth Satellite with 7.2L of noise making technology.

Build is a plus 2" width, Ford 5.0. Wish me luck.


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