LocostUSA.com

I just spent 2 weeks doin' absolutely nuthin' and loving it, but we're headed home tomorrow. I'm so relaxed, I don't know how I'm going to motivate myself to do any hard work next week. Oh well, I've got Saturday to poke around in the garage and pretend like I'm doing something and then I'm saved by an early Chargers game on Sunday, so that will give me some time to figure out a program.

Thanks for asking.

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

Welcome back! (Where did you go?)

I’ve started suspension design for the Das Boot and attached some sketches. I used VSusp until I went blind and figured I would just design the suspension to be adjustable for all likely roll center heights, instant center locations, and camber gain ratios. If I can do this, it will be road tunable and I can do a “real life” VSusp experience.

I also explored rising rate bell cranks for the coilovers.

I planned on some fancy sliders to mount the inner pivots but so far I haven’t come up with anything worthwhile. I’ll probably just settle on removable pre-drilled side plates for the inner Heims.

I ghosted in the front profile of a McSorley for reference. I was hoping to come up with a suspension concept that could be adaptable to a tube chassis also. Suspension design continues.

Bo
(there’s too many Bobs here so……)

We were on vacation in the mountains - it was very nice.

You know, if you're actually committed to building a Locost from your own design, there would be nothing wrong with starting a build log of your own and doing these design iterations there. It's OK to start down a design path then change course based on the realities you encounter along the way. I think our problems and dead-ends and how we overcome them are often more helpful and inspiring to others here than our simple successes.

In my case, I did buy a donor vehicle and had it when I started my build log. However, about my third or fourth posting was a screenshot of the beginning structures of my custom version of the Haynes chassis. It took a while to complete that design before building the actual car. It's something to consider, anyway.

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

I've started control arm design and made the attached study of threaded adjusters from Midwest Control along with some jam nut dimensions to see how everything can fit together. When you get the jam nuts in place, there is not a lot of room for adjustment and still have good thread engagement.

Bo

When you are using those bung adjuster nuts with the counter threads, I think you need an basic length adjustment at the other end and then you use this to adjust for a half or single turn. I considered using those to fine adjust the toe on my rear wheels because a half turn of a rod end would be too coarse for that.

BTW this is just not an appropriate thread to put everything into. How about getting a build log going. It can go in the "In theory" section until you start welding metal. Or somewhere else...

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

Hi everybody,

I am looking for the 3D drawing file of the 442e frame with the following extension, would somebody happen to have it already done?

Cad file
.dxf
.vap (this one would be the best)
.sdt/sdnf

Thanks a lot

Yohan

Yohan,

Jim McSorley provides some data on his website:

At this location you will find the 2D files ==> http://sevenesque.com/plans/

Only the 442 is provided in 3D ==> http://sevenesque.com/3d-models/

You can find a STEP or IGES version done by someone else here ==> http://grabcad.com/library/mcsorley-442e-chassis-1

I have no information on the last provider, but you can compare the 3D model to the dimensions on the 2D drawings Jim provides using the measurement tool in your 3D package. Both the STEP and IGES formats are well-known 3D interchange formats and just about every 3D modeling system supports them.

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

Hi Lonnie, thanks a lot for your answer. I got to talk with Marcus and some friends about it and it looks that if I can find a .DXF file of the frame we could easily transfer it. Do you know if Grape or some other software could transfer the 442e STEP file or the book drawing done by A Moore from the Grape file to a .DXF??

Thanks!

Yohan

Yohan,

There are a number of conversion utilities available. Some are online and free and some are $$$-only. Do a Google search for "STEP to DXF converter" and you'll see several of both types.

CAUTION: I've not used any of them, so can't say if they're accurate. The good news is that the 442e file is pretty simple. Also, sometimes "free" downloads are the carriers of viruses of various types. Make sure you have a anti-virus package installed and running on your computer. Converting online might be safer. Here's one example:

FREE converter (online or download) ==> http://www.anycad.net/the-free-3d-model ... nge3d.html

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

Hi,

Just to let people know I found that Grape can save the files in DXF. You just have to do ''save as'' and it is done. It can then be exported in many different software. We tried it and the only thing is the nodes and element comming from Grape cannot be changed but it is possible to add new things.

Have a great day!

HOW MUCH TORSIONAL RIGIDITY IS REQUIRED IN A CHASSIS?

ps.: sorry about the caps - that's the way we were taught

SOME SAY CHASSIS FLEXIBILITY FROM TORSION SHOULD NOT EXCEED 10% OF THE SPRING RATE AT THE WHEEL, OR, 90% OR MORE OF THE WHEEL RATE SHOULD COME FROM THE SPRING AND NOT FROM CHASSIS FLEX.

SOME SAMPLE CALCULATIONS:

ASSUME TORSIONAL RIGIDITY = 5000 FT LB PER DEGREE

ASSUME TRACK = 60 IN, OR 5 FT

FORCE AT TIRE FROM TORSIONAL RIGIDITY = 5000 FT LB / 2 TIRES (HALF GOES TO EACH TIRE) = 2500 FT LB TORSION TO EACH TIRE

EQUIVALENT LOAD AT EACH TIRE = 2500 FT LB / 2.5 FT = 1250 LB

LIFT AT TIRE FROM ONE DEGREE CHASSIS ROTATION = 30 INCHES x TANGENT OF 1 DEGREE = 30" x 0.0175 = 0.52"

EQUIVALENT WHEEL SPRING RATE FOR THIS LOAD AND ROTATION = 1250 LB / 0.52" = 2404 LB PER INCH

IF YOUR WHEEL SPRING RATE SHOULD BE LESS THAN 10% OF THIS, YOUR SPRING RATE AT THE WHEEL SHOULD NOT EXCEED 240 LB PER INCH OR ELSE CHASSIS FLEX IS DOING THE SPRING'S WORK

It isn't about chassis flex doing the spring's work (that's okay) - its about the chassis flexing and not allowing you to distribute the roll stiffness to balance the car.

The whole car is just a a bunch of springs in series. If something is too soft it is going to dominate the stiffness number and what you do to the other springs will have little effect on the overall stiffness.

If you have a soft chassis your anti-roll bars won't work effectively and you won't be able to change the car's balance. The 10% rule makes the chassis sufficiently stiffer than everything else that its spring rate doesn't matter.

1/(K equivalent) = 1/K1 + 1/K2 + 1/K3 + ...... 1/Kn

K equivalent is the total spring rate. You can see if K1 is very small (IE a very soft chassis) it will dominate the total stiffness number.

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-Andrew
Build Log
Youtube

So, looking at a chassis torsional rigidity of 2400 lb per inch effective wheel rate with a sprung wheel rate of 240 lb per inch yields an effective wheel spring rate of 218 lb per inch. The chassis torsion portion is undamped.

This gives a good idea of what chassis torsional rigidity does and doesn't do.

I remember computers before they had lower case... Shouldn't admit to it though.

Bobber thanks for posting this, looking at the stiffness as an equivalent spring rate makes sense. I'm not sure we are getting the right number though, it seems too low from just my hunch. My recollection is my FEA model shows less than 1/2" flex from a 2000 lb. load on one corner. Maybe the divide by two is wrong in your math? Or maybe working out in the cold has slowed my brain down...

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

Marcus,

My example was just a hypothetical one to help me understand the numbers. I think Lonnie and I discussed the division by two thing - for torsional rigidity calculations, I apply a torque force upward on one wheel and downward on the other. Hence the torsion split into two. Doing this counteracts some of the frame droop (bending) from a single force to give you a more pure torsion effect. But for real world loads, you take the total load on just one wheel while restraining the other three because that's more the way the real world is.

Does this make any sense? I'm still figuring it out.