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Learning how to build Lotus Seven replicas...together!
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PostPosted: June 3, 2016, 8:36 am 
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Marcus, is there any added benefit to adding an x or diagonal brace to the chassis right behind the radiator? Does the radiator act as a brace?

Can you make the w brace around the engine removable to make access to the engine easier? Similar to a strut tower brace?

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PostPosted: June 3, 2016, 11:18 am 
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It's hard to see in the picture, but there is a V shaped brace in the front bulkhead. You can click on the picture to see a larger version. This version of the model is the working version for my own car. I've been trying to keep accurate models for each of the cars being built, so there are differences. This one, just like my car on the table, is not tidied up yet.

I guess you could make the engine bay diagonals removable, but there seems to be a lot of room. That may change when I actually have to work on the engine though. :) Tom has been able to put in and remove his engine with transmission attached a couple of times now and his engine is a couple of inches larger than my Ford Windsor.

I would be a little concerned about making them removable though...

Also to better answer your question, there are significant loads on those diagonals at the front bulkhead. We also try to provide significant stiffness in the dashboard hoop area of the frame by using a vertically oriented 1"x2" in the floor there and providing inner tubes to create an inner hoop on the sides of the cockpit.

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Car9 Roadster information - models, drawings, resources etc.


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PostPosted: June 3, 2016, 12:39 pm 
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Marcus, I like your engine bay framing. That will be on my list of things to try. I also like (how do I say this) your rear end. Your triangulation here looks good for lateral torsional stiffness.

To keep a perspective, I attach a chart of torsional stiffness requirements. I’m told that torsional stiffness is one of those things you only need if you don’t have it. I’m also told you can reduce the 10% value for a good car but should increase it for a bad car? Who knows?







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PostPosted: June 3, 2016, 12:40 pm 
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Whoops, here's the chart


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PostPosted: June 4, 2016, 3:54 pm 
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Here’s generic Locost with full metal jacket. I applied some very basic triangulation and went from 400 ft lb torsional rigidity and 95 lbs of steel untriangulated to 2100 ft lb per degree and 160 lbs of steel triangulated. I can now start to play with individual pieces. Let the fun begin.


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PostPosted: June 21, 2016, 2:21 pm 
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For an update, here’s generic Locost with the larger tube (1 ¼” x 1 ¼” x 0.063”). The engine bay is the soft point and I will play with that next.


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PostPosted: June 23, 2016, 1:21 pm 
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I think you may have clearance trouble with that diagonal under the engine oil pan.

Andrew Moore and I found you had to make some basic changes to make a lot of progress. You can't just throw more metal into the standard Locost frame. I don't remember Andrew's numbers exactly but they are in this thread much earlier on. Car9 came in around 8-12 thousand ft-lbs/degree at around 175 lbs. or tubing. It took a lot of work to get there.

In addition to what you're doing it helps to do some stepping back and try to figure out some fundamental changes. It's hard keeping all the stuff in your head while your doing this. :shock: You make some changes that work, then you backtrack and change something else and then what you did later no longer works.

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Car9 Roadster information - models, drawings, resources etc.


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PostPosted: June 23, 2016, 3:18 pm 
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Is it possible to replace some of those triangulation tubes with sheet metal? I have a standard frame, but with a steel floor, firewalls, and transmission tunnel sides the car is incredibly solid. You need those panels anyway.


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PostPosted: June 24, 2016, 11:54 am 
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I can see figuring one of these is like those puzzles where you try to get all the little balls in the holes at once.

Horizonjob, my congrats on your numbers. I know what it took to get there. I think your engine bay bracing is key. How many different tube sizes did you wind up using in your locost?

Nick47, as suggested, I’m thinking of trying to replace a tube with a sheet to see what happens. The analysis program allows for that. This program is also used to design girder bridges which are essentially just trusses with the diagonal pieces replaced by the web plates. Plate FEM can be tricky but I have to try it!

Attached is my first shot at stiffening up the engine bay. Just a piece of large diameter tube tied onto the frame. This could also double as a fresh air intake, or you could make it look like a 6-71 blower. Or hide a blower in there if not permitted by rules? This is absurd but it shows you can add stiffness externally if you have room for it.


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PostPosted: June 24, 2016, 5:54 pm 
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Here’s the generic Locost with the diagonal tube in the lower engine bay replaced with a 0.063” thick steel sheet. The torsional rigidity doesn’t change much. Which means tubes could be replaced with sheet, except for the attachment difficulties. I didn’t compare weights.

Note the fore-aft distortion in the rear of the frame. I haven’t explored any rear framing yet and this looks like another soft spot to play with.


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PostPosted: June 28, 2016, 1:02 pm 
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I did some more study on car9 and I see where you are picking up rigidity at the cowl and the tail. Well done! I also note a lack of framing around the driveshaft tunnel. I think there was another discussion somewhere about how this steel is better off distributed out where it has leverage against torsion. I agree.


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PostPosted: June 28, 2016, 2:02 pm 
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ps to post above: a reinforced driveshaft tunnel can provide rigidity to an otherwise soft driver/passenger bay like that tube did to the soft engine bay in my earlier post. But farther from center is better up to a point.


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PostPosted: June 29, 2016, 11:05 am 
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I'm continuing my study of Car9.

Marcus, is this your proprietery design? I wasn't able to download the technical data on the site you posted.


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PostPosted: June 29, 2016, 1:07 pm 
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Hi Bob, no I don't intend for the information to be private or anything. I'm in and out with some chores during the afternoon, but I'll look into why stuff doesn't seem available, that's not good. Thanks for trying and letting me know.

What should be available is the SketchUp drawings of the car and it's parts and the FEA model in Grape. The FEA model files are simple text, so easy to read. One of the files contains the dimensions of the tubes and the X,Y,Z coordinates of where they join. It's easy to tell the dimensions from that file.

It was nice to see the result you got from the steel plate under the engine. It might not work to put one there in real life, but now you know you can put sheet wherever you want and see what the effect is.

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SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.


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PostPosted: June 30, 2016, 10:22 am 
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Bobber, after a day I have remembered there is a table of contents for this thread in the first post. I have moved that table of contents to the top of the post, which seems a sensible place for it. There is a link there to a Grape FEA model for Car9.

I was able to download the FEA and SketchUp models from the "Car9 Roadster information" link in my signature. Is that what you had trouble downloading? I did fix the signature link to the SketchUp 3d model warehouse, which also has models.

I'm happy to provide and update these models online, if you let me know what you want. Thanks for asking.

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SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.


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