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Learning how to build Lotus Seven replicas...together!
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PostPosted: April 4, 2017, 11:54 am 
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Joined: May 28, 2006, 10:52 am
Posts: 21
horizenjob wrote:
Getting in and out of the car becomes an issue though and people take different approaches to this. I think I like something that involves a step on the side of the car, followed by stepping over the rear roll bar and into the car. Then you can stencil "Step" and "No Step" on the car just like any good fighter plane. :)

The in/out issue comes from how you decide to connect the front and rear hoop at the top.

The front hoop probably requires moving the dash bulkhead forward just a bit and then the dash would hang from a few inches up the hoop. Let's do some pictures. Alfameister are you familiar with SketchUp or willing to learn a bit?


1. My SketchUp knowledge is nil (except for being able to open your file), and just recently, discovered the "layers" function.

2. Going in and out is not a problem - I just kinda mosey down my body there somewhere (Actually, I get in like I do on a kart - step on seat or floor, hold/grab roll cage to support myself, and mosey down the body). As it is only a track car and weekend car (can't/won't daily drive it as AIR CONDITIONING is practically a must here in the Philippines), the getting in and out is not a concern.

Here is my Locost ("7" logo shipped from the USA from botbasher all the way to the Philippines, LOL - had to have that "farkle")
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Anyhoo... been reading (all 33 pages... that took a while), and I see that the SketchUp files are more like a guideline than an actual "cut list" or cookbook approach - I have read that you can make it longer or wider as it pleases the builder. When I start (maybe in August 2017), I'll probably keep it close to "book" dimensions -- besides, smaller car, lighter weight.

Not yet sure how the taller frame will affect my driving (elbows hitting or whatever), but so far, in my book chassis (with Cymtriks mods), driving it is fine. Also haven't studied yet if taller frame is a condition for Car9 (or if I can stick to about book height).

I'm going to have to work on suspension geometry for my Car9. I don't have access to the ubiquitous (in the USA) Ford stuff; Miata stuff are a bit pricey. We do have lots of Toyota (mostly Corolla/Altis) parts. Also Nissan, Mitsubishi, Honda (the smaller cars like Civics; Accords are rarer/pricier) - basically, small cars are more common (because they're more affordable for Filipinos).

(My Locost has a Toyota 4AGE engine, about 160-ish hp, and, so far, enough. Even with mods or a complete engine change, a tad over 200 hp should keep me happy; no need for all that 300 or 400 hp for me). What I'm trying to say is that, Car9 can be built for monster V8 engines, but I'd like to keep the build light for my lower powered powerplant choices. How heavy is Car9 again vis-a-vis Champion's book frame (but, let's make it apples to apples -- the book frame doesn't have a roll cage, for instance).

Am sure I'll have more questions. Basically, though, it's not like a totally scratch built car -- I'm just thinking of "upgrading" my car by changing out mostly the chassis - kindly like a chassis frame transplant. Of course, I'll have to change the live axle (which I don't mind doing anyway).


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PostPosted: April 4, 2017, 1:58 pm 
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The voice of reason
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What a beautiful Locost you made! I really like your attention to detail on things like the driver side protection bar. It joins to the roll bar diagonal and then it gets painted white along the side and connects into the frame.

There is a lot of use of the layer function in SketchUp. Working on it last night and trying to include round/square tube, short/tall roll hoops, track/street cage variations - I think I am past what can be done this way. So I may need to break up the models and separate them. The layers work great for things like different size wheels and some other things, but at some point stuff starts to conflict.

It's hard to compare the weight of the frames. Early Sevens did not have a driveshaft tunnel and would not have stood up to the loads of modern engines and tires etc. at least not with the longevity people expect. Do you have a guess as to how much weight the Cymtriks mods weigh? A big factor is how much of the frame lands up being roll cage spec material.

If you choose to use 1.25" x .065" tube for the main frame, that is the same weight as 1" square but stiffer. Then you get a little extra weight because I spec 1"x2" tube for suspension mounts and I use main frame tube size in hoops around the rear fuel cell. Those changes are around 10-15 pounds. In my car the large tubing is 1 3/8" x .065". The upper rail, tubing around cockpit and cage are 1 3/8" x .083" to meet racing specs.

Potentially you can cut the roll cage off your Locost and use it on your Car9.

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PostPosted: April 4, 2017, 7:41 pm 
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One of the attractions for me about Car9 is that it is a roll cage first, then the chassis attached to it to hold the engine and suspension. The Locost frame is the opposite - frame first, with the roll cage as an afterthought.

I never weighed my frame, nor the car (I plan to corner-weight it one of these days with the locost method of bathroom scales and wooden planks for leverage, something I read in the all-knowing internetz).

I know my Locost is heavier than book chassis - original frame builder (I just bought it off someone) used heavier gauge steel than what was required, and sometimes even bigger steel (he didn't use any 3/4" RHS). He said he wanted it overbuilt - he wasn't a track oriented guy, so has not even heard of the "add lightness" philosophy.

If I had to do it over, which I was planning, I would have stuck to following the book chassis as per spec (frame builder made several changes, and some of it I had to redo; had to cut down and remove tubes, and re-weld), and still add the cymtriks mods. And then add a roll cage (when my friend said that the Seven was a potential widow-maker, the cage became a must).

Then I came across Car9, and rather than re-do my book chassis, maybe use the Car9 frame (plus, I get to do IRS instead of a live axle).

I also came across a guy who did a 15,000 ft/lb chassis:

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Taken from this 45 min video (designing a race car using open source tools; I just used youtube's 1.5X speed to watch it in 30 min):

https://www.youtube.com/watch?v=VigVEbeTtXM&t=88s

This is the car he (Dave Chinner) crashed, which is a book chassis, which prompted him to make a new chassis:

https://www.youtube.com/watch?v=3ow1mJZ81xI

Quote:
In analysing the corpse of my car - mostly based on the book chassis - I realised that I needed to make something far stronger. Not just for safety reasons, but also to handle the suspension loads generated by modern race tyres and ludicrous power and torque of my race spec engine.


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PostPosted: April 5, 2017, 12:08 pm 
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I would have replied last night, but watched the video which is pretty long. I was hoping to see Open Source tools measure up but it seems they are a long way still.

The first big takeaway from his video is the issue I caution our builders on with high power cars. He shifted into 3rd I think at about 95 MPH and lost traction at the rear and hit a wall. If you spin the rear wheels at high speed you may not hear it or feel it soon enough to prevent big problems.

There are a couple of FEA programs we use to analyze the frame, Grape and Lisa. We have models for a Locost frame with mods and Car9 for Grape. I put hundreds of hours of effort into Car9 with the FEA model. These models will also tell you the weight of the frame. I think in the case of the fellow with the video above issues with his tools took up much of his time that could have been spent on designing the frame. I'm sure it was frustrating for him.

The second takeaway is do not early apex like he does! You do not want to run out of road at high speed on the corner exit.

Alfameister you seem to have reasonable priorities. You should be able to meet the weight of your current car pretty easily. There are some basic choices you need to make up front. The big two I can think of are square tube verses round and a rear roll hoop that reaches the floor or the top rail. When the hoop just reaches the rail the tubing beneath it is also roll cage spec so I don't think the strength is an issue - I did this because it's easier to get a tube 8 feet long shipped to my house.

You can use the SketchUp diagrams to produce a cut list, but what happens when you bend your rollbar and it's 1/4" narrower than you wanted? I will let you guess wether my entire car is 1/4" narrower than I intended. :rofl: If you are sourcing metric tube, you would have to change some dimensions anyway, once you change them a bit you might as well make them what you want.

Do you have access to a good tube notcher and bender?

I don't object to fitting a live rear axle if you want, but not sure I recommend it - no one has worked out how to fit a Panhard bar or somesuch for Car9. The big advantage is the IRS will be a more comfortable ride and here in USA our live axles mostly come from trucks and are very heavy.

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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.


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PostPosted: May 2, 2017, 3:57 am 
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Joined: May 28, 2006, 10:52 am
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What's new in Car9T?

(btw, sent you pm Marcus)

Just happened to check in here and the Car9 website, and there's a new upload.


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PostPosted: September 27, 2017, 3:51 pm 
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Joined: December 20, 2016, 11:38 pm
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Is there a model with a IHRA or close to IHRA legal cage?


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