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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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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")
Attachment:
85.jpg
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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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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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PostPosted: May 2, 2017, 3:57 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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Is there a model with a IHRA or close to IHRA legal cage?


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PostPosted: December 28, 2017, 11:23 am 
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I've been lurking around on the forums for a couple of years and am just starting to get serious about putting my upcoming project in CAD. I wanted to do a small chassis with an integral roll cage, but I'm about a 40" waist and 6'1" so I don't really fit in a book chassis-sized cockpit.

Here's what I came up with. Its based on a Haynes roadster chassis (CAD model from https://locostcadfiles.wikispaces.com/), and I substituted the upper and lower frame rails with 1.5" round tube, then built a SCCA-legal (I think) roll cage. I omitted the bend that straightens the frame rails through the cockpit, which adds about 6" at the base of the seats, but doesn't really make the whole car wider. The front hoop is designed to hold the windshield in the stock location. This will be for a street/autocross car, so my plan is to have a removable roof panel that bolts onto the top of the cage if I want to keep the sun off me.

I think you could make this into an IHRA legal cage by just adding the appropriate bars in the right places. (Edit - after reading the IHRA rulebook, I think this may be legal as-is if you use 1-5/8" tubing, but I'm not sure if they would classify this as a full-bodied car. I suggest talking to an IHRA tech inspector.)

It complicates construction in that you have to bend the bottom frame rail in 4 places, in plane, from a 20 ft piece of tubing. The rest of the cage is relatively simple. The other challenge is that you have to cut the scuttle in two pieces to sandwich around the tubes for the front hoop, but I think with some creative fabrication I'll be able to make that work.

My one big beef with this design is that there isn't a good structural tie from the rear downcomers forward to the main part of the cage, so the risk of the cage mouse-trapping down in a rollover is increased. I may add some kickers from front hoop and triangulate the roof bars to the front and rear hoops to help that. Also, for street use, with the rear stays at the very back, they're the first thing that gets hit in a rear-end collision so there's no crumple zone. I'm not entirely sure I like that.

I have .dwg and .dxf files for this, but they're too big to upload here.

Attachment:
File comment: Full frame
Haynes Roadster w cage.jpg
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File comment: Tunnel omitted for clarity
Haynes Roadster w cage1.jpg
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File comment: Original frame rails shown vs. cage rails to show added space.
Haynes Roadster w cage2.jpg
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Attachment:
File comment: With body and windshield in place. You can see where the frame exceeds the original bodywork.
Haynes Roadster w cage4.jpg
Haynes Roadster w cage4.jpg [ 45.08 KiB | Viewed 899 times ]


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PostPosted: December 28, 2017, 11:47 pm 
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You know, I never extrapolated out the line if you didn't make the bend in the frame. Only 6" huh? That's narrower than I expected it to be. That looks nice

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PostPosted: December 29, 2017, 1:03 pm 
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When I started on my Car9 design it seemed after going at it for awhile that there was little to be gained from retaining any of the original frame. It's just some details after you replace the main rails and graft in the cage. The details carry over some problems though and perhaps also some inconveniences. An example would be how the tubes go under the engine and then fail to meet up with the transmission tunnel tubes. When I did some stress analysis on the Locost frame that little piece of frame tubing by your ankles was the highest loaded tube in the frame and just using my normal test load it was around 70,000 psi. The highest loaded tubes on Car9 were under 15,000 psi if I remember right.

You need to make some simple models of parts like wheels/tires and uprights. I'm not good at drawing complex shapes so even just getting the location of the mounting holes is sufficient. I thought you would have a very high ground clearance, but now it occurs to me you may be planning on using fabricated uprights per the Haynes book. You do need to check that you can fit the wide frame between your wheels/tires. Maybe 6" will fit, but not sure. Have you chosen a diff and driveshafts yet?

How wide is the inside dimension of the cockpit at the driver? Car9 is 41.25" on the inside of the cockpit. I'm a similar size. Removing the tunnel structure saved some room for the passengers.

Having the rear roll bar supports attached to something strong was a primary design goal, it seems to be a real flaw with some of these cars. My third day out in a formula ford I put it backwards into a cement wall. :shock: Having a cage that is strong is a good thing. I have similar thoughts about the part of the frame box that the rear suspension attaches too. It just seems like an after thought sometimes. The Car9 rear suspension feeds into very strong parts of the frame.

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PostPosted: January 2, 2018, 6:33 pm 
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So I downloaded SketchUp and started playing with the Car9 model a little. It looks like the wheelbase on the Haynes chassis is 2" longer than Car9, which allows for the slightly wider frame. It actually encroaches into the vertical silhouette of the wheel, but because of the curvature they don't touch, assuming you don't have a ton of travel.

It looks like the added length is mostly in the cockpit area and behind the rear wheels, but I don't entirely understand yet how the packaging is different. I flanged up both models and you can see the result:

Attachment:
Car9 vs Haynes.jpg
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These models are mated up at the forward-most lower crossmember, rather than the front tires or something that would make sense mostly because manipulating this in cad is a bear.

I like the Haynes design better from an entry/egress standpoint, but the packaging on Car9 does work a lot better.

Edit: I apologize if I'm re-hashing stuff that's already in this thread. 30+ pages is a lot to read through.


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PostPosted: January 3, 2018, 3:17 am 
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Hi DaveH, what a great picture! Your welcome here if you're going to take the time todo things like that.

In your picture, Car9 should be moved a few inches to the rear. The front bulkhead should line up with the front tire centerline. On Car9 the front suspension wishbones have their forward leg perpendicular to the frame. Then one bulkhead is used to support the rack, coil-over mounts and the front wishbone legs. There would be lighter size tubing used to mount bodywork, radiator and fans etc. in front of that but it's sacrificial kind of stuff.

This picture shows up a couple of details about the Car9 frame that make it work so well. Maybe some of this would cross over to a Haynes, I'm not sure. If you move the Car9 back about 6"-8" the features might line up better. One thing you can see is that the scuttle area has a "W" set of brace tubes and that one well braced bay on the upper surface of the car makes a huge difference in it's stiffness. Then the nodes of that "W" brace are adjusted to meet the engine bay braces and also the optional "track bar" that goes over the passenger seat to the outer rail. The track bar completes the diagonal bracing from the front all the way to the rear of the car and improves the rigidity by an additional %50 for the cost of something like 3 or 4 lbs.

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PostPosted: January 4, 2018, 12:41 pm 
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I lined them up and added some comparisons. It looks like the big difference in packaging is in the scuttle location, with Car9 having it much further rearward, this allows the engine to be installed further rearward as well. The pedal box also moves back, and the driver seat is a little further back as well. I have both the stock and my modified models shown below.

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Car9 vs Haynes Iso.jpg
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Car9 vs Haynes Mod Iso.jpg
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Car9 vs Haynes Scuttle.jpg
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Car9 vs Haynes Scuttle Engine.jpg
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PostPosted: January 4, 2018, 4:19 pm 
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In those Car9 drawings the front braces for the roll bar would only be on a car where helmets were worn full time. I try to keep those things in different layers of the drawing. That probably means I should update the public drawings soon. So maybe that helps with the ingress/egress you were mentioning?

I did move the dash area rearwards a bit. It is closer to the proportions of an actual Seven in that way. Also perhaps some other older style roadsters.

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PostPosted: January 4, 2018, 5:29 pm 
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I have most of the layers on in this drawing. When converting from Sketchup to autocad, there are some elements somehow associated with multiple layers. I did this to see how all of the different modeled options look.

The whole point of this exercise is to figure out how to fit a full cage on one of these cars. I prefer a cage design like the one I had in my original model, with a high front hoop and connectors from the top of that to the main hoop. If I did that I wouldn't include the front braces shown here.

My comment on egress was mostly about the windshield-to-main hoop distance. With the scuttle being farther back on Car9, the "window" you're having to climb out of gets smaller. Combined with a tight interior and the upper cage members, it can make getting in and out significantly more difficult. If I go down the Car9 route, I'm likely going to just plop that front hoop down onto the frame where I want it.


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