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Learning how to build Lotus Seven replicas...together!
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PostPosted: November 22, 2017, 10:48 am 
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Hello all,

New member here, so please excuse if I have this in the wrong place, and Mods please move as necessary.

Anyway, Good morning all.

A long time ago I bought Ron's book and some metal. Then I got pulled into Experimental aircraft and set the car aside. Now many years later, I am back to the car and have found a huge amount of development here by some way creative people.

Now, moving ahead, I would like to build a track car for the NASA ST3 class initially. As this is a power to weight class, 1000CC bike engine, light weight and stiff for the track seem to be just what I will enjoy. Road going is not important to me, so planning low ride height, no creature comforts, road race legal. I have been using 4130 steel on the aircraft and really like how it works with the TIG unit so I am planning on that for the tubing. I know a completed car will be cheaper/faster/etc... but I really enjoy the fabrication so into another crazy project I go. :D

My question is does anyone have suggestions for the chassis and suspension designs. I have several of the regular books on race car chassis and suspension design and can muddle through it if necessary, but why re-invent the wheel if others have already established some development and a base to start from.

I have driven an original wing fender lotus and fit just fine, so I don't need a +2,4,8 and don't want a V8 so longer and wider is not important.

Thanks for your help. I have begun to dig around the board, but I'm sure there are relevant threads and builds I am missing.

Brian


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PostPosted: November 22, 2017, 12:40 pm 
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Welcome, Brian.
Sounds like a good plan. There is a lot of good info to be found among this group. Here are some links:
viewtopic.php?f=10&t=9392
viewtopic.php?f=35&t=2027
http://underwood-racing.com/project_seven.htm
My number one advice, that I keep repeating, is don't get too hung up on particular frame dimensions. The book and other plans are great for the basic frame design/structure. However, I think it is far more beneficial to lay out all your components on your build table, and then adjust your dimensions accordingly. For example, you may want to off-set your tunnel or you may want to move some tubes to accommodate a roll cage.
Looking forward to your build.

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PostPosted: November 23, 2017, 2:10 am 
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mgkluft wrote:
don't get too hung up on particular frame dimensions. The book and other plans are great for the basic frame design/structure. However, I think it is far more beneficial to lay out all your components on your build table, and then adjust your dimensions accordingly


Oh how true this is! Saves the frustration of cutting apart a fully tacked frame to build it the way it should have been built the first time. On the other hand, it's good for practicing welding and rewelding :cheers:

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PostPosted: November 23, 2017, 3:01 pm 
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mgkluft wrote:
My number one advice, that I keep repeating, is don't get too hung up on particular frame dimensions.


If you're going to purchase a nose cone, buy that first and build the front of the frame to fit.

Also, scope out your rear suspension bits. Sometimes you can come up with diff + axle length + wheel offset that will work if you adjust the chassis width a bit one way or the other, and save having to go the custom axle or shortened housing route.


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PostPosted: November 23, 2017, 3:43 pm 
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If you are entering into a power to weight class I would think making the car as light as possible would give the greatest advantage. Personally I would make more of a formula car style with a single centered seating position and the motorbike engine in the back.

Get a seat put it on the floor and sit in it, get comfortable in the drivers position and mark where the pedals need to go. Hold a steering wheel to figure out where that needs to go. Then build the frame to accommodate you and all the other components. I would try to get it as small as possible with the components you have/plan to use.

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PostPosted: November 23, 2017, 5:17 pm 
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Component layout first is a great suggestion the look is approximate to a seven but there are no exact measurements I have to meet so there is a lot of room to adjust an inch here or there. Also thanks for pointing out those threads/builds, I had seen the orange one but that was it.

And axle/diff layout is an awesome suggestion as well, hadn't even thought of that. Especially as this dimension isn't critical and there is definite monitary impact there.

Single seat like a formula 500 with a rear engine isn't going to work. Part of selling it to the wife is the classic look and the second seat (even if it will never get used... But the goal is lightest weight that is reasonable. Sizing the tubing in 4130 steel will have to be something I delve a little deeper into as there is a couple pounds there but need to ensure the appropriate amount of stiffness as well to build a solid platform for the suspension to work from...

Thanks for the help, much appreciated.


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PostPosted: November 24, 2017, 2:22 am 
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Sounds like fun. Start reading that rulebook, carefully. Have a talk with someone about in the organization about wether they see issues with a Locost competing. Tube frame cars can have issues with the rules. I haven't read the NASA rules recently.Can you give us some more info like what you are expecting for a power to weight? If you go light, you might drop off the bottom or top of their scales... Is there a minimum weight?

I like to put a word in for my design, Car9. We have SketchUp drawings for it and also the FEA mechanical analysis available. It doesn't really matter what size you build it, it's the arrangement of the tubes that provides it's strength and stiffness, not the wheelbase or track width to a certain inch measurement. I designed that frame as something like a legal road race roll cage with the rest of something that looks like a Seven grafted onto it. I felt more comfortable with that idea compared to a light weight frame with a heavy roll cage welded to little tubes that weren't braced for loads at those spots.

I don't have strong opinions on the type of tubing to use, the crucial part is the roll cage and that material may be called out in the rules. I don't think the 4130 will give you a weight advantage. Unless maybe they spec lighter tubes for 4130 roll cage material. Airplanes do great with light 4130 tubing but their design does not really include impacts on cement walls or other cars. Mild steel tubing that is 1" x .063" will not be very highly stressed if the frame is well designed. Much of the frame will be roll cage and it will be much heavier tube. 4130 is nice material though and you may feel you can get better quality material in that alloy.

One neat feature in Car9 is the frame is designed with an optional ( it's removable ) stiffening tube that crosses the passenger side seat. It runs from the center of the dash to the outside rail at the roll bar. This one tube at about 3 lbs. adds an amount of stiffness to this car that's about equivalent to the entire stiffness of a Locost chassis that's been modified to be stiffer. That's because the frame is designed for that tube to complete the triangulation all the way from the front to the rear of the car.

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PostPosted: November 24, 2017, 10:40 am 
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The locost should work as a lotus 7/catterham/etc... type within the rules as long as I call it a 7. There is precedent for this with others...SCCA on the other hand has no place for something like this, which makes event choice simple.

The classing is based on power to weight with modifiers for forced induction, tire size, aero mods, etc. There is a light weight penalty, but the lotus/catterham is exempted from it. Power is calculated by 3 dyno runs and weight is minimum racing weight with the driver on board.

the classing is as such:
ST3 - 9.00 #/hp and up
ST2 - 8.00 - 8.99 #/hp
ST1 - 5.50 - 7.99 #/hp

I will have to look closer at Car9. from a quick look I assumed it was for the V8 crowd with the larger sizing and the mock-ups.

On the Car9, how much heavier is the base chassis from a standard stiffened one?

4130 does do a bit better in calculations, but as you implied, the quality has been much better (and more consistent) in my experience and it welds soooo nice :D

Of course, bouncing the design off the rules is required and not just once but all the way through to the track and beyond. How totally competitive it would be is a guess but will be fun one way or another. Aero is always going to be a limitation and I'm sure a tighter and more technical course would suit this type better in class than the big open tracks but corner exit speed takes a good bit of pavement to make up even down on total power due to the light weight to stay in ST3.


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PostPosted: November 24, 2017, 3:46 pm 
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Car9 was originally conceived for I4 engines, but my first builder, SeattleTom, had a love for pushrod Chevy engines that proved incurable. So in order to help ensure his success I also bought a pushrod V8 but went for the somewhat more modestly sized Ford small block ( originally a 221 CID ).

There is a Ford Duratec in the drawings and also at least a simple drawing of a motorcycle engine provided by Joshua Briggs. The I4 engines are pretty tall and I think that includes many bike engines because of the intake arrangement. The bike engine may be a good choice for track because you get a close ratio transmission with high gears. You won't spend much time under 60. Still this is an area to keep an eye on.

You can run a stock Ford Duratec at 170+ HP without problem and still have to build a pretty heavy car (1530 lbs). Plan on a fairly heavy duty stainless steel floor, which is not really a very bad thing. With a 170 HP you could be in ST1 and still carrying ballast if you really try. This opens up your choices on bike engines, get as much displacement as you can with a motor tilted towards cruising and a wide torque/HP band.

I am glad you're understanding already the issues of aero and track size etc.

Car9 is not especially wide but certainly wider than a real Seven. One thing is it was drawn to use a standard steering rack without having to shorten it. If you don't mind shortening a rack or buying a short rack ( they cost a couple hundred dollars extra ) you can make it quite narrow. It already has a pretty short wheelbase but you can make that shorter too. If you make it narrow, I thought a good idea was cycle fenders on the rear wheels in addition to front, but that might be hard with really wide tires...

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PostPosted: November 25, 2017, 3:45 pm 
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DO you have a strong opinion about IRS vs. a solid rear axle? THe IRS will be a good amount more comfortable on the street and it's a little hard to get appropriate light solid rear axles, money can cure many things though, if you want a Winters mini sprint aluminum quick change axle.

Another thing is Car9 doesn't use a driveshaft tunnel made of tubing so that could help you get the car narrower without getting too cramped, save you an inch or two.

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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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